APPENDIX. 685 



ing tube is still red hot, a considerable quantity of oxygen gas 

 should be passed through it, so as to burn all the charcoal depo- 

 sited, and to re-oxydize the copper, which has been reduced dur- 

 ing the process. 



3. To collect all the water, besides a tube filled with chloride 

 of calcium, there should be another filled with pumice, charged 

 with sulphuric acid. 



4. To collect all the carbonic acid gas, besides Liebig's potash 

 tube, there ought to be another filled with fragments of dry po- 

 tash, and another with fragments of pumice, charged with liquid 

 potash. The dry potash arrests the water with which the car- 

 bonic acid may be charged, in consequence of its passing through 

 the liquid potash in Liebig's tube. 



After the oxygen gas has completed the combustion, and the 

 whole has been allowed to cool, a quantity of dry air is to be 

 passed through the apparatus to displace the oxygen gas, and 

 prevent any augmentation of weight which might otherwise ensue. 



The analysis should be made slowly, and ought to occupy se- 

 veral hours. 



Thus Dumas' process of analysis is the same as that of Dr 

 Prout, with some improvements, which enable him to weigh the 

 water and the carbonic acid formed. When rightly conducted 

 the results must be accurate, and of course, however often re- 

 peated, the same proportion of constituents must be obtained. 

 But Dumas' process enables us only to determine the weight of 

 carbon and hydrogen contained in the organic body analyzed. 

 When that body contains azote we must have recourse to the 

 process of Varrentrapp and Will, which has been already de- 

 scribed. 



