April 14, 1870] 
it is combined. Even in that particular hydrogen com- 
pound, namely, marsh-gas, in which the amount of con- 
stituent hydrogen is largest, its proportion reaches only 
to 25 per cent., while among the many thousands of 
hydrogen compounds known to chemists, the following, 
and certain of their immediate congeners and isomers, 
are almost the only ones containing hydrogen to the 
extent of I1 per cent. and upwards :— 
Per-centage of 
constituent hydrogen. 
Marsh-gas . s nee 250 
Higher paraffins . 6 oO matt key Hyon) 
Line, 9 0 4 0 86 OR Oo 17°6 
INES 4 o 5 8 Oo ob 16°1 
Wigher alcohol bases . . . . . . 14 to 15°5 
Olefiant gas and homologues. . . . 14°3 
Eabeualcouolsian ech ae care ee ie LQntOmuA.O 
Wieonkaaintt og’ o 6 ob 6 @ 0 12°5 
VIVA? G co © ojo 6 0 MS b ¢ Biel 
From the circumstances, then, of hydrogen forming so 
small a proportion by weight of the compounds it helps 
to constitute, its proportion may conveniently be taken 
as unity, and the composition by weight of the above 
tabulated hydrogen compounds be preferably expressed 
as follows :— 
Parts by weight. 
Marsh-gas. . I hydrogen to 3'0 carbon 
Ethyl hydride 1 69 4'0 carbon 
Ammonia . I ” 4°7 nitrogen 
Methylamine. 1 aa 5°2 nitrogen + carbon 
Ethylamine I aC) 5°4 nitrogen + carbon 
Olefiant gas I oA 6-0 carbon 
Alcohol I 26 6°6 oxygen + carbon 
Wood-spirit I oH ‘O oxygen + carbon 
NEI G5: op 80 oxygen 
Now, while hydrogen is thus the least weighty, it is 
usually also the most mobile constituent of its several 
compounds. Accordingly, by acting on its several com- 
pounds with various reagents, it is possible to effect a 
removal of more or less hydrogen from them, often in the 
form of free hydrogen gas, more often in the form of 
some familiar hydrogen compound, such as water or 
muriatic acid. For instance, if muriatic acid itself, 
formic acid, ortho-phosphoric acid, and acetic acid, be 
each of them acted upon with either metallic sodium or 
caustic soda, taking care to keep the acid in excess, new 
compounds are produced, the composition of which in 
relation to that of the original acids may be expressed as 
follows :— 
Muriatic acid and sodium chloride. 
1 hydrogen + 35°5 chlorine 
23 sodium + o hydrogen + 35°5 chlorine 
Formic acid and sodium formiate. 
1 hydrogen + 6 carbon + 16 oxygen 
11°5 sodium + 4 hydrogen + 6 carbon + 16 oxygen 
Phosphoric acid and sodium phosphate. 
1 hydrogen + 10°3 phosphorus + 21°3 oxygen 
7°6 sodium + 3 hydrogen + 10°3 phosphorus + 21°3 oxygen 
Acetic acid and sodium acetate. 
1 hydrogen + 6 carbon + 8 oxygen 
5°7 sodium + $ hydrogen + 6 carbon + 8 oxygen 
It is observable that the new compounds differ in com- 
position from the original acids by a consecutively de- 
creasing gain of sodium, and by a corresponding loss of 
the whole, of one-half, of one-third, and of one-fourth the 
original hydrogen respectively; and there is this additional 
NATURE 
601 
point for consideration, that while in the case of formic acid 
and acetic acid it is not possible to obtain a compound 
differing from the original acid by a removal of one-third 
of its hydrogen, in the case of phosphoric acid it is not 
possible to obtain a compound differing from the original 
acid by a removal of one-half or one-fourth of its hy- 
drogen. But, by further treatment of phosphoric acid 
with caustic soda, another compound may be obtained, 
differing in composition from the original acid by a re- 
moval of two-thirds, instead of one-third, the original 
hydrogen; while, by treatment of acetic acid with chlorine, 
a series of new compounds may be obtained, differing in 
composition from the original acid by. a removal of one- 
fourth, and two-fourths, and three-fourths successively of 
the original hydrogen. Anyhow, the tendency of the 
hydrogen of formic acid is manifestly to break into 
halves, that of the hydrogen of phosphoric acid to break 
into thirds, and that of the hydrogen of acetic acid to 
break into quarters. 
Now, assuming the reacting units of the four acids to 
contain each but a single proportion, or one part by weight 
of hydrogen, there seems no reason why this hydrogen 
should in each case break up in a specifically different 
manner ; and, in other cases, in yet different manners, as 
into sixths, eighths, twelfths, and so on. But assuming 
the re-acting unit of formic acid to contain two propor- 
tions, that of phosphoric acid to contain three proportions, 
and that of acetic acid to contain four proportions of 
hydrogen, the reason of the different mode of breaking up 
becomes perfectly obvious, as shown in the following 
comparison with respect to composition of the original 
acids and their produced sodium salts; whereby it 
appears that a similar exchange of twenty-three parts by 
weight of sodium for one part by weight of hydrogen is 
effected in each of the four reactions. 
Muriatic acid and sodium chloride. 
1 hydrogen + 35°5 chlorine 
23 sodium + o hydrogen + 35°5 chlorine 
Formic acid and sodium formiate. 
2 hydrogen + 12 carbon + 32 oxygen 
23 sodium + 1 hydrogen + 12 carbon + 32 oxygen 
Phosphoric acid and sodium phosphates. 
3 hydrogen + 31 phosphorus + 64 oxygen 
23 sodium + 2 hydrogen + 31 phosphorus + 64 oxygen 
46 sodium + 1 hydrogen + 31 phosphorus + 64 oxygen 
Acetic acid and sodium acetate. 
4 hydrogen + 24 carbon + 32 oxygen 
23 sodium + 3 hydrogen + 24 carbon + 32 oxygen 
This, then, is the assumption actually made by chemists, 
and further warranted by many important considerations. 
For example, ammonia has the property of forming com- 
pounds with the above acids by direct combination or 
addition ; and the respective maximum quantities of the 
formic, phosphoric, and acetic acids, with which a given 
weight of ammonia can so combine, do actually yield 
twice, three times, and four times respectively the par- 
ticular weight of hydrogen that is yielded by the max- 
imum quantity of muriatic acid with which that same 
weight of ammonia can combine. Instead, therefore, of 
regarding the unit weights of all hydrogen compounds 
as including alike a single proportion of hydrogen, chemists 
regard them as including 1, 2,3,4,...... and x pro- 
