133 
THE MANUFACTURE OF GLUE. 
Ordinary glue is made by boiling the scrapings and clippings of hides, 
hoofs, horns, or the feet of horses, cows, sheep, and pigs, which has the 
effect of converting a certain substance, known to chemists as osseine, 
and existing in those parts of the animal, into gelatine or glue. 
The raw material is first placed in large pits or tanks, containing 
milk of lime. The lime, being a strong alkali, removes the hair from 
the skin in the course of a few days, the time varying with the heat of 
the weather and the age of the stuff. When all the hair is removed, 
the skins are taken out of the lime-pits, and washed with large 
quantities of water to free them from the lime, which would act upon 
the skin in the same way it acted on the hair. When sufficiently 
washed, they are placed under a powerful hydraulic press, and as much 
of the water as possible squeezed out of them. Sometimes, instead of 
being washed after their immersion in the lime-bath, they are simply 
spread upon frames in the open air to dry. The action of the atmo- 
sphere soon converts the lime into common chalk, which being perfectly 
neutral, has no further corrosive action on the skin. Manufacturers 
appear to be divided as to which of these methods of preparation is the 
better one. 
The whole of the hair and most of the fat being removed from the 
skins, they are next thrown into a huge wrought-iron boiler full of 
water, which has a_ false bottom provided with a light framework of 
iron, to prevent the smaller pieces from sticking to the bottom and sides. 
Some manufacturers put the skins into a large network bag, made of 
rope, which is wound in and out of the boiler by a windlass, — but 
generally, they are thrown in without this accessory. 
The hair and waste pieees of the skin and fat left in the lime-pits 
are collected into heaps, allowed to rot, and then sold to the manure 
manufacturers. 
The boiling gradually converts the osseine, which, as we have before 
stated, exists in the skins already formed, into gelatine, which dissolves 
in the water. The solution of gelatine thus made is, when sufficiently 
strong, run off into a settling vat, where, while still being kept warm, the 
mechanical impurities gradually fall to the bottom. When pretty 
clear, the solution is run off into a long trough, which communicates 
with a number of smaller ones, six feet long by two feet deep and one 
foot broad. As it runs into the trough a little alum is added, which 
appears to have the effect of clarifying the solution still further. As 
the solution cools in the trough, it forms a firm mass of the consistency 
of calf s foot jelly. The troughs are then carried into the cutting-up 
shed, where a man runs a knife round the sides to separate the glue from 
the wood, and afterwards divides it into " bricks, 1 ' two feet deep by one 
foot long, and about eight or nine inches wide. These " bricks " 
are then taken out, and cut with a wire or a sharp knife into slabs about 
