4 ANIMAL PROTEINS 



7O-75 C., the gelatins (if swollen) dissolve readily, whilst 

 the keratins only dissolve at temperatures above 100 C. 

 Albumins and keratins may be distinguished also from 

 gelatins by adding acetic acid and potassium ferrocyanide 

 to their aqueous solutions. Albumins and keratins give a 

 precipitate, gelatins do not. Another distinguishing reaction 

 is to boil with alcohol, wash with ether, and heat with h) T dro- 

 chloric acid (S.G. 1*2). Albumins give a violet colour, 

 keratins and gelatins do not. 



Albumins may be first discussed. They are typified 

 by the casein of milk and by white of egg. Their solutions 

 in water are faintly alkaline, optically active, and laevo- 

 rotatory. They are coagulated by heat and also by mineral 

 acids, alcohol, and by many poisons. The temperature of 

 coagulation (usually about 72 C.) is affected by mineral 

 salts, the effect being in lyotrope order (see Part V., Section 

 I.). The coagulated albumin behaves in most respects like 

 a keratin. Some of the albumins (globulins) are, strictly 

 speaking, not soluble in cold water, but readily dissolve in 

 weak solutions of salt. The albumins are coagulated from 

 these solutions, as usual, when heated. Into this special 

 class fall myosin (of the muscles), fibrinogen (of the blood) 

 and vitellin (of egg yolk). By a gentle or limited hydrolysis 

 of the albumins with dilute acids in the cold, a group of 

 compounds called albuminates are obtained. They dissolve 

 in either acids or alkalies, and are precipitated by exact 

 neutralization. They may also be " salted " out by adding 

 sodium chloride or magnesium sulphate. They are not 

 coagulated by heat. After further hydrolysis with either 

 acids, alkalies or ferments, very soluble compounds are 

 obtained called albumin peptones or albumoses. These are 

 soluble in alkalies, acids and water, and are readily hydro- 

 lyzed further into amido acids and acid amides. They are 

 very similar to the peptones obtained from keratins and 

 gelatins. They are not coagulated by heat. 



Keratins are typified by the hair of animals. They 

 soften somewhat in cold water and even more in hot water, 

 but are not dissolved until digested for some time at tern- 



