ELEMENTARY PHYSIOLOGICAL CHEMISTRY 177 



(b) Albuminates. These are compounds of native proteids with 

 mineral salts, acids, alkalies, or the halogen elements. 



EXPERIMENT XIV. To a few c.c. of diluted egg-white add a few 

 drops of mercuric chloride solution ; a white coagulum of albuminate of 

 mercury is formed. 



EXPERIMENT XV. To some diluted egg-white add two or ^hree 

 drops of 10 % HC1. Place this on the water-bath at body -temperature 

 for five minutes. Divide into two parts a and b. Boil the portion a 

 no coagulum appears because the native proteid has been changed into 

 acid albumin or ' syntonin ' which does not coagulate on boiling. 



To the portion b add sufficient litmus solution to stain it red, and 

 then, drop by drop add 1 % solution of Na 2 C0 3 till the solution is 

 neutral; a precipitate of acid albumin comes down. Add a slight 

 excess of the alkaline solution, and the precipitate redissolves. Acid 

 albumin is insoluble in neutral saline solution, but soluble in weak 

 acids and alkalies. It is also insoluble in distilled water. 



Alkali albumin can be produced by using weak caustic potash 

 instead of the acid in the above experiment. It gives the same 

 reactions as acid albumin, but differs in containing less sulphur 

 and nitrogen, for, as has been explained on p. 169, treatment with 

 alkali separates the loosely combined portions of these elements from 

 proteid. Acid albumin can, therefore, be changed into alkali albumin, 

 but the reverse change of alkali into acid albumin is impossible. 

 Both albuminates can be precipitated in weak acid or alkaline solution 

 by neutral salts. They, therefore, behave like globulins (see below) in 

 this respect, but differ from them in that they cannot be coagulated by 

 heat. If, however, the neutralisation precipitate l of either albuminate 

 be heated it changes into a coagulum insoluble in its original solvents. 



Acid albumin, when prepared from myosin, is called Syntonin, 

 and alkali albumin, when prepared by the action of strong caustic 

 alkali on proteid, is called ' Lieberktthn's jelly.' Acid albumin is 

 the first product of peptic digestion of proteids, as alkali albumin is 

 the first stage of pancreatic digestion. 



(c) Proteoses and Peptones. These are produced from native pro- 

 teids by hydrolysis, either by means of mineral acids or superheated 

 steam, or through certain ferments such as exist in the digestive juices 

 secreted respectively by the stomach and pancreas. They will be 

 studied under " Digestion." 



(d) Coagulated Proteids. As explained above, coagulation of pro- 

 teids may be produced by various agencies, of which ferment action 



1 " Neutralisation precipitate " means the precipitate produced by neutralising 

 a solution containing either albuminate. 



M 



