664 APPENDIX. 



cium gives the quantity of water formed, and the increase of 

 weight in the potash tube gives the quantity of carbonic acid 

 formed. From these two it is easy to calculate the weight of 

 hydrogen and carbon in the substances under analysis. For the 

 hydrogen is one-ninth of the weight of the water, and the carbon 

 three-elevenths of that of the carbonic acid. 



Professor Liebig in the same paper showed how an estimate 

 might be formed of the quantity of azote contained in the sub- 

 stance to be analyzed by subjecting it to a second analysis, in 

 which the tube with the potash was left out, and the mixture of 

 azotic and carbonic acid formed received in a set of ten or twelve 

 graduated tubes filled with mercury, and standing on the mer- 

 curial trough. The ratio of the carbonic acid and azotic gas in 

 each is determined by absorbing the carbonic acid gas ; and that 

 ratio gives the ratio of the atoms of azote and carbon. Suppose 

 one volume azote and four volumes carbon, then for every atom 

 of azote there are four atoms carbon. From these data, know- 

 ing the specific gravities of azotic and carbonic acid gases, it is 

 easy to deduce the weight of azote in the substance under ana- 

 lysis. 



It was this apparatus of Liebig which gave popularity to orga- 

 nic chemistry. The mode of analysis appeared easy and simple. 

 Liebig devoted his laboratory to organic investigations. His 

 pupils increased in number, and he started a periodical work en- 

 titled Annalen der Pharmacie, in which the labours of his nume- 

 rous pupils were consigned. Organic analyses increased in num- 

 ber, and almost every animal and vegetable principle was subjected 

 to this important scrutiny. Facts were increased prodigiously, as will 

 be evident to the most careless observer, if the contents of the two 

 volumes regarding animal and vegetable substances be inspected. 



But the defects of oxide of copper as a means of analysis, 

 pointed out by Prout, especially its property of absorbing mois- 

 ture and air with avidity, rendered it desirable that some substi- 

 tute free from these defects should be discovered. Liebig point- 

 ed out a substitute in 1837 in chr ornate of lead, the employment 

 of which was first tried by Mr Richardson.* It is prepared by 

 precipitating a salt of lead by bichromate of potash. The preci- 

 pitate is well-washed, dried, and melted in a Hessian crucible. It 

 is then pulverized, and, being put into a stoppered bottle, is ready 

 for use. This salt has the important property of neither absorb- 



* Annalen der Pharm. xxiii. 58. 



