of simple alimentary Substances, Sfc. 39 



the stop-cocks of the funnels, R R, and the stop-cock, S, of 

 the opposite syphon. 



Such is a general view of the apparatus, and the principles 

 of its operation : but perhaps a few practical remarks on some 

 of the circumstances to be attended to during its employment, 

 may not be deemed superfluous. 



The substance to be analysed may be placed in a small tray 

 made of platina foil, and introduced alone into the tube P, 

 and gradually submitted to the action of heat and oxygen gas ; 

 but this does not answer well with organic compounds, as a por- 

 tion of them is apt to escape combustion. Another method is 

 to mix the substance with pure siliceous sand, and to retain 

 the mixture in the centre of the tube by means of asbestos. 

 But this method often fails, except there be about an inch of 

 the oxide of copper at each end of the tube, which must be 

 kept red hot during the experiment, and in this case it suc- 

 ceeds completely with many substances. Another method, 

 and that which the most generally succeeds, is to mix the sub- 

 stance with peroxide of copper, to heat these together in the 

 tube in the first place, and afterwards to open the other stop- 

 cock and send the oxygen gas through the ignited and par- 

 tially reduced oxide, by means of which it again becomes 

 peroxidized ; and any portion of the substance that had es- 

 caped complete combustion in the first part of the experiment, 

 is now completely burnt. This last method is also that em- 

 ployed when it is required to determine the quantity of carbonic 

 acid gas yielded by a given quantity of any substance ; only 

 in this case, of course, oxygen gas is not required, and the 

 contents of the tube P, must be taken out and well triturated, 

 and subjected to heat a second time. If it should be required 

 to analyse the gas formed, one method of removing it from 

 the tube I, is represented at fig. 5; and others will readily 

 occur to the practical chemist. 



The following are some of the advantages of this apparatus, 

 and mode of analysing organic compounds. In the first and 

 chief place, there is nothing to be apprehended from moisture. 

 Whether the substance to be analysed be naturally a hydrate, 

 or in whatever state it may be with respect to water, the results 

 will not be affected ; and the great problem, whether the hy- 

 drogen and oxygen exist in the substance in the proportions 

 in which they form water, or whether the hydrogen or oxygen 

 predominates, will be equally satisfactorily solved, and that 

 (of course within certain limits), independently of the weight 

 of the substance operated on*. When however it is the ob- 

 ject 



* It is to be observed, that, throughout the experiments, great care is 



taken 



