GUTTA-PERCHA.
Gutta-percha is prepared by coagulation from the juice or sap of several trees, among others the Isonandra gutta, of Borneo and the East Indian Archipelago. The product gutta-percha is identical in composition with india rubber. It is hard at all ordinary temperatures.
Its manufacture includes purification and mastication. It is far more amenable to treatment than is india rubber. Many materials are mixed with it as adulterants or otherwise in the factories.
It is more useful in the form of sheets. These when heated to 122° F. (50° C.) become pliable and can be moulded by pressure to any degree. At the temperature of boiling water it becomes pasty and adhesive, and at 266° F. (130° C.) it is so soft that it may be considered as melted.
It is an admirable moulding material. Stereotypes and other relief or intaglio images can be made by pressing it while heated. These are often absolutely perfect reproductions of the original.
Dishes for photographic purposes, etc., are easily made out of the sheet. By gentle warming they become pliable, and a greater heat makes surfaces capable of adhering by pressure.
Tubes can be made by the squirting process, as used for india rubber. Wires are coated with it in a similar manner.
It has several defects. It is not durable if exposed to the air with consequent changes of temperature. It is also too easily softened by heat, as of course no hot liquid can be introduced into a gutta-percha vessel. The Parkes cold curing process can be applied to it, which makes it more indifferent to heat. This is applied by dipping an instant and drying. After several repetitions the period of dipping is prolonged and ultimately it is left immersed some time. If left immersed at first it would dissolve.
It is soluble in most caoutchouc solvents, particularly in carbon disulphide.
CHAPTER XIV.
GLUE OR COMPOSITION STAMPS.
Stamps made from a mixture of glue, glycerine, and molasses or from similar mixtures are an excellent substitute for india rubber stamps. Properly made they possess all the flexibility that characterizes the rubber ones, while for fatty inks such as that used by printers and lithographers, which inks tend to destroy rubber stamps, they are much better. They are adopted by the United States government for making dating stamps for use in the Post Office Department; by publishers of directories for printing advertisements on the edges of their publications, and in many other cases. Our description shall follow as closely as possible the process and methods used in the United States Post Office. They are there termed “composition blotters.”
The composition of which they are made is printer’s roller material. Nine and one-half pounds of fine quality glue are soaked in just enough soft water to cover it until it is thoroughly softened. It is then melted. In the Government Department a steam kettle is provided for the purpose. An ordinary glue pot will answer for smaller quantities. When melted four and one-half pounds of best molasses and seven pounds of glycerine are added, and the whole is thoroughly mixed. The formula varies a little according to the prevailing temperature, less molasses being added when the weather is warm, and vice versa. Experience is here the best teacher. When well mixed it is poured out into tin pails whose inner walls or sides and bottom have been rubbed over with oil. It solidifies in cooling and becomes a clear brown jelly quite free from any stickiness or superficial moistness.
Model for Composition Stamp Mould.
In use it is turned out of the pails to which, owing to the oiling, it does not adhere. It is cut off as wanted, melted by heat and cast in oiled moulds.
The latter are made of type metal to which one-third its weight of lead has been added. As model for the mould or matrix a brass model of the stamp is employed. This represents a sort of oval based cut-off or truncated cone, about an inch high and a little over an inch long on its base. A flange extends outward from its base and a tube is provided to fit this flange. Its smaller end corresponds to the face of the stamp, and on it are engraved in full relief any permanent characters, circles or border lines, etc. Through its centre one or more apertures are made. Into these, changeable steel, iron or brass type may be introduced and set fast with plaster of paris.
Composition Stamp Mould.
To make the mould, the brass model with its movable type set as required is placed upon a flat table or plate, face upward, and surrounded by the tube, as shown in partial section in the cut, [page 114]. The tube is a strip of sheet iron, which is bent around the flange and is secured in place by a wire twisted around it. The melted alloy (type, metal and lead) is poured into the space thus formed until it rises a quarter of an inch above the face of the model. In a few minutes it sets and is removed and allowed to cool. This gives a cup with the inscription and design depressed or in intaglio upon its inside base. This is shown in the cut, [page 115], partly in section; it will of course be understood that the mould forms a complete cup.
To make the stamp the interior surface of the mould is oiled with a stiff brush. It is not material what oil is used. The composition melted by heat is then poured into the cup, and is allowed to solidify. Owing to the conical shape of the mould it is readily removed. The mould must be hot but not too much so.
In the Post Office stamps the date requires to be changed frequently. Some of the figures do duty for two or three days each month. Thus the figure 8 is in the designation of three days, the eighth, eighteenth, and twenty-eighth. There are three changes involved therefore in connection with this day numeral. When a stamp mould or matrix is cast the place of numerals that are to be changed is filled with a blank space in the part where the type would otherwise come. A number is stamped in this space when needed, by means of an ordinary steel number-punch.
When the number is to be changed the old character is scraped or cut out, leaving a small irregular hollow. A very small piece of soft lead, about one-sixteenth of an inch on each side, is dropped into the hollow. With a flat faced punch it is flattened out, and on it the new number is impressed by a steel punch. This operation is repeated a great many times before the matrix is worn out.
OPEN SHUT
Composition Stamp Handle.
In the cut, [page 115], one number is shown as stamped into the soft lead, and at the other end of the stamp is a blank space ready for a number.
The casting of a stamp is so extremely simple that no attempt is made to use movable type, as in permanent rubber dating stamps.
While it is obvious that these composition stamps could be attached directly to wooden handles, a special style of handle, shown in the cuts, is employed by the Post Office. A wooden handle carries at its end a brass base, to which is pivotted a swinging piece that is perforated by a conical oval aperture a little larger than the small end of the stamp. The edges of this aperture are slightly rounded.
It is swung around as shown in the first figure, and the stamp, previously moistened on its sides, is forced in. If the stamp is properly made it is surprising how much force may be used to insert it. If the edges of the brass swinging piece are not rounded there is danger of the composition being cut. The stamp in its brass frame is then swung back over the brass base, where it is secured by a catch. The stamp is now ready for use, as shown in the second figure of the [cut].
It is imperative that no aqueous or glycerine ink be employed for continuous work with such stamps. Common printers’ ink is perfectly satisfactory, and the work may be nearly or quite as good as that executed by an india rubber stamp.
The Post Office manufactures a pad for use with printers’ ink into whose manufacture the same composition enters. The ink retainer is a piece of fine felt, one-quarter to one-half an inch thick. This is placed in the bottom of a shallow steel mould, where it enters for half its depth into a recess that it accurately fits. The composition from old stamps, melted up, is then poured upon and around it, the mould being previously oiled. When it is full a piece of strong manilla paper, of the area of the felt only, is placed upon the bottom of the glue pad on its centre, which as it lies in the mould is its uppermost part. The paper adheres strongly as the glue hardens. Eventually it is turned out of the mould, and a pad, shown in the [cut], is produced. The dotted lines show the limits of the felt pad. The glue composition underlies, surrounds and extends outwards from the felt portion. It is found that the elasticity of the composition makes the pad much pleasanter for rapid stamping.
Composition Ink Pad.
The above description gives the clew to making any stamp of this description. The matrix may be of dental plaster, or of oxychloride of zinc cement. The mould may be built up of type of any kind.
The composition is so cheap that the stamp can be made quite thick. This gives it a high degree of elasticity and adaptability to uneven surfaces. It may be mounted by adherence upon a flat board or block, provided, if necessary, with handles. If the board or block is placed upon the composition while it is still warm and liquid, as it solidifies the board and composition will adhere with great tenacity.
All moulds or surfaces to which it is desired that the melted composition shall not adhere must be oiled.
The moulds must not be cold or the composition will not enter the fine divisions. If on the other hand they are too hot the mixture will adhere. Experience will teach the right conditions for success.
Below are given other formulæ for roller composition. The formula already given in this chapter is that used by the United States Post Office Department.
I. “Old Home Receipt:” Glue 2 lbs., soaked over night, to New Orleans molasses 1 gallon. Not durable, but excellent while it lasts.
II. Glue 10½ lbs., molasses 2½ gal., Venice turpentine 2 oz., glycerine 12 oz.; mix as directed above.
CHAPTER XV.
THE HEKTOGRAPH.
For obtaining multiple copies of writing, the apparatus called the Hektograph or Papyrograph has been extensively adopted. In general terms it consists of a tray filled with a jelly like composition. Any imprint made upon the surface with aniline ink can be transferred to paper by simple pressure. The tray filled with composition is called the tablet. It is thus prepared.
The tray may be made of tin or even of pasteboard or paper, and should be about one half an inch deep. It may be of any size, according to the work it is to do. The composition is made from the best gelatine and glycerine. One ounce by weight of gelatine is soaked over night in cold water, and in the morning the water is poured off, leaving the swelled gelatine. Six and one-half fluid ounces of glycerine are now heated to about 200 F. (93 C.) on a water bath preferably, and the gelatine is added thereto. The heating is continued for several hours. This operates to expel the water and to give a clear glycerine solution of gelatine.
The composition is then poured into the tray, which must be perfectly level in order to obtain a surface nearly even with the edge. It is then covered so as to keep off the dust. The cover of course must not come in contact with the smooth surface. In six hours it will be ready for use.
The original copy that is to be reproduced is made upon ordinary paper in aniline ink. One formula for the ink reads as follows: Aniline violet or blue (2 R B or 3 B) 1 oz., hot water 7 fluid oz.; dissolve. After cooling add alcohol 1 fluid oz. and glycerine ¼ fluid oz., a few drops of ether and a drop of carbolic acid. Keep in a corked bottle. Other formulæ are given in chapter XVII.
The writing is executed with an ordinary steel pen. The lines should be rather heavy so as to show a greenish color by reflected light.
The surface of the pad is slightly moistened with a wet sponge and is allowed to become nearly dry. The paper is then laid upon it and smoothed down. This is best done by placing a second sheet over it and rubbing this with the hand. No air bubbles must remain between the copy and the tablet, and the paper must not be shifted.
It is allowed to remain for a minute or less and is then raised by one corner and stripped from the gelatine surface. It will have left the reversed copy of its inscription perfectly reproduced upon the tablet.
At once a piece of ordinary writing paper of the desired size and quality is laid upon the tablet, smoothed down, and stripped off, when it will be found to have taken with it a complete copy of the inscription or writing. This is repeated over and over again with another sheet of paper, until the ink on the pad is exhausted. Fifty or more good copies can be thus obtained.
The Hektograph.
As soon as the work is completed the remains of the ink should be washed off with a moist sponge and the tablet, after drying a little, will be ready for a second operation.
Some practice is required to ascertain the proper strength of the writing and degree of wetness of the surface. When the gelatine surface becomes impaired it can be remelted in a water bath if it is not too dark from absorption of ink.
French Ministry of Public Work Formula.—Glue 100 parts, glycerine 500 parts, finally powdered kaolin or barium sulphate 25 parts, water 375 parts. Use a little hydrochloric acid in the water for washing off the pad after use.
Hektograph Sheets.—Four parts of glue are soaked in five parts of water and three parts of ammonia until soft. It is then heated and there is added to it three parts of sugar and eight parts of glycerine. The mixture is applied to blotting paper. This is saturated with it, and successive coats added until a smooth surface is produced on one side. This is the side for reproduction. It is used like the regular tablet except that it is claimed that sponging off the writing is not necessary. Owing to the capillary action developed by the blotting paper it is supposed to be self-cleaning by standing.
CHAPTER XVI.
CEMENTS.
Before cementing vulcanized rubber the surface should be roughened or still better it may be seared with a red hot iron. For bicycle tyres this is especially to be recommended.
Cement for Cuts in Bicycle Tyres, Rubber Belts, etc.—Carbon bisulphide, 5 ounces; gutta-percha, 5 ounces; caoutchouc, 10 ounces; fish glue, 2½ ounces. After it is applied and has dried the excess can be removed with a wet knife. Bad cuts should first be stitched up.
Bicycle Tyre Cement to fasten Tyres to Rims.—Equal parts of pitch and gutta-percha are melted together. Sometimes two parts of pitch are prescribed. This cement has extended application.
Cement for Paper Boats and for Mending Rubber Goods.—Fuse together equal parts of pitch and gutta-percha, and to this add about 2 parts of linseed oil containing 5 parts of litharge. Continue the heat until the ingredients are uniformly commingled. Apply warm.
Waterproof Cement.—Shellac, 4 oz; borax, 1 oz; boil in a little water until dissolved, and concentrate by heat to a paste.
Another.—10 parts of carbon disulphide and one part of oil of turpentine are mixed, and as much gutta-percha is added as will readily dissolve.
Cement for Mending Hard Rubber.—Fuse together equal parts of gutta-percha and genuine asphaltum; apply hot to the joint, closing the latter immediately with pressure.
Glue to Fasten Leather, etc., to Metals.—1 part crushed nut galls digested 6 hours with 8 parts distilled water and strained. Glue is macerated in its own weight of water for 24 hours, and then dissolved. The warm infusion of nutgalls is spread on the leather; the glue solution upon the roughened surface of the warm metal; the moist leather is then pressed upon it and dried.
Marine Glue, Various Formulæ.—I. Dissolve 1 part of india rubber in 12 parts of benzole, and to the solution add 20 parts of powdered shellac, heating the mixture cautiously over a fire. There is great danger of conflagration. Apply with a brush.
II. Caoutchouc, 1 oz; genuine asphaltum, 2 oz; benzole or naptha, q. s. The caoutchouc is first dissolved (as described in chapter XII.), and the asphaltum is gradually added. The solution should have about the consistency of molasses.
Cement for Vulcanized India Rubber.—Stockholm pitch, 3 parts; American resin, 3 parts; unmixed india rubber, 6 parts; oil of turpentine, 12 parts. Heat and mix very thoroughly. More oil of turpentine may be added as required.
Gutta-Percha Cement for Leather.—Soak gutta-percha in boiling water. Soften in benzole after cutting up for a day. Heat on a water bath until the greater part of the benzole is expelled. When cool it will solidify. Use by heating.
Cement for Rubber Shoes.—
| (1) | Chloroform | 280 | parts. |
| India rubber (masticated) | 10 | ” | |
| (2) | India rubber | 10 | ” |
| Resin | 4 | ” | |
| Venice turpentine | 2 | ” | |
| Oil of turpentine | 40 | ” |
For first solution dissolve by mastication. For second, melt the finely divided gum with the resin, add the Venice turpentine and finally the oil of turpentine. Use heat if necessary. Mix both solutions finally. To apply, saturate a piece of linen with the cement and apply to the spot previously coated with the cement. As it dries apply a little more as required. A finishing varnish is given in the last chapter. Parkes’ cold curing process may be applied as described in chapter XI.
Chatterton’s Compound for uniting sheets of gutta-percha in cable cores and for general work with gutta-percha coated wires.—Stockholm tar, 1 part; resin, 1 part; gutta-percha, 2 parts.
Waterproofing for Wooden Battery Cells.—Resin, 4 parts; gutta-percha, 1 part; boiled oil, a little.
Another Formula.—Burgundy pitch, 150 parts; old gutta-percha in fine shreds, 25 parts; ground pumice stone, 75 parts. Melt the gutta-percha and mix with the pumice stone and then add the pitch, melting all together. Apply melted and smooth off with a hot iron.
Cement for Celluloid.—Shellac, 1 part is dissolved in spirits of camphor 1 part, with 3 to 4 parts strong alcohol. It is applied warm and the parts united must not be disturbed until the cement is hard.
CHAPTER XVII.
INKS.
RUBBER STAMP INK.
| Aniline blue soluble, 1 B | 3 | parts. |
| Distilled water | 10 | ” |
| Acetic acid | 10 | ” |
| Alcohol | 10 | ” |
| Glycerine | 70 | ” |
For other colors the following aniline colors may be substituted in proportions given:
| Methyl violet, 3 B (violet) | 3 | parts. |
| Diamond fuchsin I, (red) | 2 | ” |
| Methyl green yellowish | 4 | ” |
| Vesuvin, B (brown) | 5 | ” |
| Nigrosin, W (blue black) | 4 | ” |
For very bright red 3 parts of Eosin BBN. are used. In this case the acetic acid must be omitted. In all cases the colors should first be rubbed up with the water in a mortar, and the glycerine should be added gradually. These inks will answer for the hektograph.
Hektograph Ink.—Aniline color, 1 part; water, 7 parts; glycerine, 1 part. A little alcohol may be used with advantage to dissolve the aniline color. It can be expelled by heating if it proves objectionable.
Aniline Ink Vehicle.—Prof. E. B. Shuttleworth, of Toronto, Ont., suggests the use of castor oil in place of vaseline and other vehicles for typewriter ink. The aniline colors may first be dissolved in alcohol, and the solution may be added to the oil. They may also be dissolved directly in the oil in which most of them are soluble.
Indelible Stamping Inks.—I. Asphaltum, 1 part; oil of turpentine, 4 parts; dissolve and temper with printer’s ink. The ink may be omitted, and solid dry color added.
II. Sodium carbonate, 22 parts; glycerine, 85 parts; dissolve and rub up in a mortar with gum arabic, 20 parts. In a separate vessel dissolve silver nitrate, 11 parts; in officinal aqua ammonia, 20 parts. Mix the two solutions, and heat to the boiling point, 212° F. (100° C.). After it darkens, add Venice turpentine, 10 parts. After applying to the cloth, a hot iron should be applied, or it should be exposed to the sun.
III. Dr. W. Reissig’s formula:
| Boiled linseed oil varnish | 16 | parts. |
| Finest lamp black | 6 | ” |
| Ferric chloride (sesquichloride of iron) | 2 to 5 | ” |
Dilute a little for use with varnish. After this ink has been removed, no matter how completely it can be detected by dipping the paper into a solution of ammonium sulphide.
IV.
| Aniline black in crystals | 1 | part. |
| Alcohol | 30 | ” |
| Glycerine | 30 | ” |
Dissolve in the alcohol, and add the glycerine afterwards.
Show Card Ink.—
| Pure asphaltum | 16 | parts. |
| Venice turpentine | 18 | ” |
| Lamp-black | 4 | ” |
| Oil of turpentine | 64 | ” |
Dissolve the asphaltum in the turpentine, and thoroughly mix.
Stencil Ink.—Shellac, 2 ounces; borax, 2 ounces; water, 25 ounces. Dissolve by heat if necessary, first the borax alone, and then adding the shellac. To the clear solution add gum arabic, 2 ounces. Color with lamp-black, with Venetian red, or with ultramarine, to suit the taste. Another formula gives shellac, 4 parts, borax, 1 part, and omits the gum arabic.
Copying Ink (for use without a press by simply pressing and rubbing with the hand), by Prof. Attfield, F.R.S.—Use ink of any kind of extra strength. This in many cases can be made by evaporating common ink down to six tenths of its volume. Then mix with it two thirds of its volume of glycerine, so as to restore the original volume.
White Ink.—Barium sulphate, or “flake white” is mixed with gum arabic water of sufficient thickness to keep it suspended, at least while in use. Starch or magnesium carbonate or other white powder may be used instead of the barium sulphate. The powder must be of impalpable fineness.
White Ink on Blue Paper.—A solution of oxalic acid in water is used for this purpose. It may be applied with a rubber stamp or with a common pen. A quill or gold pen is the best as a steel pen is soon corroded. The ink bleaches the paper wherever it touches it, giving white lines on a blue ground.
Gold Ink.—Gold leaf with honey is ground up in a mortar, best an agate mortar, or on a painters’ slab with a muller. It is added to water, and thoroughly mixed and at once poured off from the first sediments, filtered out, and washed. This is done to secure the impalpably finely ground gold only. The resulting powder is mixed with a suitable vehicle, such as white varnish or gum arabic water.
Silver Ink.—As above, using silver leaf.
Zinc Label Ink.—I. Verdigris, 1 part; ammonium chloride, 1 part; lamp-black, ½ part; water, 10 parts.
II. Platinum bichloride, 1 part; gum arabic, 1 part; water, 10 parts.
Diamond Ink for Etching Glass.—This consists essentially of hydrofluoric acid mixed with barium sulphate to the consistency of cream. The barium sulphate is quite inoperative except as giving a body to prevent the ink from spreading. It is applied with a rubber stamp or pen and allowed to remain for ten minutes or until dry. On removal of the white powder, the design will be found etched on the glass. The following is a formula for it.
Saturate hydrofluoric acid with ammonia, add an equal volume of hydrofluoric acid and thicken with barium sulphate in fine powder.
CHAPTER XVIII.
MISCELLANEOUS.
To Soften and Restore India Rubber Hose, etc.—I. Dip in petroleum and hang up for a couple of days. Repeat process if necessary.
II. The above process is applicable to all articles, but is specified for hose. It is stated that old rubber that has become hard may be softened by exposure first to vapor of carbon disulphide, followed by exposure to the vapor of kerosene. The latter vapor is found to be a general preservative for india rubber.
III. Dr. Pol recommends immersion in a solution of water of ammonia, 1 part, and water 2 parts, from a few minutes to an hour.
To Prevent Decay of Rubber Tubing.—The decay of rubber tubing has been attributed to the formation of sulphuric acid from the sulphur mixed with it. M. Ballard has suggested washing with water or weak alkaline solution five or six times in a year.
Joints between India Rubber Tubing and Metal.—Where tubing is temporarily slipped over metal gas pipes and similar connections, as in the chemical laboratory, it is well to apply glycerine to the metal. It acts as a lubricant in slipping the tubing on, and assists in its withdrawal.
Preserving Vulcanite.—Wash occasionally with a solution of ammonia and rub with a rag slightly moistened with kerosene oil.
Effect of Copper upon Rubber.—In a paper read before the recent meeting of the British Association, Sir William Thomson stated that metallic copper, when heated to the temperature of boiling water, in contact with the rubber, exerted a destructive effect upon it. With a view to finding whether this was due to the copper per se, or to its power of conducting heat more rapidly to the rubber, he laid a sheet of rubber on a plate of glass, and on it placed four clean disks, one of copper, one of platinum, one of zinc and one of silver. After a few days in an incubator at 150° F., the rubber under the copper had become quite hard, that under the platinum had become slightly affected and hardened at different parts, while the rubber under the silver and under the zinc was quite hard and elastic. This would warrant the inference that the metallic copper had exerted a great oxidizing effect on the rubber, the platinum had exerted a slight effect, while the zinc and silver respectively had no injurious influence on it. The rubber thus hardened by the copper contained, strange enough, no appreciable trace of copper; the copper, therefore, presumably sets up the oxidizing action in the rubber without itself permeating it.
Gas Tight Tubings.—Fletcher has invented a gas tight rubber tubing in which a layer of tinfoil is interposed between two concentric rubber tubes, all vulcanized together.
Printing Colors upon India Rubber.—It may sometimes be desirable to have a surface of vulcanized india rubber so prepared that it will take colors such as are used for calico printing. This end is simply attained by sprinkling the article with farina before vulcanizing. A small quantity attaches itself and forms an excellent base for color printing.
Gutta-Percha for Coating Glass.—For focusing glass in photography and for similar purposes where ground glass or a translucent material is required, a solution of gutta-percha in chloroform is highly recommended. This is flowed over or painted on the glass and is allowed to evaporate afterwards.
Burned Rubber.—A very soft pure gum sold for artists’ use is improperly termed burned rubber. It is used in crayon work for removing and lightening marks by dabbing it against the paper, cleaning the rubber from time to time. It is so soft that it picks up and removes crayon marks without the necessity of friction. Thus the rubbing out or more properly erasing operation can be localized and crayon tints can be lightened in tone without impairment or “smutting.” It is a very elegant accessory to the artists’ paraphernalia. To make it, pure virgin gum, preferably the best Para, is cut into pieces and soaked for some hours in benzole. A long soaking is advisable. The pieces are then removed from the benzole and are ground in a mortar until perfectly homogeneous. The mass is gathered up with a spatula and is pressed into little tin boxes. If desired it may be dried upon a water bath. This is not necessary as, if the box is left open, it will rapidly season itself. It should be very soft, should tend to adhere to the fingers, yet should leave them easily, and should strip cleanly from the box. A very little turpentine makes it more adhesive. It may even be softened in turpentine alone. This gives a gum that seasons more slowly and is in some respects preferable to the benzole made preparation. It is sold at a high price by the dealers, as the demand for it is limited.
Rubber Sponge.—This is also an artist’s rubber. It is also used for cleaning kid gloves. It is made by incorporating with the masticated or washed and sheeted gum any material or materials that will give off vapor in the curing process. Damp sawdust and crystallized alum are used as giving off vapor of water or steam, or ammonium carbonate as giving off vapors of ammonia carbonic acid gas and steam. The mixed gum may be cured in moulds, which it will fill by its expansion.
Shellac Varnish for India Rubber.—This is made by soaking powdered shellac in ten times its weight of strong aqua ammonia (26° B.). At first no change beyond a coloring of the solution is perceptible. After many days standing the bottle, which should have a glass stopper, being tightly closed, the shellac disappears, having entered into solution. It may be a month before complete solution. This forms an excellent varnish for india rubber shoes and similar articles. It may be applied with a rag. It is also a good application for leather in some cases and doubtless many other uses could be made of it. It would act well as a vehicle for a dark pigment such as lamp-black. It will rejuvenate a pair of india rubbers very nicely. The ammonia exercises also a good influence on the rubber. It has been recommended as a cement for attaching rubber to metal, but its adhesive powers are not always satisfactory.
Simple Substitute for Stamps.—A very simple though rough and imperfect substitute may be made by gluing with common carpenter’s glue pieces of thick string upon a piece of wood, the string being given the form of the desired letters. Care must be taken to avoid saturating and stiffening the string with the glue.
India Rubber Substitutes.—One of these under the name of vulcanized oil is thus described by Bolas:
“Vulcanized oil is, perhaps, of more interest, and many oils, such as linseed and others resembling it, may be vulcanized by being heated for some time to 150° Centigrade with twelve to twenty per cent. of sulphur. The product obtained is soft, and somewhat resembles very bad india rubber. By increasing the proportion of sulphur very much indeed, say to four times the weight of the oil, and vulcanizing at a higher temperature, a hard substance, resembling inferior vulcanite, is obtained.
“Soft and hard vulcanized oil have been introduced into commerce at various times and under many names; but these materials never seem to have made very much headway.”
Another method of treating the oil consists in mixing it with a solution of chloride of sulphur in carbon disulphide or in naptha. On standing, the volatile solvents escape, leaving a thick mass, which is the substitute.
In combinations of aluminum with the fatty acids, forming aluminum soaps, and of these, aluminum palmitate especially, a substitute for india rubber has been sought but without success.
Metallized Caoutchouc.—Unvulcanized gum is mixed with powdered lead, zinc, or antimony. The mixed india rubber is then cured as in the regular process.