GELATIN. 201 



greyish-white, opaque, without lustre, hard, friable, and has a 

 specific gravity of 1*355. And when again moistened with wa- 

 ter, acquires the taste and smell of soap. The action of reagents 

 on it is the same as on casein. 



CHAPTER II. 



OF GELATIN. 



THE term gelatin was introduced into chemistry to denote glue, 

 when deprived by a chemical process of all its impurities. The 

 name was contrived to point out the characteristic property of 

 pure glue. When put into water it swells up into a bulky gela- 

 tinous substance, but does not dissolve. When this jelly is heat- 

 ed up to 93 it dissolves in the water ; but the whole solution 

 assumes the form of a jelly when it is allowed to cool. It has 

 been shown by M. J. Miiller that there are two species of gela- 

 tin, one which is not precipitated from its aqueous solution by 

 the addition of acetic acid, while acetic acid precipitates the whole 

 of the second species. As it is necessary to distinguish these two 

 species from each other, the first, which is obtained by boiling 

 skins and bones in water, is called common gelatin, or we may 

 give it the shorter appellation of collin* The second species, 

 which is obtained by boiling the permanent cartilages, has been 

 called chondrin by Miiller. We shall describe these two species 

 in succession. 



SECTION I. COMMON GELATIN OR COLLIN. 



Glue was well known to the ancients, and is said by Pliny to 

 have been first made by Daedalus, who lived in the time of Solo- 

 mon, or about 1000 years before the commencement of the 

 Christian era. It was applied by the ancients to the same pur- 

 poses for which it is used by the moderns. In this country it is 

 made from the clippings or parings of the skins of oxen, or other 

 large and full-grown animals. They are boiled in fresh water 

 till they are dissolved, and the liquid begins to get thick. It is 



* From *e xx at, glue. 



