the different hrnds of' Coal. 6S 



by chemists for the analysis of vegetable matters. It is known 

 to consist of three glass tubes, connected by two tubes of caout- 

 chouc, which arc placed, the one between the first and second 

 tubes, the other between the second and third. The first tube, 

 destined to receive immediately the action of the heat, contained 

 a mixture of the body to be essayed with deutoxide of copper, 

 prepared by means of nitrate of copper. The second tube con- 

 tained muriate of hme completely dried. The third tube, des- 

 tined to receive the gases, was very narrow, and graduated by 

 an accurate division into tenths of a cubic inch, Rhine measure. 

 This latter tube conducted the gases into a mercurial apparatus. 

 The quantity of gases developed, was reduced to the tempera- 

 ture of zero, and to the barometrical pressure of 28 inches. 

 Their volume was determined under these conditions. For the 

 absorption of the carbonic acid gas, caustic ammonia was em- 

 ployed. With regard to the residue of gases not absorbed, 

 their volume was subtracted from the total mass of gas, accord- 

 ing to the reductions indicated, and it was the difference that 

 made known the real volume of carbonic acid gas. But the au- 

 thor did not enter into the examination of the residuum. Was 

 this pure azote, which did not seem probable to him, or was it 

 rather a mixture of azote with atmospheric air, and carbonic 

 oxide gas, or even carburetted hydrogen gas ? With regard to 

 this, the author is not able to pronounce with certainty ; he 

 thinks, however, that he avoided the disengagement of carbonic 

 oxide gas, by not filling the first or decomposition tube in the 

 usual manner. The following are the peculiar precautions 

 which he took. 



The first tube had a diameter of from 2.5 of a line, to 9,.65, 

 and a length of about nine inches. It was shut below, and open 

 above. There was first introduced into it a certain quantity of 

 oxide of copper, which occupied the bottom of the tube ; above 

 this, was formed a layer of oxide of copper, mixed with the sub- 

 stance to be decomposed ; then a new layer of oxide of copper, 

 without admixture, and so alternately, until there were six lay- 

 ers of mixture in the tube, contained between two layers of oxide 

 of copper, which occupied its two extremities. 



This done, at each of the two extremities of the tube, above 

 and below, there was placed a lighted lamp. The tube was thus 



