Packing Papers.

This term may be applied to wrappings specially treated with substances which render the paper air and water proof. They are principally used for preserving food, or such articles as tobacco, which require to be kept slightly moist.

Waxed Paper.—The paper in the form of a continuous sheet is passed through a bath of melted wax at a high temperature, any excess being removed by squeezing rolls through which the hot waxed paper is passed. The paper is led over skeleton drums and thoroughly cooled before being cut into sheets.

Butter Paper.—Ordinary parchment paper is generally used, but for special purposes a solution containing albumen and saltpetre is utilised for impregnating paper.

Hardware Paper.—Needles and silver goods are frequently wrapped in paper impregnated or mixed with substances which are supposed to prevent deleterious fumes from coming into contact with them. The use of black papers heavily loaded with pigment, sized with glue and an excess of alum, is commonly resorted to. For silver ware, paper dipped in a solution of caustic soda containing zinc oxide is used. A recent patent suggests the impregnation of paper with heavy hydrocarbon oils, which being slightly volatile cover the goods, such as needles, with a thin film.

Paraffin Paper.—Large quantities of this paper are consumed for packing food and other articles which need protection from air and moisture.

The paper is either passed through a bath of paraffin or passed over a roller which rotates in a trough of paraffin.

If the paper is to be coated on both sides it is passed through the bath containing the paraffin in a melted condition, the excess of which is scraped from the paper as it leaves the bath. The paper is cooled by exposure to air, and when the paraffin has solidified upon the sheet the paper is wound up on a roller at the end of the machine.

If the paper is to be coated on one side only it is passed over a heated roller which revolves in a bath of melted paraffin, the other operations of drying and finishing being the same as in the case of a paper coated on both sides.

Tinfoil Papers, required for packing tea, coffee, and similar foodstuffs, are prepared by coating cheap paper with a solution of gum and finely powdered tin. The manufacture of the fine powder is accomplished by melting tin at a low temperature and shaking it continually as it cools down, whereby a mixture of fine powder and large particles is produced, the latter being separated out by agitation of water.

Tin in a fine state of division can also be obtained by a chemical process. Granulated tin is dissolved in strong hydrochloric acid, the solution diluted with water, and a stick of zinc introduced into the solution. The tin is gradually precipitated.

The dried powder is coated on to the paper with gum, and when the paper is dry the necessary degree of brilliancy produced by suitable calendering.

Transfer Papers.—A number of important operations require the use of what are known as transfer papers, so that a design written or printed upon a specially prepared surface can be transferred to another surface from which duplicate copies may be obtained. The principle upon which all such operations are based is the coating of suitable paper with starch, flour, and gum, singly or mixed, so as to give a surface firm enough to take the design, but which readily breaks up when the printed side is pressed against the wood, stone, or metal object intended to receive the design.

Thus a paper may first be dusted over with dry starch, or coated with starch paste and then dried. A layer of dextrine may then be put over the starch coating, and the design printed upon the dextrine surface. When the paper is turned face downward on a sticky metal plate the design adheres to the metal, and the paper is easily pulled off, owing to the dry starch layer between it and the dextrine being non-adhesive.

This principle is utilised in producing designs upon tins used for packing, metal advertisement plates, domestic articles of every kind, stoneware and earthenware goods.

It is further applied in the preparation of lithographic stones required for printing.

Each class of work demands paper of a suitable character, but the principle of an easily detached surface-coating is the same for all. The main difficulty experienced is the liability of paper to stretch when damped, and various methods are devised to obviate this, either by employing paper which stretches very little when damp, or by making the paper partially waterproof before use.

Papier-mâché.—This name indicates a preparation of paper or paper pulp mixed with various mineral substances firmly cemented together by animal or vegetable adhesives.

The paper pulp used for high-class goods consists of pure wood cellulose, while for the commoner qualities mechanical wood pulp, waste papers, and any similar fibrous material are employed.

The mineral substances used are china clay, chalk, gypsum, barytes, ochre, sienna, and other mineral pigments.

The adhesive materials are glue, casein, gum, starch, paste, dextrine, Iceland moss, or wax.

For experimental purposes, small quantities of papier-mâché may be prepared in the following manner:—

When old newspapers or brown papers are used as the fibrous basis of the papier-mâché, they are first torn up into small pieces, moistened with hot water, tied up in a small cloth bag or sack, which must only be half filled, and then immersed in a basin of warm water and thoroughly kneaded by hand, so that the paper is gradually reduced to the condition of pulp. If the kneading process is carried out thoroughly the paper is entirely reduced to pulp. The excess of water can be removed by pressure and the preparation of the final mixture completed by the incorporation of clay, pigment, and adhesive.

In the preparation of papier-mâché for goods on a large scale a beating engine is used in order to break up the old paper or wood pulp into a fibrous condition.

The following formulæ can be used for making papier-mâché:—


(1)		(2)		(3)		(4)

Pulp	22	Pulp	22	Pulp	12	Pulp	33
Clay	37	Chalk	30	Rosin size	22	Starch	9
Casein	37	Glue	4	Flour	11	Clay	9
Water	4	Water	44	China clay	11	Water	49
				Water	44

	100		100		100		100

Plaster Moulds.—Plaster of Paris or gypsum is the main article used for moulds and pattern. The preparation of gypsum for casting is made as follows:—The gypsum is gradually worked up into a creamy paste with water, the mixing being done quickly yet thoroughly.

The pattern of which it is desired to form a mould must be coated with oil. Around the pattern placed on a table a wall of wood or pasteboard is fixed, so that a basin will be formed of suitable depth, preventing the gypsum from flowing away. Patterns of figures or of curved articles have to be made in two or more parts. For that purpose the pattern is usually cut into two pieces. Two moulds are now readily obtainable by first oiling the pattern and by pouring the gypsum in a thin state gradually over the surface, to avoid the forming of air bubbles.

The rapid drying of the soaked gypsum is sometimes inconvenient, but the addition of a saturated solution of borax in water to the gypsum mixture can be resorted to as a check.

Various means are employed for hardening and strengthening the plaster cast, such as the addition of coarse paper fibres, shreds of canvas, iron filings, or wire.

Colouring.—Usually a cheap water colour only is required; a light coating of a cheap varnish may be sufficient. In other cases a water colour serving as a filler for smoothing the surface may receive a finish of one or more coats of resinous solutions in alcohol or of copal varnish. Many goods are coated with asphaltum or Japan varnish and dried in cold or hot air.

Some of the articles may be decorated with scrolls or arabesques in oil colours or enamels, or the lines may be covered with bronze powder, or with metal, gold, or aluminium leaf.

Varnishing.—The following varnish recipes are suitable:—


(1)		(2)		(3)		(4)

Shellac	20	Shellac	10	Shellac	6	Sandarac	15
Alcohol	70	Rosin	10	Sandarac	3	Mastic	5
Lamp black	10	Alcohol	60	Mastic	18	Turpentine	5
		Lamp black	20	Alcohol	73	Alcohol	75

	100		100		100		100

[CHAPTER VIII]
CHEMICALS USED IN PAPER-MAKING

The manufacture of paper is a highly technical industry, which requires a practical knowledge of mechanical engineering, as well as an intimate acquaintance with the many important chemical problems connected with the art.

The following brief description of the various chemicals used in the manufacture of paper is divided into certain classes, based upon the order of the operations through which the raw material passes before its final conversion into paper:—

(1) The alkaline processes used for treating raw fibre: soda ash; caustic soda; lime; recovered ash.

(2) The conversion of wood into sulphite pulp: sulphur; limestone.

(3) The operation of bleaching: bleaching powder; antichlors; acids.

(4) The sizing and loading of paper: casein; gelatine; rosin size; alum; starch; silicate of soda; pigments and soluble dyes; mordants.

Mineral substances for loading: clay, blanc fixe, etc.

Carbonate of Soda.—This substance, also known under the trade names of alkali and soda ash, is used in the paper mill for the manufacture of caustic soda. It is purchased by the paper-maker from the chemical works, and used together with the recovered ash (see page [78]) for the production of caustic soda solution, which is required in the treatment of raw fibres.

It is also used for the preparation of rosin size (see “Rosin Size”) and in softening hard waters for steam-raising purposes.

Sodium Carbonate Table.

Showing percentage by weight and pounds per 100 gallons in solutions of various densities.


Twaddell.	Percentage by Weight.		100 gallons contain pounds of

	Na₂O.	Na₂CO₃.	Na₂O.	Na₂CO₃.	48 per cent. Ash.

1	0·28	0·47	2·76	4·72	5·74
2	0·56	0·95	5·61	9·60	11·68
3	0·84	1·42	8·42	14·41	17·56
4	1·11	1·90	11·34	19·38	23·64
5	1·39	2·38	14·26	24·40	29·73
6	1·67	2·85	17·10	29·36	35·77
7	1·95	3·33	20·16	34·46	42·00
8	2·22	3·80	23·12	39·52	48·15
9	2·50	4·28	26·17	44·72	54·50
10	2·78	4·76	29·71	50·00	60·90
11	3·06	5·23	32·27	55·18	67·22
12	3·34	5·71	35·36	60·50	73·72
13	3·61	6·17	38·43	65·72	80·07
14	3·88	6·64	41·57	71·06	86·58
15	4·16	7·10	44·65	76·33	93·03
16	4·42	7·57	47·80	81·77	99·61
17	4·70	8·04	51·02	87·24	106·31
18	4·97	8·51	54·25	92·74	113·10
19	5·24	8·97	57·45	98·26	119·70
20	5·52	9·43	60·67	103·70	126·42
21	5·79	9·90	63·98	109·40	133·45
22	6·06	10·37	67·32	115·10	140·12
23	6·33	10·83	70·63	120·81	147·10
24	6·61	11·30	74·00	126·62	154·20
25	6·88	11·76	77·38	132·30	161·12
26	7·15	12·23	80·83	138·20	168·51
27	7·42	12·70	84·31	144·12	175·70
28	7·70	13·16	87·67	150·20	182·70
29	7·97	13·63	91·28	156·15	190·14
30	8·24	14·09	94·77	162·00	197·40

Analysis.—The value of soda ash, carbonate of soda, and recovered ash depends on the amount of available alkali (Na₂O) present.

A weighed quantity (15·5 grammes conveniently) is dissolved in a measured volume of distilled water (500 c.c.), and titrated with standard normal hydrochloric acid, methyl orange indicator being used.

Caustic Soda.—Raw vegetable fibres may be reduced to the condition of paper pulp by treatment with caustic soda. In practice this process is largely resorted to for the manufacture of pulp from esparto, straw, and wood, the spent caustic soda being recovered and used again.

The paper-maker prepares the caustic required for digesting the raw material from recovered ash and carbonate of soda.

A convenient volume of clear liquor obtained by lixiviating the recovered ash is boiled with lime in suitable causticising pans, the reaction being represented as follows:—

Na₂CO₃	+	CaO	+	H₂O	=	2 NaOH	+	CaCO₃.
Soda ash	+	Lime	+	Water	=	Caustic soda	+	Chalk.

According to this equation, 100 lbs. of soda ash require 53 lbs. of quicklime, but a slight excess is generally added, 58 or 60 lbs. being the usual amount actually employed. Several precautions should be observed in the process of causticising.

(1) The liquor from the recovered soda should be bright and clear, indicating complete incineration of the ash.

(2) The liquor is best causticised at a density between 1·050 and 1·100 (10-20, Twaddell). With stronger solutions the reaction is complicated and the yield of caustic soda reduced. Lunge has shown that if the density of the solution is 1·025 the proportion of soda causticised is 99·5 per cent., whereas at a density of 1·150 it is only 94·5 per cent. In the latter case the caustic soda formed acts upon the chalk produced and is reconverted into carbonate.

(3) The large quantities of chalk residue resulting from the reaction must be thoroughly and carefully washed. The economy of the whole process depends in no small measure upon this seemingly small detail.

Caustic Soda Tables.

Showing quantity of liquor obtained from 1 cwt. of caustic soda and the amount of caustic soda in 100 gallons of liquor (adapted from Lunge and others).


Twaddell.	Gallons obtained per hundredweight of Caustic.		Twaddell.	Pounds of Caustic Soda per 100 gallons Liquor.

	60 per cent. Caustic.	77 per cent. Caustic Pure.		60 per cent. Caustic.	77 per cent. Caustic Pure.

1	1,777	2,358	1	6·3	4·75
2	896	1,179	2	12·5	9·5
3	596	767	3	18·8	14·6
4	448	574	4	25·0	19·5
5	359	457	5	31·2	24·5
6	298	384	6	37·6	29·2
7	256	330	7	43·8	34·0
8	223	287	8	50·1	39·0
9	199	256	9	56·2	43·7
10	178	229	10	62·9	48·9
11	162	208	11	69·1	53·7
12	148	190	12	75·7	58·7
13	136	176	13	82·1	63·7
14	126	166	14	88·5	67·5
15	117·5	152	15	95·0	73·5
16	110	141·5	16	101·5	79·0
17	103·5	135	17	107·8	83·0
18	98	125·5	18	114·4	89·0
19	92·8	119·5	19	120·8	93·8
20	88	114	20	127·2	98·0
25	70	90·3	25	159·5	124·0
30	56·5	73	30	197·3	153·0
35	48	61·5	35	234·9	182·2
40	41	53	40	272·6	211·6
45	35·3	45·5	45	317·4	246·3
50	31	40	50	362·1	281·0

Dilution Table for Strong Liquors.

Showing number of gallons of water required to reduce the density of 100 gallons of liquor from a higher density, D, to a lower density, d. (See page [163]).


Higher Density, D (Twaddell).	Lower Density, d.

	14.	13.	12.	11.	10.	9.	8.	7.	6.	5.	4.

42	200	223	250	281·8	320	367	425	500	600	740	950
40	185	207	233·3	263·6	300	344·4	400	471·4	566·6	700	900
38	171	192	216·6	245·5	280	322·2	375	442·8	533·3	660	850
36	157	177	200	227·3	260	300	350	414·3	500	620	800
34	143	161·5	183·3	209·1	240	277·7	325	385·7	466·6	580	750
32	128·6	146	166·6	191	220	255·5	300	357·1	433·3	540	700
30	114·3	130·6	150	172·8	200	233·3	275	328·5	400	500	650
28	100	115·3	133·3	154·6	180	211·1	250	300	366·6	460	600
26	85·7	100	116·6	136·4	160	188·8	225	271·4	333·3	420	550
24	71·4	84·6	100	118·2	140	166·6	200	243	300	380	500
22	57·1	69·2	83·3	100	120	144·4	175	214·4	266·6	340	450
20	43	53·6	66·6	81·8	100	122·2	150	185·7	233·3	300	400
18	28·6	38·4	50	63·7	80	100	125	157	200	260	350
16	14·3	23	33·3	45·5	60	77·7	100	128·5	166·6	220	300

Lime and Limestone.—Carbonate of soda and recovered ash are converted into caustic soda by means of lime. About sixty parts of lime are necessary for the conversion of 100 parts of carbonate of soda. Large quantities of insoluble carbonate of lime are produced in this operation, and great care is necessary to prevent a loss of caustic soda which occurs if the residue is not thoroughly washed. In some cases the residual chalk is drained by vacuum filters in order to remove all traces of soluble alkali. Processes have been devised for calcining the residue so as to convert the carbonate into caustic lime to be used over again, but no economical and practical method has yet been found. The treatment of the residual chalk with sulphuric acid for the production of calcium sulphate appears feasible, but the substance obtained is very impure, and therefore has little commercial value.

Limestone is required in considerable quantity for the preparation of sulphite of lime for the manufacture of wood pulp.

Recovered Ash.—The black liquor obtained during the process of the boiling of straw, esparto, and other paper-making fibres contains a large proportion of non-fibrous organic constituents derived from the fibres, the quantity of which may be gauged from the fact that these fibres generally lose 50 per cent. of their weight when being boiled. The black liquor on evaporation yields a thick resinous mass, which is converted into carbonate of soda when burnt.

Advantage is taken of this fact to carry out a process of incineration on a large scale, so that heat derived from the burning off of the resinous mass is utilised for evaporation of weaker liquors. The ash is drawn from special furnaces, put aside, and allowed to char quietly, so that the carbonaceous matter is more or less completely burnt away. The ash in this form contains about 40 per cent. of soda, its composition being determined by the nature of the fibre which has been treated. In the case of straw, the amount of silicate is considerable, as shown by the following typical analysis:—

Sodium carbonate	70·2
Sodium hydrate	2·3
Sodium sulphate	4·1
Sodium chloride	7·5
Silica	7·5
Oxides of iron and alumina	0·75
Unburnt carbon, etc.	7·65

	100·00

At the present time there is no process in general use for the recovery of the liquors used in the treatment of wood by the sulphite process. Many schemes have been proposed, the most promising of which is that of Drewsen.

Sulphur and Sulphites.—The pale yellow brittle substance known as sulphur is too familiar to require any detailed description. It unites with oxygen in various proportions, and these in contact with water form the various sulphur acids known to commerce. Sulphur burned with a limited quantity of air forms sulphurous acid gas, and this substance is the chief product of oxidation, which by further treatment can be converted into sulphites.

In the manufacture of the sulphur compounds required in the preparation of wood pulp, the furnace for burning the sulphur consists of a flat-bottomed cast iron retort which is very shallow, and provided with a curved top, to which a pipe is fixed, so that the sulphurous acid may be conveyed away from the furnace. In the most recent form of sulphur oven a small conical-shaped revolving furnace is employed, which produces a satisfactory gas of constant composition very economically.

Bisulphite of Lime.—This compound is obtained when the sulphurous acid gas is brought into contact with moistened limestone. In the manufacture of bisulphite of lime on a large scale the sulphurous acid gas is drawn or pumped up tall circular towers filled with blocks of limestone, kept moistened by a carefully regulated stream of water flowing from the top of the tower.

In another system known as the acid tank process, the gas is forced into large circular vats containing milk of lime.

In either case a solution is prepared containing bisulphite of lime, together with a certain proportion of free sulphurous acid, the object of the pulp manufacturer being to obtain a solution containing as large a proportion of free sulphurous acid as possible. The composition of a solution will vary on this account, and the following may be quoted as being an example of such a liquor:—

Free sulphurous acid	3·23	per	cent.
Combined sulphurous acid	0·77	„	„

	4·00	„	„

For experimental purposes the bisulphite of lime solution may be prepared by passing sulphurous acid gas into a mixture of water and sulphite of lime. The latter compound is insoluble in water, but gradually dissolves when the gas is absorbed. A known weight of sulphite of lime is added to a measured volume of water, and the sulphurous acid gas discharged into the mixture from a siphon of compressed sulphurous acid. The amount of gas absorbed is determined by weighing the siphon before and after use, the loss of weight representing the gas discharged.

The following figures may be quoted as an example:—

	Quantities	used.
Calcium sulphite	536	grammes.
Water	7100	c.c.
Gas absorbed	534	grammes.
Density of solution	18°	Twaddell.

The composition of the solution prepared is—

Combined sulphurous acid	3·50
Free sulphurous acid	6·54
Lime	3·06
Water	86·90

	100·00

Analysis.—The examination of sulphite liquors for free and combined sulphurous acid is made by means of standard iodine solution and normal caustic soda solution.

A known volume of the sulphite liquor is first titrated with standard iodine solution, the number of cubic centimetres required being a measure of the total sulphurous acid.

Each cubic centimetre standard iodine solution = ·0032 grammes SO₂. The titrated liquor is then treated with standard caustic soda in quantity sufficient to exactly neutralise the acid. The volume of caustic soda solution used minus the number of cubic centimetres of iodine first added is a measure of the free sulphurous acid.

Bleaching Powder.—This substance is prepared on a large scale by allowing chlorine gas to act upon dry slaked lime. The lime absorbs nearly one-half its weight of chlorine and forms a dry white powder, having a very pungent odour. The best bleaching powder contains about 37 per cent. of what is termed “available chlorine.” The substance, on being treated with water, gives a greenish-coloured solution known as bleach liquor, and when raw paper-making material, after having been digested with caustic soda, is treated with this solution, it is gradually bleached to a white colour. The composition of the powder may be represented approximately as follows:—

Available chlorine (combined with lime)	36·00
Chlorine in the form of chloride	0·32
Chlorine in the form of chlorate	0·26
Lime	44·66
Magnesia	0·43
Silica, iron oxides, etc.	1·33
Insoluble matter	17·00

	100·00

Since the amount of bleach used for wood pulps varies from 8 per cent. to 25 per cent. of powder on the dry wood pulp, the cost of bleaching in some cases is considerable. The economy of the process depends in some measure upon the care exercised in the purchase of bleaching powder of standard quality, the storage of same in a dark, cool place, and the efficient treatment or exhaustion of the powder when the bleach liquor is prepared.

The powder is usually agitated for about an hour with water sufficient to produce a liquor of 13°-15° Twaddell. The undissolved powder is allowed to settle and the clear solution siphoned off, after which the sediment is washed once or twice to remove all the soluble matter completely.

Bleach Liquor Table.

Showing for bleaching powder solutions of known density the quantity of powder necessary to produce 100 gallons of liquor and the number of gallons obtained from 1 cwt. of powder (adapted from Lunge and Beichofen).


Twaddell.	Available Chlorine Pounds per 100 gallons.	Number of Gallons obtained from 112 lbs. of Powder.		Pounds of Powder per 100 gallons of Liquor.

		34 per cent. Powder.	35 per cent. Powder.	34 per cent. Powder.	35 per cent. Powder.

0·25	0·70	5,464	5,600	2·05	2·00
0·50	1·40	2,725	2,800	4·11	4·00
1	2·71	1,405	1,445	7·97	7·74
2	5·58	681	702	16·41	15·94
3	8·48	448	462	24·95	24·23
4	11·41	334	340	33·55	32·60
5	14·47	264	270	42·58	41·34
6	17·36	219·5	225	51·06	49·60
7	20·44	186	191	60·11	58·40
8	23·75	160	165	69·85	67·85
9	26·62	141	147	78·30	76·57
10	29·60	129	132·5	87·06	84·54
11	32·68	116·5	120	96·11	93·37
12	35·81	106·5	109·5	105·32	102·31
13	39·10	98	100	115·00	111·70
14	42·31	90	92·5	124·45	120·90
15	45·70	84	86	134·41	130·56
16	48·96	78	80	143·80	139·71
17	52·27	73·5	75	153·53	149·34
18	55·18	69	71	162·30	157·65
19	58·40	65·5	67	171·00	166·86
20	61·50	61·5	64	180·88	175·71

The best method for extracting powder is to agitate the material with water for a short period, and to stop the mixing process directly the maximum density has been obtained, which usually takes place in 15 minutes. Prolonged agitating prevents the powder from settling readily.

The maximum quantities of liquor which can be obtained from bleaching powder are shown on page [162]. The following table is useful as showing the amount of water required for diluting strong liquors, the figures being applicable to any solution independent of the nature of the dissolved substance.

Dilution Table for Weak Liquors.

Showing number of gallons of water required to reduce the density of 100 gallons of liquor from a higher density, D, to a lower density, d. (See page [157].)


Higher Density, D (Twaddell).	Lower Density, d.

	12.	11.	10.	9.	8.	7.	6.	5.	4.	3.	2.	1.

16	33·3	45·4	60	77·7	100	128·5	166·6	220	300	433·3	700	1,500
15	25·0	36·4	50	66·6	87·5	114·3	150	200	275	400	650	1,400
14	16·6	27·3	40	55·5	75	100	133·3	180	250	366·6	600	1,300
13	8·3	18·2	30	44·4	62·5	85·7	116·6	160	225	333·3	550	1,200
12		9·1	20	33·3	50	71·4	100	140	200	300	500	1,100
11			10	22·2	37·5	57·1	83·3	120	175	266·6	450	1,000
10				11·1	25	42·8	66·6	100	150	233·3	400	900
9					12·5	28·5	50	80	125	200	350	800
8						14·2	33·3	60	100	166·6	300	700
7							16·6	40	75	133·3	250	600
6								20	50	100	200	500
5									25	66·6	150	400
4										33·3	100	300

Antichlors.—The residues of chlorine which may be left in pulp after bleaching are frequently neutralised by the use of substances termed antichlors, which react with the calcium hypochlorite, converting it into chlorides.

The sodium hyposulphite is the most frequently used antichlor, the reaction between this and hypochlorite resulting in the formation of calcium sulphate and sodium chloride; 100 lbs. of commercial bleaching powder will require 30 lbs. of crystallised sodium hyposulphite.

The sulphites of soda and lime also act as antichlors, reducing the hypochlorite of calcium into sulphate of lime or soda. The chief advantage of the use of sulphites is to be found in the fact that the substances obtained by the reaction are neutral.

The best practice in bleaching is to avoid the necessity for using any forms of antichlors by careful regulation of the bleaching process. It has already been suggested in previous references to bleaching that the desired results are obtained when the pulp and bleach are left in contact with one another in tanks or drainers until the bleach is completely exhausted, the residual salts in solution being removed by thorough washing.

Gelatine.—For animal-sized or tub-sized papers gelatine is used. It can be prepared by the paper-maker from hide clippings, sheep skins, bone, etc., or can be purchased ready made.

Beadle gives the following interesting details as to the amount of gelatine which can be obtained from wet hide pieces:—

Weight of Wet Hide Pieces, 2,128 lbs.


Draught.	Gallons.	Per cent. Gelatine in Solution.	Weight of Gelatine. Lbs.

1	126·48	6·775	85·64
2	128·96	6·052	78·04
3 and 4 mixed	135·20	9·446	127·63

Total	390·64		291·31

Percentage of gelatine on weight of wet skins = 13·69.

A similar trial on the same class of wet hide pieces gave a yield of 13·23 per cent.

Two trials, of a somewhat different class of wet hide pieces, gave respectively 13·11 and 12·8 per cent.

The temperature of the draught water should be approximately as follows:—


Draught.	At Beginning.	At End.

1	120° F.	150° F.
2	130° F.	160° F.
3 and 4	140° F.	180° F.

In the final draught it is often necessary to use live steam at the finish, but this should be avoided if possible.

The water contained in wet hide pieces varies from 77 to 90 per cent. in the different pieces, but in the bulk the average may be taken at 85 per cent.

Casein.—Casein is the nitrogenous principle of milk, and belongs to the class of proteids which are definite compounds of oxygen, hydrogen, carbon, and nitrogen, forming the basis of the most important constituents of all animal fibres, albumen, casein, and gluten. A very pure form of casein is cheese made from skimmed milk. Casein belongs to that class of albumens which are soluble in water, e.g., egg albumen, blood albumen or serum, and lactalbumen, or milk albumen; these are mostly precipitated from solution by saturation with sodium chloride (common salt) or magnesium sulphate; but they are all coagulated by heat.

By the action of rennet on milk the proteid or albumen principle is converted into a curd (casein). This curd, when freed from fats, is insoluble in water, but is soluble in dilute acids, or alkalies, or alkaline carbonates, from which substances, however, it is reprecipitated by acidulation. Instead of the above method, casein may be precipitated from milk by saturation with sulphate of magnesia, and washing the precipitate with a solution of that salt until the washings contain no albumen, and then redissolving the prepared casein by adding water. The salt still adhering to the precipitate enables it to dissolve. On a large scale the casein is usually prepared by treating the milk with acid.

Casein is readily dissolved by alkalies and alkaline carbonates, borax, boracic acid solution, caustic soda, and bicarbonate of soda.

Starch.—This substance is used in many classes of paper for improving the surface and finish. It is added to the pulp in the beating engine in the dry form as powder, or in the form of starch paste, produced by boiling the starch in water.

The viscosity of the starch paste is somewhat increased by the addition of a small quantity of alkali, but due care must be exercised in boiling, which should only be carried out sufficiently to cause the starch granules to burst, as any excessive boiling causes the starch paste to lose some of its viscosity.

The presence of starch in paper is detected by the blue coloration produced when the paper is dipped into a weak solution of iodine. The determination of the exact percentage of starch in a paper is a matter of some difficulty.

Silicate of Soda.—The precipitation of gelatinous silica upon the pulp in the beating engine is generally regarded as favourable to the production of a sheet of paper having what is known as a harder finish. The precipitation is effected by adding a solution of silicate of soda to the beating engine, with the subsequent addition of sufficient sulphate of alumina to react with the silicate of soda.

Analysis of Commercial Alums.

(Griffin and Little.)


—	(1)	(2)	(3)	(4)

Insoluble in water	0·05	10·61	0·11	0·56
Alumina (Al₂O₃)	15·47	14·96	11·64	16·58
Iron protoxide (FeO)	0·02	0·13	0·06	—
Iron sesquioxide (Fe₂O₃)	0·00	1·08	1·17	0·04
Zinc oxide (ZnO)	—	—	—	—
Soda (Na₂O)	1·72	0·57	4·75	0·56
Magnesia (MgO)	—	—	0·45	—
Sulphuric acid (SO₃) combined	37·26	37·36	35·98	39·17
Sulphuric acid (SO₃) free	—	1·08	5·13	—
Water by difference	45·48	34·21	40·71	43·09

	100·00	100·00	100·00	100·00

Sizing test (parts of dry neutral rosin size precipitated by one part of the alum)	3·32	3·47	3·19	3·71

Table showing Value of Solutions of Aluminium Sulphate.


Twaddell.	Pounds per 100 gallons.

	Al₂O₃.	SO₃.	Sulphate of Alumina containing 15 per cent. Al₂O₃.

1	1·4	3·3	9·0
2	2·8	6·5	19·0
3	4·2	9·8	28·0
4	5·6	13·0	37·0
5	7·0	16·3	47·0
6	8·4	19·6	56·0
7	9·8	22·8	65·0
8	11·2	26·1	75·0
9	12·6	29·4	84·0
10	14·0	32·6	93·0
11	15·4	35·9	103·0
12	16·8	39·1	112·0
14	20·3	47·3	135·0
16	23·1	53·8	155·0
18	26·2	60·3	172·0
20	29·4	68·5	196·0
25	37·1	86·5	247·0
30	44·8	104·4	299·0
35	53·2	124·0	355·0
40	60·9	142·0	405·0
45	68·6	159·9	456·0
50	77·7	181·0	578·0
55	86·1	200·6	575·0
60	95·2	221·8	635·0

Alum.—Alum is one of the most important substances required in the manufacture of paper, its chief function relating to the sizing of paper. Various forms are utilised for this purpose, the purest being sulphate of alumina, required for high grade papers, and the cheaper form known as alum cake, for news and common printing.

The alum is manufactured on a large scale by heating china clay or bauxite with sulphuric acid. This reaction gives sulphate of alumina together with silica. If the mass is heated to dryness, it is sold under the name of alum cake. If the mass is extracted with hot water and the insoluble silica filtered off, the solution can be evaporated down for the production of sulphate of alumina, which is sold in the form of large cakes or in the form of crystals.

By careful selection of raw material a sulphate of alumina can be prepared almost entirely free from iron. The presence of the latter is undesirable, since on exposure to air the sulphate of iron produced during the manufacture of the alum is slowly oxidised and turns brown. Ultimately this affects the colour of the finished paper.

Alum is added to solutions of animal size or gelatine in order to thicken the solution and render it more viscous. It also acts as a preservative, and is used for regulating the absorption of the gelatine by the paper, the penetration effects being materially varied by the extent to which the alum is utilised.

In the process of engine sizing, a term applied to the application of rosin size on account of the fact that the process is completed in the beating engine, alum plays an important part. The mere addition of the prepared rosin soap to the mixture of pulp and water in the beating engine does not size the paper, but the alum precipitates the rosin from its solution, producing a complex mixture said to consist of resinate of alumina and free rosin particles, and subsequently the heat of the paper machine drying cylinders renders the paper more or less impermeable to moisture.

The appearance and tone of paper, more particularly of coloured papers, are brightened by the use of an excess of alum over and above that necessary to precipitate the rosin soap.

Rosin Size.—This substance is used chiefly for the sizing of news and cheap printing papers, and is also employed together with gelatine for the commoner writing papers. It is prepared by boiling rosin with carbonate of soda under various conditions.

Rosin, sometimes called colophony, is obtained from the sap of certain firs and pine trees. This on distillation yields spirits of turpentine, leaving behind as a residue the mixture of substances to which is given the name rosin. It behaves as an acid, and therefore will combine with certain alkaline oxides, producing soluble resinates.

The nature of the rosin soap used in the paper mill varies according to the conditions under which the size is prepared. If a large proportion of rosin is used, then the size obtained consists of a mixture of resinate of soda together with free rosin dissolved in the solution. If the proportion of rosin is small compared with the amount of carbonate of soda, the composition of the final mixture is quite different. The difference in treatment results in the formation of—

(A) Neutral Size, prepared by boiling a known weight of rosin with sufficient alkali to combine with it and form a neutral resinate of soda. Theoretically this may be obtained by using 630 parts of rosin to 100 parts of soda ash. It is doubtful how far the reaction is completed so as to produce an exactly neutral solution containing only resinate of soda.

(B) Acid Size.—When the proportion of rosin is largely increased the soda becomes converted into the alkaline resinate, and the excess of rosin is gradually dissolved in the resinate formed.

The practical operations necessary for the preparation of the size are comparatively simple. In the case of size containing relatively small percentages of free rosin, the boiling is conducted in open vessels, but for the manufacture of rosin size containing large proportions of free rosin boiling under pressure in closed vessels must be resorted to.

With the open pan process a steam jacketed pan is used, and the required quantity of alkali, dissolved in water, is placed therein and heated to boiling point. The rosin well powdered is added in small quantities from time to time, this being effected cautiously in order that the carbonic acid gas set free during the process may readily escape. The rosin is generally completely saponified after four or five hours' boiling. It is then passed through strainers into store tanks, from which it is drawn into the beating engines as required.

In the case of rosin boiled under pressure a cylindrical vessel provided with a manhole at the top is used. The correct amounts of alkali and water are put into the digester, and also the rosin in a powdered form, the digester being fitted with a perforated plate placed about two feet above the bottom of the vessel in order to prevent the rosin forming into a hard mass at the bottom of the digester.

It is possible in this way to manufacture a thick size containing 30 or 40 per cent. of free rosin and a comparatively small proportion of water. Many paper mill firms prefer to purchase such size ready made.

The most recent modification of the ordinary rosin size is a compound prepared by treating rosin with silicate of soda. This alkali dissolves rosin readily, and the soap obtained when suitably diluted with water decomposes in the beating engine on the addition of aluminium sulphate, with the precipitation of a gelatinous silica which assists in hardening the paper.

Bacon has patented a process in which powdered rosin is melted down with dry crystalline silicate of soda. The resultant product is ground to a fine powder, which is then ready for use. It dissolves easily in water, and when decomposed with the proper proportion of alum gives a gelatinous viscous mass said to have excellent sizing properties.

The advantages of a dry powdered rosin size readily soluble in water are obvious.

Loading.—The term “loading” is applied to the various substances which are employed for the purpose, as it is commonly supposed, of making paper heavy. But china clay and similar materials are not added simply in order to give weight to the paper, since they serve to produce opacity and to improve the surface of papers which could not be satisfactorily made unless such materials were used.

Examination of Paper for Loading.—If a piece of paper is crumpled up, placed in a small crucible, and then ignited until all the carbonaceous matter has been burnt off, a residue is left in the crucible which may be white or coloured. This is usually termed the ash of the paper. The amount of ash present is determined by taking a weighed quantity of paper and weighing the residue obtained. Special appliances can be obtained for making rapid determinations of the ash in paper, but for occasional analyses they are not required.

China Clay.—This is the best known and most commonly used loading. The purest form of this material is kaolin, a natural substance formed by the gradual decomposition of felspathic rocks arising from exposure to the long-continued action of air and water. The clay occurs in great abundance in Dorset, Cornwall, and Devon, the southern counties in England, where the most famous deposits are found.

The natural mineral is levigated with water, and the mixture allowed to flow through a series of settling ponds, so that the clay gradually settles in the form of a fine deposit. The clay is dried and packed in bags. Its value is controlled largely by the purity of its colour and its freedom from grit and sand. It is essentially a silicate of alumina, having the approximate composition—

Silica (SiO₂)	43·00
Alumina (Al₂O₃)	35·00
Combined water	10·00
Moisture and impurities	12·00

	100·00

The specific gravity of the dry substance is 2·50.

It is utilised as a loading in all kinds of paper, and forms also the main ingredient in the coating found on ordinary art and chromo papers.

Ash containing China Clay.—In news, cheap printings, and common art papers the ash almost invariably contains china clay. This substance is insoluble in dilute acids, but is acted upon by concentrated sulphuric acid when digested for some time. A simple test for the presence of china clay in ash is the blue coloration which is obtained when the ash after being ignited is gradually heated with a few drops of solution of cobalt nitrate. China clay can be decomposed by fusion with carbonate of soda in a crucible. By this means silicate of alumina is decomposed, and the alumina goes into solution, the silica remaining as an insoluble residue. The filtered solution is boiled with an excess of ammonia which gives a gelatinous precipitate of aluminium hydrate.

Sulphate of Lime.—This compound is valued chiefly for its brilliancy of colour, being used in high-class papers. It is slightly soluble in water, to the extent of about 23 lbs. in 1,000 gallons, and this fact must be taken into account when the material is added to the pulp in the beating engine.

It occurs naturally in a variety of forms, such as gypsum, alabaster, selenite, the first of which when finely powdered is sold to the paper-maker as gypsum, powdered plaster, and under other fancy names.

It can be prepared artificially by adding sulphuric acid to solutions of calcium salts; and the precipitated product so obtained is sold as terra alba, pearl hardening, satinite, mineral white, etc.

The tests for sulphate of lime in paper ash are based upon the following reactions:—

Calcium sulphate is soluble in dilute hydrochloric acid. The addition of a few drops of barium chloride to the solution produces a dense heavy precipitate, indicating the sulphate. A small quantity of ammonium oxalate solution added to another portion of the dissolved calcium salt previously neutralised with ammonia produces a precipitate and indicates calcium.

A microscopic test of paper for the presence of sulphate of lime is based upon the slight solubility of the salt in water. The paper is boiled with some distilled water. The water is evaporated to a small bulk and transferred to a glass slip, and the gradual formation of characteristic sulphate of lime crystals can be seen by means of the microscope as the water cools down.

French Chalk.—This material is prepared by grinding talc into a fine powder, and possesses a good colour and a somewhat soapy feel. It is a silicate of magnesia, having the approximate composition—

Silica (SiO₂)	62·00
Magnesia (MgO)	33·00
Water	4·30
Traces of oxides, etc.	0·70

	100·00

Other silicates of magnesia used for paper-making are agalite and asbestine, the latter being a finely ground asbestos.

The composition of asbestos is approximately—


—	Italian.	Canadian.

Lime and magnesia	38·0	33·0
Silica	42·0	41·0
Oxides of iron and alumina	5·0	12·0
Total water	13·0	12·0
Traces of soda, etc	2·0	3·0

	100·00	100·00

[CHAPTER IX]
THE PROCESS OF BEATING

Introduction.—The process of beating has for its object the complete breaking down of the bleached pulp to the condition of single fibres, and the further reduction of the fibres, when necessary, into smaller pieces. The disintegration of the material is essential for the production of a close even sheet of paper, and the amount of beating required varies greatly according to the nature of the raw material, and the class of paper to be produced.

The textile trade, on the other hand, depends on a raw material composed of strong fibres, or of filaments characterised by great length, and any processes of treatment which tend to reduce the length of such fibres are carefully avoided, and it is therefore obvious that fibres which are of no value for textile purposes can be appropriated for paper-making.

Condition of Fibres.—The great differences in the physical characteristics and structure of the fibres employed for paper-making suggest that the possible variations in the final product obtained by beating are very numerous. This is a well-known fact, and it is further to be noted that this mechanical operation brings about not merely alterations of a physical order, but introduces some interesting and important chemical changes.

Of the better-known materials linen, with an average fibre length of 28 mm., the structure of which lends itself to considerable alteration by beating, is in marked contrast to esparto, the fibre length of which is only 1·5 mm. If the process of beating a linen rag merely resulted in the cutting of all the fibres of 28 mm. long into short fragments of 1·5 mm., there would be nothing remarkable in it, but the changes which occur in reducing the long linen fibre to 1·5 or 2·0 mm. are of a far more important character than this.

Early Methods.—In the early days of paper-making the disintegration of the half-stuff was effected by a true “beating” process, the rags being subjected to the action of heavy stampers, which broke up the mass of tangled fibre into a uniform pulp. The fibres for the most part retained their maximum length in this operation, which was exceedingly slow and tedious, though at the same time giving a sheet of paper of remarkable strength.

The nearest imitation of these old-time rag papers is to be seen in the well-known Japanese papers, which are extraordinarily strong. Some of these the writer has examined in order to determine the length of the fibre. The sheets when held up to the light appear “cloudy” and “wild” owing to the presence of the long fibres, which have only been separated or teased out by the primitive methods of beating used, and not completely disintegrated.

Conditions of Beating.—About A.D. 1700 there began a great epoch in the history of paper-making. With the invention of the Hollander engine about A.D. 1670, the process of disintegration was greatly hastened, because it was possible to reduce the half-stuff much more readily. The substitution of the idea of plain “beating” by a principle which combined the gradual isolation of the individual fibres with a splitting up of those fibres lengthwise and crosswise was not only an advantage in point of economy of time and cost, but also a material advance in the possibilities of greater variations in the finished paper.

The conditions of the process of beating carried out with a Hollander permit of considerable alteration, so that these changes in the fibre are not surprising when properly understood. In fact, it is now conceded that a close study of the theory and practice of beating is likely to bring about still more remarkable improvements in this important department of the paper-maker's work. The quality and character of the paper made may be varied with—

(1) The origin of the raw material, e.g., rags, esparto, or wood;

(2) The condition of the material, e.g., old or new rags, green or mature esparto, mechanical or chemical wood pulp;

(3) The time occupied in beating, e.g., four hours for an ordinary rag printing and twelve hours for a rag parchment;

(4) The state of the beater knives, e.g., sharp tackle for blottings and dull tackle for cartridge papers;

(5) The speed of the beater roll, also its weight;

(6) The rate at which the beater roll is lowered on to the bedplate;

(7) The temperature of the contents of the engine.

The Beater Roll.—If the beater roll is fitted with sharp knives, and this is put down close to the bedplate quickly, the fibres are cut up short, and they do not assimilate the water. If the roll is fitted with dull knives, or “tackle,” as it is sometimes called, and it is lowered gradually, the fibres are drawn and bruised out without being greatly shortened. In this condition the stuff becomes very “wet,” or “greasy,” as it is termed. The cellulose enters into association with water when beaten for many hours, and the pulp in the beating engine changes into a curious greasy-like mass of a semi-transparent character. Rag pulp beaten for a long time produces a hard, translucent, dense sheet of paper. Flax thread beaten 48 to 60 hours is used in practice for the manufacture of gramophone horns and similar purposes.

Soft porous papers like blottings, filtering papers, heavy chromos, litho papers, antiques, light printings, are made from pulps which are beaten quickly with the roll put down close to the bedplate soon after the stuff has been filled in.

With strong, dense, hard papers, such as parchments, banks, greaseproofs and the like, the pulp is beaten slowly and the roll lowered gradually.

The nature of the pulp and the time occupied in beating are also important factors in producing these different papers, three to four hours being ample for an ordinary wood pulp printing, whereas a wood pulp parchment requires seven to eight hours.

Beating Pulps Separately.—The use of esparto and wood pulp in conjunction with one another, or blended with rag, has introduced new problems into the question of beating. Perhaps the most important of these is the advisability of beating the pulps separately and eventually passing them through a mixer of some kind before discharging into a stuff chest. The necessity for differentiating the amount of beating is already partly recognised when very dissimilar pulps, such as strong rag and esparto, are blended, but the whole subject ought to be carefully studied by the paper-maker and investigated on its merits from the standpoint of “beating effects,” apart from questions of cost and expediency. The former fully understood and exhaustively examined by practical tests would of course only be developed if proved to be advantageous.

The field of research in this direction has not yet been seriously explored. With the enormous consumption of wood pulps of varying quality made from many different species of wood by several processes, there is ample room for interesting and profitable enquiry, particularly as the types of beating engine are so numerous. The effects produced by the Hollander, the refiner, the edge runner, the stone beater roll, and other mechanisms, are all of varying kinds.

Packing Papers.

[CHAPTER VIII]CHEMICALS USED IN PAPER-MAKING

[CHAPTER IX]THE PROCESS OF BEATING

[CHAPTER VIII]
CHEMICALS USED IN PAPER-MAKING

[CHAPTER IX]
THE PROCESS OF BEATING