© 
A HARD-WORKING DIET. iI 
somewhat complicated. But it is really not difficult, 
it requires only a little careful attention, principally in 
guarding against a confusion of ideas from attaching to 
terms meanings not intended; and it is far easier to 
follow when practical acquaintance has been made with 
C, H, O, and N by even simple experiments with them. 
It may help to clear away a preliminary difficulty to CHON 
: : cannot be 
mention that although, as just stated, every one has recognised as 
se eee ] ts 1 
been living on C, H, O, and N, all their lives, they the com. 
pounds that 
form our 
food. 
could not see the individual elements, not even the 
solid carbon, in the compounds as they occur in 
foods. These can only be got at by separating them 
out by chemical analysis at different temperatures. 
It is just the same as with many familiar things we Just as 
: : : : copper and 
donot use as food. In brass, forexample, which is an jinc cannot 
be individu- 
alloy of the elements copper and zinc, the copper and allyncces 
zinc cannot be recognised as such, though they can be M¢¢ im brass. 
separated out ; or in bronze the tin and copper cannot 
be recognised, though they can be separated out. 
Elements cannot be recognised in a chemical 
compound, though they may be in a mechanical 
mixture. A simple experiment that can be made on The meaning 
of the term 
chemical 
the difference that is meant by the terms “ mechanical Compound. 
a shovel over a fire will serve to illustrate what is 
mixture” and “chemical compound.” Get some 
fine copper filings and some powdered sulphur well 
mixed together on a sheet of paper. The copper 
and the sulphur can still be separately distinguished— 
if not with the unaided eye, they can be with a 
magnifying glass and the sulphur can be washed 
away. ‘This is called a “mechanical mixture.” But 
put such a mixture on a shovel over the fire till it 
glows, and on cooling there will be found a black 
