CHEMISTRY OF BONE. 55 



animal or organic part of the bone is then left as a tough, 

 flexible mass, retaining perfectly the shape of the original 

 bone. 



When long boiled in water the greater part of the 

 animal portion of bone is turned into gelatine and dis- 

 solved in the water; most of the gelatine which we buy in 

 the shops is obtained by boiling fresh bones in a closed 

 vessel under a high pressure; the water then gets much 

 hotter than when boiled in the air, and dissolves out the 

 gelatine more quickly; when a shin of beef is used to 

 make soup the bones are put in as well as the softer parts, 

 and the whole is kept boiling for hours so as to get some 

 of the gelatine out of the bones. The animal matter of 

 bone gives it its toughness and flexibility. 



The earthy portion may be obtained free from the 

 animal by calcining a bone in a bright fire. The residue 

 is a white and very brittle mass, which retains perfectly 

 the shape of the original bone. It is readily powdered and 

 then forms bone ash, which consists chiefly of phosphate 

 and carbonate of calcium; most of the phosphorus of 

 commerce is obtained from it. If the burning be imper- 

 fect the animal matter is charred but not altogether burnt 

 away, and a black mass, known as animal charcoal or 

 " bone black/' is left. 



What then remains behind ? What are its properties? Has it still 

 the shape of the bone ? What happens when a bone is boiled for 

 hours? How is the gelatine of commerce obtained? Why do we 

 use bones in making soup ? What properties does its animal matter 

 confer on bones ? 



How may we get the mineral part of bone free from the animal ? 

 What are its properties when isolated ? What is bone ash ? From 

 what is phosphorus prepared ? What is animal charcoal? 



sheep's rib in the mixture for four or five days, having previously scraped the 

 bone quite clean. It will be found so flexible that a knot may be tied on it; the 

 specimen may be preserved in strong brine or dilute alcohol from year to year 

 for exhibition to a class. 



