GELATIN FROM SILK. 217 



12. Bones softened by osteomalacea yield neither collin nor 

 chondrin. When such bones are long boiled in water we obtain 

 an extract which is quite liquid, and does not gelatinize. When 

 filtered it has a brownish yellow colour. It is precipitated by 

 tannin and alcohol, but not by acetic acid, acetate of lead, or per- 

 sulphate of iron. Sulphate of alumina produces very little al- 

 teration on it, only a scarcely perceptible precipitate of flocks 

 redissolved by adding an excess of the reagent. Caustic potash 

 ley occasions no precipitate. These remarks apply to the very 

 highest stage of osteomalacea when the bones are quite flexible 

 and feeble.* 



SECTION III. GELATIN FROM SILK. 



This is probably the substance described by Hoard under the 

 name of yum.} Mulder first obtained it in a state of purity in 

 1836, described its properties, \ and subjected it to a chemical 

 analysis. He obtained it from raw silk in the following man- 

 ner : 



The silk was boiled successively in water till every thing solu- 

 ble in that liquid was taken up. The aqueous solutions were 

 evaporated to dryness, and the residue was treated with alcohol 

 and ether. What remained after the action of these liquids was 

 digested in hot water. The aqueous solution being evaporated 

 to dryness, the residue was considered as pure gelatin from silk. 



It has a yellowish colour, is translucent, brittle, and destitute 

 of taste and smell. It is heavier than water, and is not altered 

 by exposure to the air. When heated in the open air it swells, 

 burns with flame, and leaves a bulky charcoal. When this char- 

 coal is consumed a white ash remains, consisting chiefly of car- 

 bonate of soda. 



It is soluble in water ; but insoluble in alcohol, ether, fat and 

 volatile oils. The aqueous solution is very viscid ; it speedily 

 undergoes decomposition, giving out an ammoniacal odour. In 

 concentrated sulphuric acid it dissolves at the common tempera- 

 ture of the atmosphere without any change of colour. When 

 heat is applied the solution becomes black, and gives out a mixed 

 smell of caromel and sulphurous acid. In dilute sulphuric acid 



* Muller ; Poggendorf's Anrmlen, xxxviii. 322. f Ann. de Chim. Ixv. 60.. 

 t Poggendorfs Annalen, xxxvii. 606. Ibid. xl. 284. 



