APPENDIX. 067 



tube after some oxide of copper, and then the tube is filled with 

 oxide of copper, and the analysis begun. When the substance 

 to be analyzed is very volatile, as alcohol, ether, &c., it is intro- 

 duced into a little glass bead, drawn out into a capillary point 

 by the lamp. This bead is slipt into the decomposing tube, and 

 covered in the usual way with oxide of copper, &c., and the ana- 

 lysis proceeded in. 



When the substance to be analyzed contains azote, precau- 

 tions are necessary to decompose certain compounds of azote 

 which are apt to be formed. It may make its escape in the state 

 of ammonia, or protoxide of azote, cr deutoxide of azote. The 

 ammonia will be decomposed into water and azotic gas in pas- 

 sing through the O7xide of copper in a state of incandescence. 

 The other two gases to be decomposed must be passed through 

 a considerable length of red hot copper turnings. The oxygen 

 of the gases combines with the copper, and the azote makes its 

 escape and may be collected over mercury. In such cases the 

 decomposing tube must be longer than ordinary, and must be di- 

 vided into four compartments, the first filled with oxide of cop- 

 per, the second with oxide of copper and the substances to be 

 analyzed, the third with oxide of copper, and the fourth with cop- 

 per turnings. 



We must begin with heating to redness the extremity of the 

 tube next the open end, and we must gradually bring the fire 

 along the tube, and the whole copper turnings and oxide of cop- 

 per must be red hot before we apply the heat to the mixture of 

 oxide of copper and the substance to be analyzed. Care must 

 be taken to keep the open extremity of the tube hot to prevent 

 any accumulation of vapour there, which would prevent the suc- 

 cess of the analysis. 



We may form an idea of the success of the analysis by the ap- 

 pearance of the carbonic acid gas as it is condensed in the po- 

 tash tube. If it comes over regularly and slowly, if it is quite 

 colourless and without smell, we may conclude that our process 

 is going on well. If, on the other hand, it be cloudy, coloured, 

 and, above all, if any oily matter make its appearance in the tubes, 

 we may conclude that the combustion of the matter under ana- 

 lysis is incomplete, and that portions of the carbon and hydrogen 

 are making their escape in the form of oily vapour. 



When an analysis is happily conducted the formation of gas 

 ceases all at once. When carbon has escaped combustion, and 



