The extract of lead is a well-known commercial article, and it is well suited for this purpose; but the inventor does not limit himself to this particular preparation, as there are a larger number of neutral and basic compounds of lead that may be so modified as to produce results similar, if not identical, with the results obtained by the formula above given. Gelatine may be treated instead of glue.
Compositions for printing rollers. All such compositions contain gelatine or glue. The following receipts are used:
| I. | II. | III. | IV. | V. | VI. | VII. | VIII. | |
| Glue | 8 | 10 | 4 | 2 | 32 | 2 | 1 | 3 |
| Molasses | 12 | — | 8 | 1 | 12 | 6 | 2 | 8 |
| Paris white | 1 | — | — | — | — | — | — | 1 |
| Sugar | — | 10 | — | — | — | — | — | — |
| Glycerin | — | 12 | — | — | 56 | — | — | — |
| Isinglass | — | 1½ ozs. | — | — | — | — | — | — |
| India rubber in naphtha | — | — | — | — | 10 | — | — | — |
A patent roller composition is thus made: Gelatine 32 lbs. and glue 4 lbs. are softened in cold water and melted in a glue boiler. To this are added 4 lbs. of glucose, 72 lbs. of glycerine, and 1 oz. of methylated spirit. The whole is then digested for four to six hours and cast into rollers. This composition is claimed to be unaffected by temperature, to retain its elasticity, and not to shrink.
In practice it is found that all these compositions from the cleansing and remelting become gradually sticky and useless. To partially overcome this difficulty, formaldehyde is added to the roller composition, which renders the glue insoluble in water, and thus prolongs the life of the roller.
Size. This product is simply an undried glue and is used, not for adhesiveness, but as a body for filling porous surfaces, such as wood or plaster, stiffening and weighting textile fabrics, in paper manufacture, and as a foundation for oil paints and varnishes. According to Thomas Lambert, many firms who have a good selling connection for size, do not go to the expense of erecting clarifying plant and drying house for treating the glue-liquors, but prefer to stop the process half way, as it were, and marketing the resulting product as size. Others, again, with a complete glue plant at hand, convert only a portion of their liquors into size, to meet trade demands, the bulk going for the manufacture of glue. Size varies in quality to suit the requirements of different trades. Cardboard box-makers prefer a strong skin size, which is manufactured red or yellow as preferred. A strong yellow size made from bone is used by calico-printers, paper-stainers, wall-paper manufacturers, and in the straw-hat and carpet trades.
In the preparation of skin-glue, the first and second liquors are used for that purpose; the residual mass is then treated with water and steam, which practically exhausts the gelatinous matter. This, the third liquor, is used solely for size. During the boiling, samples are taken at intervals, cooled, and the condition of the jelly noted. The strength is also taken by the glue meter, which registers the percentage. At a strength of 8 to 10 per cent. the liquor is run off, passing through a filter of fine shavings or cloth, to remove any suspended matter, into a wooden vat fitted with a steam coil, then heated with a moderate charge of sulphurous acid to bring up the color, and evaporated to a strength of 36 to 38 per cent., as may be desired, and then run into casks to jelly. If skin-glue is not made, the three runnings are used entirely for size.
An outline of a simple process used in an English factory devoted to making tub-size, as given by Samuel Rideal, may be interesting.
The material is obtained from the tanyard ready limed and freed from hair, and consists mainly of “faces” of bullocks or cows, the noses being cut off as food for dogs. It is soaked again in weak lime water and re-washed, then placed in coppers made of wrought-iron wielded in one piece, and holding about 10 to 20 gallons, enclosed in outer jackets of the same material containing water which is kept well boiling. There are six coppers, about five feet high by three feet in diameter. The charge of each is about ½ cwt. The material is covered with water and well stirred with sticks for two hours, the scum and dross being occasionally skimmed off and thrown away as useless. At the end the size is ladled on to sieves, from which it runs into cooling vats, and is filled while moderately hot into clean tubs.
The liquor is clear and of a light brown color for the best XX quality, and darker for the common. The coolers or setting-backs are of wood or zinc, and the liquid is not kept hot longer than it can be helped, as it is liable to turn sour.