ANIMAL AMIDES. 



then strained through baskets to separate the undissolved portions, 

 suffered to settle, and then farther evaporated till, on being pour- 

 ed into flat moulds, it concretes on cooling into solid gelatinous 

 cakes, which are cut in pieces, and dried on a kind of mat. In 

 France and Germany glue is made by boiling bones. Some 

 years ago Mr Yardley of Camberwell took out a patent for ex- 

 tracting glue from triturated bones, and contrived an ingenious 

 apparatus for the purpose. It is commonly believed that glue, 

 from ox hides, is stronger than that from bones. I have never 

 had an opportunity of comparing them together, so as to enable 

 me to judge of the validity of this opinion. 



Glue consists chiefly of gelatin ; mixed, however, with various 

 impurities, which may be removed in the following manner : 

 Put the glue into cold water. It gradually absorbs moisture, 

 and swells into a tremulous jelly, but does not dissolve. Pour 

 off this cold water once in twenty-four hours, and substitute a 

 new portion in its place till the liquid ceases to dissolve any thing 

 from the glue. Let it be now broken in pieces, and suspended 

 in a cloth in a great quantity of water of the temperature of about 

 60. Any thing still soluble will be taken up by the water, and 

 the glue left nearly pure. If we now take this jelly and heat it 

 to 122, it will become liquid, and may be passed through a cloth 

 or a filter, leaving behind it any coagulated albumen and mucus 

 which it may have contained. On cooling it again assumes the 

 form of a jelly, which may be dried in a low heat It is now 

 pure gelatin or collin. 



Collin thus obtained is colourless, transparent, hard, and ex- 

 ceedingly cohesive. It is insipid, and has no smell. When 

 thrown into water it swells very much, and is converted into a 

 tremulous jelly ; but none of it dissolves. This tremulous jelly 

 becomes liquid when heated up to 93, and again assumes the 

 gelatinous form on cooling. 



From the experiments of Dr Bostock, we learn, that when one 

 part of isinglass (which is nearly pure gelatin) is dissolved in 

 1 00 parts of hot water, the solution on cooling is wholly convert- 

 ed into a jelly. But one part of isinglass, in 150 parts of water, 

 does not become concrete ; though the solution is to a certain de- 

 gree gelatinous.* 



* Nicholson's Jour. xi. 250. 

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