668 APPENDIX. 



is mixed with the oxide of copper, the evolution of gas goes on 

 for a long time. In such cases we should always mistrust the 

 accuracy of our analysis. 



M. Dumas's method of determining the quantity of azote in a 

 body under analysis is somewhat different from that of Liebig, 

 and when the combustion is complete (which, however, is diffi- 

 cult,) seems quite accurate. It will be worth while to state it 

 here : Into the bottom of the decomposing tube some grammes 

 of pure dry carbonate of lead are introduced. Above it, b, is 

 put a mixture of oxide of copper and copper turnings. In c is 



1 I 



put a mixture of oxide of copper, and the body to be analyzed ; 

 in e ten or twelve grammes of oxide of copper mixed with some 

 turnings ; while the outer portion is filled with copper turnings. 

 The tube is connected with a mercurial trough, exhausted, and 

 then a portion of the carbonate of lead is heated. The carbonic 

 acid evolved drives out the common air in the tube, taking its 

 place, and the process is continued till pure carbonic acid passes 

 into the mercurial trough, and is totally absorbed by the potash 

 placed for the purpose. The whole portion e of the tube is then 

 made red hot, and the portion c being gradually heated the azotic 

 gas evolved is passed into the gas-holder over mercury. When 

 it ceases to come over heat is applied to the rest of the carbonate 

 of lead in , which carries with' it all the azotic gas remaining in 

 the tube. The carbonic acid is absorbed by the potash, and no- 

 thing remains but the azotic gas. Its volume is measured, and 

 its specific gravity being 0-9722, it is easy to determine its weight. 

 This method is very good ; but another has been lately contrived 

 by Drs Will and Varrentrapp, which will be stated below. 



The hydrogen is determined by means of dry fused chloride 

 of calcium, as first proposed by Berzelius. The mixture of oxide 

 of copper and the substance under analysis is put into the com- 

 bustion tube. This tube is luted, by means of an excellent cork, 

 to a long tube filled with fragments of chloride of calcium, and 

 this long tube is attached to a small air-pump, or rather syringe, 

 The air is exhausted, and then allowed to flow back through the 



