A HARD-WORKING DIET. 15 
see p. 6). 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 
of C and H 
to be known by weight, the simple apparatus here are separated 
oes hs : t by oxida- 
used does not suffice. The principle of proceeding tonite 
j > Carbonic 
is however the same—that of converting into Car- (iO 
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 zy weioene 
want to know the weight of Carbon and Hydrogen in of Carbonic 
acid and of 
any Hydro-Carbon, we get at them by separating out water we 
the Carbon as Carbonic acid, and the Hydrogen as waste ore 
water. This is the simple method that has been and of H 
present in a 
followed in investigations of the AMOUNTS oF cettain eee 
of a Hydro- 
CARBON AND HYDROGEN IN A HYDRO-CARBON Carbon. 
COMPOUND. 
