Muzmann and Krakowitzer dissolve 10 lbs. of gelatine and 10 lbs. of tallow soap in 30 gallons of boiling water, and mix the solution in 4 gallons of water in which 15 lbs. of alum have been dissolved. The whole is boiled for half an hour, and then allowed to cool to 104° F. At that temperature the fabric is thoroughly soaked in it, dried, rinsed, again dried, and finally calendered. In this process the alum partially decomposes the soap, forming either free fatty acid or an acid alumina soap. The gelatine forms an insoluble compound with the alum. The free fatty acid or acid soap is mostly carried down on the fibre by the precipitate formed by the alum and the gelatine.
Glue for Joints in Leather Driving Belts.—Soak equal parts of good hide glue and isinglass in water for 10 hours, and then boil with pure tannin till the product becomes sticky. The surfaces to be cemented together should be roughened and the glue applied hot.
According to another method 2 lbs. of best glue are dissolved at a moderate heat in 3 lbs. of water and about 3 drachms of carbolic acid stirred into the hot solution. The mixture is poured into shallow iron pans to congeal, when it is cut in pieces and dried in the air. For use the glue is liquefied by adding a small quantity of vinegar and applied with a brush to the leather. The joint is finally pressed between iron plates at a temperature of about 77° F.
Hectograph Mass.—Soak a good quality of glue for 24 hours in sufficient cold water to cover it. Then take the swelled glue from the water and melt it in an enameled pot over a moderate fire. When perfectly liquid add the required quantity of glycerine (see formulas below) and intimately mix both by continued stirring.
The vessel containing the mixture should for some time be kept hot, so that the mass remains thinly fluid. The purpose of this is to allow the air-bubbles formed by stirring to rise to the surface. If any scum is formed on the surface, remove it carefully with a shallow spoon. The composition is then ready to be poured into the vessel intended for its reception, which may be made especially for the purpose, or a shallow baking pan of tin may be used. When the pan is filled with the composition place it perfectly level in a cool place free from dust and allow to remain at least for several hours.
Formulas for Hectograph Masses.—I. Gilder’s glue, 100 parts; glycerine of 28° Bé., 500.
The glue is allowed to swell in water, as described above, then melted, mixed with the glycerine, and evaporated to the required consistency.
II. Gilder’s glue, 100 parts; glycerine of 28° Bé., 400; water, 200.