418 ORGANIC CHEMISTY. 



Wliat isgela- 1040. GELATINE. Gelatine is soluble in 

 tine? water, and yields a stiff jelly on cooling 



from a hot solution. On this property is based its use 

 in the preparation of jellies for the table. The com- 

 mercial article employed for this purpose and ordinary 

 glue are essentially the same. 



1041. The substance known as isin- 



Crive the com- 7 ., -I--I--II-IT < 



position and glass, is the dried air bladder of a species 

 ^ stur o eon 5 au & forms m its natural con- 

 dition, a soluble gelatine. Gelatine contains 

 the four principal organic elements ; nitrogen and oxy- 

 gen being in somewhat larger proportion than in the 

 protein bodies. Hoofs, hair, and the other substances 

 above mentioned, contain sulphur in addition. Gelatine 

 is susceptible, like the protein bodies, of putrefaction, 

 and also of exciting fermentation. As starch is changed 

 into sugar by the action of dilute sulphuric acid, so by 

 the action of oil of vitriol, gelatine may be converted 

 into a sweet crystalline substance, called glycocoll or 

 sugar of gelatine. 



1042. HIDES, TANNING. A solution of 



What chemical 



combination gelatin forms, with tannin or tanmc acid, 



tan ~ a tenacious insoluble precipitate. The 

 tanning of leather depends on the forma- 

 tion of this insoluble compound in the hides which 

 are submitted to the process. They are im- 

 mersed for this purpose in an infusion of oak 

 and hemlock bark, until the combination has 

 taken place throughout the whole thickness. 

 They are thus secured against putrefaction 

 and converted into firm, elastic leather. Hides may 



