662 APPENDIX. 



ing the mixture of oxide of copper and the body to be analyzed, 

 and the oxygen gas was driven backwards and forwards through 

 it, till the combustion was at an end, and till the oxide of cop- 

 per, partially reduced, had recovered its original quantity of oxy- 

 gen. The apparatus was then allowed to cool. The oxide of 

 copper will imbibe all the moisture and air which it contained 

 before the experiment began. The volume of gas in the tube is 

 now measured with accuracy. If it is unaltered it follows that 

 the oxygen and hydrogen in the body analyzed are in the pro- 

 portion to form water. The volume of carbonic acid gas is then 

 ascertained from which the weight of carbon is easily deduced. 

 Subtracting this from the original weight of the substance under 

 analysis, the remainder is the hydrogen and oxygen in the pro- 

 portion which constitutes water. 



If the volume of gas be increased it is a proof that the oxygen 

 in the substance analyzed is more than what is necessary to con- 

 vert the hydrogen into water ; and the increase of volume gives 

 the additional quantity of oxygen present. 



If the volume be diminished it indicates that the hydrogen in 

 the substance under analysis is more than v/hcit is. requisite to 

 convert the oxygen into water. And twice the volume of di- 

 minution gives the volume of hydrogen thus in excess. 



This method is susceptible of great accuracy. But it requires 

 much accuracy in measuring the vc!i:mes of oxygen gas and 

 carbonic acid gas evolved. And as tha v/jiglit cf the carbon, 

 and even of the hydrogen, is deduced from the volume, it is ne- 

 cessary for accuracy that the specific gravity of these gases should 

 be correctly known. 



By this process Dr Prout analyzed twenty-one vegetable sub- 

 stances (all without azote), and the result in his hands was ex- 

 ceedingly near the truth. But the complexity of his apparatus, 

 and the jdifficulties attending minute measurement cf the vo- 

 lumes of the gases employed or formed, have prevented other che- 

 mists from following his method. We do not know, therefore, 

 how it would succeed in the hands of chemists less cautious and 

 scrupulously accurate than Dr Prout. 



The attention of Professor Liebig to the analysis of organic 

 substances seems to have been drawn by this memoir of Dr Prout. 

 In 1830, he published a critical examination of Dr Prout's ap- 

 paratus, pointed out its inapplicability to the analysis of substances 



