150

APPENDIX.

fractions ; if not, they are whole grains. The composition ofSulphate of Lime may be expressed also as—

Lime . . *412 4*12 41*2 412

Sulphuric acid . *588 5*88 58*8 588

1,grain. 10 graitiB. 100 grains. lOOOgrains.

In all the analyses given in the following pages, no fractionsare used; the composition of everything is given as it would beobtained if 10000 or 100000 grains were analysed.

Chemists are constantly in the habit of speaking of atoms, pro-portions, combining numbers, and similar terms ; it will be wellbriefly to describe what is meant by these terms. It has beenalready stated that the composition of all compound substances isdefinite (84) ; that a certain weight of Carbon , for example, canonly combine with a fixed quantity of Oxygen to form Carbonic Acid (86). Let us observe what relation there exists betweenthe quantity of different substances which can combine together.It is found that one grain of hydrogen (for hydrogen, though agas, can be readily weighed) will combine with eight grains ofOxygen to form nine grains of steam, and this relative proportionbetween the two elements of water is pei*fectly invariable. Onegrain of Hydrogen can combine with exactly sixteen grains ofSulphur to form seventeen grains of Sulphuretted Hydrogen(117), or, with six grains of Carbon , to form seven grains ofCarburetted Hydrogen (80). These numbers, then, express thequantity of each of these substances which can combine with oneanother, for, of course, it is perfectly the same whether we takea grain, an ounce, a pound, or any other weight. But this is notall; the number thus found for Carbon , namely six, is not merelythe quantity of that substance which could combine with one ofHydrogen, but represents the quantity of Carbon which can com-bine with eight parts of oxygen, to form Carbonic Oxide (87), orwith twice eight, 16, parts of Oxygen to form Carbonic Acid ; and,again, eight parts of Oxygen is not merely the quantity which cancombine with one part of Hydrogen, or with six of Carbon , butalso exactly the quantity which is able to combine with a certain