34 Dr. Prout on the ultimate Composition 



The modes in which chemists have attempted to combine 

 oxygen with the hydrogen and carbon of vegetable substances 

 have differed very considerably. The illustrious Lavoisier 

 attempted their union by burning the substance at once in 

 oxygen gas, a method subsequently followed by Saussure and 

 others. Afterwards the metallic oxides were employed for 

 the purpose ; and Berzelius in particular informs us, that so 

 early as 1807 he had tried the oxide of lead, but did not suc- 

 ceed with it*. In 1811, Gay Lussac and Thenard published 

 the analysis of different organic substances made by means of 

 the chlorate of potash ; and, considering the nature of the ap- 

 paratus they employed, they obtained admirable approximate 

 results f. Berzelius, in 1814, published an elaborate paper 

 on the subject of vegetable analysis, in which he likewise em- 

 ployed the chlorate of potash, but in quite a different manner; 

 and to this celebrated chemist I believe we are indebted for 

 the improvement subsequently adopted by most of his suc- 

 cessors, of introducing the mixture of the substance to be 

 analysed, and the oxide, into a narrow tube, and submitting 

 the different portions of it to heat in succession. The results 

 of Berzelius were in general more accurate than those of his 

 predecessors, especially as far as related to the quantity of 

 carbon, but his method was not well adapted for determining 

 the proportion of hydrogen J. In 1816, Gay Lussac seems to 

 have thought of employing the oxide of copper for the pur- 

 poses of analysis §, the introduction of which undoubtedly 

 constituted one of the greatest improvements hitherto made in 

 organic analysis ; and the use of which has continued to the 

 present time, and will perhaps never be entirely superseded. 

 The oxide of copper has however some disadvantages, which 

 it is one object of the present remarks to point out ; another 

 is, to propose a form of apparatus free from most of the ob- 

 jections to which those hitherto in use have been more or less 

 liable. 



There are two methods of arriving at the quantity of water 

 formed during the combustion of an organized substance ; 

 either actually to collect and weigh it, as Berzelius did, or to 

 estimate the quantity by the loss of weight sustained by the 

 tube after the combustion. The latter in general is the best 

 method, and was that adopted by me from the first : it has 

 since been followed by Dr. Ure, and others ||. Whichever 

 method is adopted, it obviously becomes necessary that no 



* Annals of Philosophy, iv. 403. t Recherches Physico-chimiques, ii. 265. 

 % Annals of Philosophy, iv. 323. § Annates de Chimie, xevi. 306. 

 || Phil. Trans. 1822. p. 457- 



extraneous 



