Natural History. 201 



bones be subjected for a time to a temperature of 260° or 280° F., 

 or to high pressure steam, they break more readily; but then a part of 

 the fat is altered, and the process should only be employed for those 

 bones which contain no fat, or are old and dirty. 



The preservation of the bones becomes an important matter, 

 especially as they readily putrefy, and then one part of their jelly 

 forms ammonia, which, combining with the undecomposed jelly, 

 takes from it the property of gelatinizing 1 when cold, and renders it 

 soluble in water. They should first be freed from the fat, which 

 otherwise in time renders them rancid. The broken bones boiled 

 with water, yield much fat, but still retain enough to render them 

 rancid. The process of separating the fat by saponifying it with 

 soda, is not a good one, because the gelatine is also altered. Even 

 the fresh bones may be preserved by being salted, but the products 

 are injured, and the process expensive. The best method is that 

 adopted by Plowden, for the preservation of meat, namely, dipping 

 them into a strong solution of the juice of meat, or jelly, and drying 

 them in the open air. For this purpose, a solution, containing one- 

 fifth of dry jelly, was heated up to 180° or 190° F., and the bones, 

 previously cleaned, broken, and freed or not from fat, dipped into it ; 

 they were then dried upon nets in the air, and again dipped, &c, 

 once or twice more, to thicken the film of gelatine. They were then 

 perfectly dried in a stove at temperatures from 70° to 80° F. 



Papin proposed to separate the jelly from bones by the use of high 

 pressure steam, but this process gives an empyreumatic flavour, and 

 destroys gelatinizing power ; long boiling of the rasped bones in 

 water, at common pressures, is tedious and expensive, and does not 

 give all the jelly. Fifteen years ago M. D'Arcet proposed to use 

 acids in extracting the jelly, and thinks it was only because the pro- 

 cess was not put into clever hands that it failed. 



Whilst studying the process of Papin, M. D'Arcet removed the 

 objections to it, by improvements in the apparatus required, for 

 which he took out a patent. The most advantageous method ap- 

 pears to consist in exposing the bones to the action of steam, 

 having a feeble pressure, the vapour condensing in the pores of 

 the bone, first expels the fat, and then successively dissolves the 

 gelatine. 



The presence of the fat in bones complicates the process ; under 

 the influence of high pressure steam the carbonate of lime present 

 acidifies it, and forms an insoluble soap, which opposes the solution 

 of the gelatine. It is therefore necessary, first, to separate the fat, 

 which is done either by boiling the broken bones in a covered caul- 

 dron with water in the usual way, or in exposing them to steam of 

 ordinary pressure. 



The extraction of the gelatine by uncompressed steam requires 

 at least four days. The crushed bones freed from fat, or not, are to 

 be placed in a cylindrical basket of tinned iron-wire, which nearly 

 fills a metallic cylinder, in which it is to be suspended. The latter 



