A VISIT TO A BONE BOILING FACTORY. 141 



most solid kind, and from which all oily matter has been carefully 

 separated (an old tooth-brush will serve for an example), it will be 

 found first to crack, and then to burn with a large and bright flame, in 

 consequence of the combustible gases into which the animal matter of 

 the bone is in part resolved. If the bone is taken out of the fire as soon 

 as it ceases to flame, it will be found to be of a bluish-black colour, from 

 the charcoal which is the residue of the decomposition of the animal 

 membrane. If the blackened bone be returned to the fire, the whole of 

 the charcoal is at length consumed, and nothing remains but the white 

 earth of the bone, commonly called bone-ash. 



If instead of a single one a heap of bones is employed, and a fire is 

 kindled in one part, it will spread by degrees to the whole heap, giving 

 out more or less flame, and a strong heat ; and in the treeless steppes of 

 Tartary, and the pampas of South America, the inhabitants make up 

 for the want of other fuel by burning the bones of their cattle, it being 

 considered that the bones of an ox will produce heat enough to cook its 

 flesh by. This, therefore, is another to be added to the many uses of 

 bone. But by burning bone in an open fire, no other product is 

 obtained from it except the ashes, while the horribly noisome odour of 

 the gas which escapes combustion, renders this process a sore nuisance 

 in any inhabited neighbourhood. 



The decomposition of bone by heat in close vessels, whereby the 

 action of atmospheric air is excluded, is well worthy of minute atten- 

 tion, both in consequence of the large scale on which it is carried on as 

 a process of chemical manufacture, of the importance of the products 

 obtained, and of the interest which it possesses in a scientific point of 

 view. 



The animal matter of bone is the only constituent part of this sub- 

 stance susceptible of decomposition by a heat brought up to low redness : 

 in considering, therefore, the action of close heat on bone, the earthy 

 ingredients may be considered as passive. The animal matter is either 

 a substance analogous to skin, or is a mixture of membrane and jelly : 

 the former opinion is supported by some of the most eminent modern 

 chemists, but it is of no sort of importance to our present purpose which 

 opinion is adopted, as all three substances are composed of the same 

 ultimate elements and nearly in the same proportions. The four simple 

 substances, then, of which the animal matter of bone is composed, are 

 carbon, hydrogen, nitrogen, and oxygen ; and of these the three latter, 

 when in an un combined state and at the usual temperature and atmo- 

 spheric pressure, are in the form of gas. Now, when it happens that 

 three substances, habitually gaseous, are combined with one naturally 

 solid, and when these four substances are likewise capable of uniting 

 together by two and threes, or, in other words, of forming binary and 

 ternary compounds, the attraction that holds together all the four is 

 easily disturbed by a moderate increase of temperature ; in consequence 



