438 



SMITH'S INTERMEDIATE CHEMISTRY 



When bones or dried blood are subjected to destructive dis- 

 tillation (compare p. 420), the residue consists of animal charcoal. 

 The charcoal from bones (bone black) contains 90 per cent of 

 mineral matter, largely calcium phosphate, and only 10 per cent 

 of carbon. Animal charcoal, being a very active adsorbent 

 (p. 421), is used in sugar refining. 



The basis of wool, and of hair fibers in general, is a protein 

 called keratin. The silk fiber is also of animal origin, but differs 

 very widely from wool in its structure and properties. As spun 

 by the silkworm in the preparation of its cocoon, it consists of 

 two filaments composed of a protein called fibroin surrounded and 

 cemented together by a gluey substance known as sericin or silk- 

 gum. 



Glue, an impure form of gelatine (p. 435), is obtained from the 

 skin and bones of animals by extraction with water under pressure. 

 Leather is prepared from the hides by tanning (see p. 533). 



Casein, a protein contained in milk and precipitated therefrom 

 by dilute acids, has recently found many interesting applications. 

 In the modified form of cheese, of course, it has long been of value 

 as a food. Mixed with various alkalies it gives glues, cements 

 and putties. It is used as an ingredient in paints, and for sizing 

 or enameling paper. Paper bottles are made waterproof by im- 

 pregnating them with casein and then exposing them to the vapor 

 of formaldehyde (p. 348). Galalith (milk-stone) is a plastic, 

 harder than celluloid (p. 480) and non-inflammable, made by 

 the same hardening action of formaldehyde on casein. 



Soap. When fats are hydrolyzed by heating with a solution 

 of caustic soda NaOH, instead of water, the sodium salts of the 

 acids are obtained. These sodium salts are known as soaps and 

 the operation is called saponification : 



3NaOH 



palmitin 



C 3 H 5 (OH) 3 



glycerine 



3Na(C0 2 Ci 5 H 3 i) 



sodium palmitate 

 (a aoap) 



