96 HOW CEOPS GROW. 



potash and soda-lye ; acids separate them from these solutions, strciig 

 acetic acid dissolves them with one exception. In very dilute mineral 

 acids (sulphuric and chlorhydric) some of them dissolve in great part, 

 others swell up like jelly. 



: Coagulation. A remarkable characteristic of the group 

 of bodies now under notice is their ready conversion from 

 the soluble to the insoluble state. In some cases this 

 coagulation happens spontaneously, in others by elevation 

 of temperature, or by contact with acids, metallic oxides, 

 or various salts. 



The albuminoids, when subjected to heat, melt and burn 

 with a smoky flame and a peculiar odor that of burnt 

 hair or horn, while a shining charcoal remains which is 

 difficult to consume. 



Tests for tlie Albuminoids. The chemist employs the 

 behavior of the albuminoids towards a number of reagents* as tests 

 for their presence. Some of these are so delicate and characteristic as 

 to allow the distinction of this class of substances from all others, even 

 in microscopic observations. 

 / 1. Iodine colors them intensely yellow or bronze. 



2. Warm and strong cJdorJiydric add colors all these bodies blue or 

 Tiolet, or, if applied in large excess, dissolves them to a liquid of these 

 colors. 



3. In contact with nitric acid they are stained a deep and vivid yellow. . 

 Silk and wool, which consist of bodies closely approaching the albumin 

 oids in composition, are commonly dyed or printed yellow by means of 

 nitric acid. 



4. A solution of nitrate of mercury in excess of nitric acid, f tinges ^V 

 them of a deep red color. This test enables us to detect albumin, for \ 

 example, even where it is dissolved in 100,000 parts of water. 



Albumin* Animal Albumin. The white of a hen s 

 egg on drying yields about 12 per cent of albumin in a 

 state of tolerable purity. The fresh white of egg serves 



* Reagents are substances commonly employed for the recognition of 

 bodies, or, generally, to produce chemical changes. All chemical phenomena re- 

 Bult from the mutual action of at least two elements, which thus act and react on 

 each other. Hence the substance that excites chemical changes is termed a re 

 agent, and the phenomena or results of its application are called reactions. 



t This solution, known as Millon s test, is prepared by dissolving mercury 

 in its own weight of nitric acid of ep. gr. 1.4, heating towards the close of th 

 process, ajid finally adding to the liquid twice its bulk of water. 



