594 EXPERIMENT STATION RECORD. 



easier to use, and because it was peculiarly suited to determining the 

 heat equivalent of many compounds which can not be determined at 

 all by the potassium chlorate method, for instance, those which are 

 easily volatilized. 



The principle on which the Berthelot apparatus is constructed is this: 

 A weighed quantity of the substance under investigation is burned in 

 an atmosphere of oxygen under high pressure, sometimes twenty-five 

 atmospheres, and the heat liberated is collected in a known quantity 

 of water. From the rise in the temperature of the water the heat 

 equivalent of the substance can be calculated. 



Details of the process may be found in the article quoted above. 

 Mahler's apparatus gives as good results as Berthelot's. It differs from 

 Berthelot's in that it is simpler in construction and hence easier of 

 manipulation. In each apparatus there is complete combustion to the 

 final decomposition products; in the case of albumen, for instance, 

 to carbon dioxid, water, nitrogen, and sulphuric acid. There are no 

 side products with the exception of a little nitric acid, but the quan- 

 tity of this can be easily determined, and the heat due to its formation 

 taken into account in the calcttlations. 



The purpose of this article is not so much to give results hitherto 

 unpublished as to collate what is known of the heat equivalent of those 

 compounds which are interesting from a physiological standpoint, so 

 that these facts will be available for practical use. The original data 

 are scattered through a considerable number of publications. All our 

 results here cited were obtained from combustions made with the Ber- 

 thelot apparatus, and are the mean values of several determinations 

 which agreed very closely with each other. They are also in most 

 cases compared with similar results obtained by Berthelot. 



I. PROTEIDS.^ 



Under ordinary circumstances the complete combustion of albumi- 

 noids is very difficult to accomplish. In the bomb, however, under a 

 high pressure of oxygen, and also by the potassium chlorate method, 

 which furnishes an abundance of oxygen, it is a very easy matter. 



The figures in the following table are derived entirely from our 

 determinations made with the Berthelot apparatus. A comparison of 

 these results with those obtained by the potassium chlorate method 

 follows later on. 



Each specimen of albuminoid substance used was as pure as it could 

 be obtained; that is, in each case it was extracted with ether to free it 

 completely from fat. 



Besides the heat equivalent, the elementary composition of each 

 substance was determined and the heat equivalent recalculated on an 

 ash-free basis. It should be borne in mind, in explanation of the 



'Jour. prak. Cbem., 2d ser., 44, p. 336. 



