A HARD-WORKING DIET. 345 



see p. 336). The Hydrogen and Carbon of the fat 

 will be found to form water and carbonic acid, just 

 as those from the other sources. When fully oxi- 

 dized they always do, whatever the source from 

 which they come, and whether that source be in a 

 state of gas or liquid or solid. 



This is a rough and ready way of showing that C Fats and oils. 

 and H are present in fats. Compounds of Carbon 

 and Hydrogen are called hydro-carbons. Fats and oils 

 are all in the main hydro-carbons, though not always 

 pure. Every one is familiar then with compounds 

 of Carbon and Hydrogen, though the names may be 

 new to them. When the amounts of C and H have Compounds 

 to be known by weight, the simple apparatus here ar e separated 

 used does not suffice. The principle of proceeding {jn 

 is however the same that of converting into Car- 

 bonic acid and water, but this has to be done in a water - 

 way that admits of their being weighed. 



As the composition of Carbonic acid is always 

 everywhere the same (three-elevenths Carbon and 

 eight-elevenths Oxygen) it is easy to calculate how 

 much Carbon there is in a known weight of Carbonic 

 acid, and as the composition of water is always every- 

 where the same (one-ninth Hydrogen and eight-ninths 

 Oxygen) it is easy to calculate the amount of Hydro- 

 gen in a known weight of water. If therefore we By weighing 



the amount 



want to know the weight of Carbon and Hydrogen in of Carbonic 

 any Hydro-Carbon, we get at them by separating out wa ter we 

 the Carbon as Carbonic acid, and the Hydrogen as 

 water. This is the simple method that has been 

 followed in investigations of the AMOUNTS OF c f ta ] n weight 



of a Hydro- 



CARBON AND HYDROGEN IN A HYDRO-CARBON Carbon. 

 COMPOUND. 



