292 PHYSIOLOGY AT THE FARM. 



carbon into carbonic acid, and the whole of its hydrogen into 

 water : in which case the simple determination of the amount 

 of carbonic acid and the amount of watery vapour collected, 

 together with the amount of oxygen afforded, would suffice to 

 show how much carbon, how much hydrogen, and how much 

 oxygen, were in the weight of the substance submitted to 

 analysis. The plan was found to give very satisfactory results. 

 The substance finally chosen was the black oxide of copper 

 (C u = 39.7), which may be exposed to a very high tempera- 

 ture by itself without undergoing any change, but which, when 

 heated with combustible substances, parts readily with oxygen. 

 Thus, by weighing a quantity of this oxide before and after the 

 experiment above described, the quantity of oxygen which had 

 united with the elements of the organic body under examination 

 was at once ascertained. The analysis of the ashes gave the 

 ultimate elements present belonging to the second head above 

 indicated. 



Nearly the same observations apply to an organic substance 

 from the animal kingdom, with this exception, that, owing to 

 the general presence of nitrogen, it affords by destructive heat, 

 besides such products as are so obtained from a vegetable 

 substance, ammonia, cyanogen, and free nitrogen. The exact 

 analysis by black oxide of copper is conducted on a like plan. 



Ultimate Elements of the First Order. 



Oxygen. Oxygen is the most abundant substance in nature. 

 It exists everywhere so that the difficulty is rather to discover 

 natural bodies in which there is no oxygen than to enumerate 

 those of which it is a constituent. It makes nearly a fourth 

 part by weight of the atmosphere, it constitutes eight-ninths 

 of the whole weight of the waters of the globe, and nearly a 



