THE PROTEINS. 25 



been previously removed by allowing them to remain in weak 

 HC1 for several days, serve as excellent material for the 

 preparation of gelatin. 



Place the substance in an evaporating-dish half full of 

 slightly acidulated water and continue to boil until the 

 material is dissolved. Do not allow the solution to become 

 concentrated. Prolonged boiling will also cause the gelatin 

 to be converted into gelatoses which do not possess the 

 power of gelatinization. 



Make the following tests, dissolving the jelly in hot water 

 as it is needed: 



(a) Biuret; (6) Millon's; (c) Acetic acid and potassium 

 ferrocyanide; (d) Tannic acid; (e) HC1 or H 2 S0 4 ; (/) Satu- 

 ration with (NH 4 ) 2 S0 4 ; (g) Lead-blackening sulphur; (h) 

 Adamkiewicz. Note and compare the results carefully with 

 those obtained with proteins. 



KERATINS. 



These form the chief constituent of hair, nails, hoofs, horns, 

 feathers, etc. Their main characteristic is insolubility, and the 

 relatively large percentage of sulphur which they contain. 

 This is probably present in a cystine nucleus in the molecule, 

 and the largest part is given off in the lead-blackening form. 

 Use horn shavings for the following reactions: 

 (a) Lead-blackening sulphur; (6) Millon's; (c) Xantho- 

 proteic; (d) Adamkiewicz; (e) Try its solubility in water, 

 dilute acids, and alkalies. 



