On definite Proportions. 165 
vention of one or more other bodies; and since these perhaps 
never, or at least very rarely, exhibit combinations at a minimum, 
we are obliged to seek for these minima in more complicated 
modes of combination. It will be difficult to discover the true 
minimum ; but every good experiment, made with this view, will 
be productive of interesting consequences. ‘The subsalt of iron, 
just analysed, may serve as an example in illustration of this re- 
mark. If we should hereafter discover no combination of the 
sulphuric acid with a greater quantity cf iron in the salts of the 
protoxide or oxide, and should the prepertion of the sulphur to 
the iron, found in this experiment, be the greatest common di- 
visor of all the numbers expressing the proportions which are 
found in the mixtures of sulphur with iron, we might be allowed 
to hope that we had feund the minimum of sulphar with which 
iron could combine; 100 parts of iron here bemg united with 
14-66 of sulphur. In the magnetical pyrites, called the sulphuret 
at a minimum, because it is the lowest stage of combination 
which can be separately exhibited; or in the neutral sulphate of 
the protoxide of iron, 100 parts of iron are combmed with 
14-66 x 4=58-64, in the sulphate of the oxide with 14-66 x6= 
87-96, and in the common pyrites with 14°66 x 8=117-28 parts 
of sulphur. Consequently these are multiples of the lowest pro- 
portion by 4, 6, and 8, and we find that these multiples agree 
with the results of the experiments as far as the thousandihs of 
the whole. It may be supposed that the multiple by 2, which: 
is here wanting, still exists, although perhaps in a combination 
which is yet unknown ; for instance, in a subsalt of an oxide, in 
which the sulphuric acid and the exide contain equal pertions 
of oxygen. If now 14:66 parts of sulphur were the smallest 
quantity with which 100 parts of iren could combine, it would 
follow, that no subsalt of the protoxide of iron could exist. But 
if, on the contrary, such a subsalt should be discovered, 14°66 of 
sulphur for 100 of iron would not be the minimum, and it could not 
be greater than 4-9, which would be the greatest common divisor 
of all the combinations of sulphur with 100 of iron. Nearly in 
the same manner I have attempted to find the minimum of oxy- 
gen in the combinations of carbon; but in order to discover - 
which of the various numbers that might represent the quantity 
of oxygen, is the true minimum, a great number of experiments 
would be necessary, which would require the labour of several 
years before they could afford a tolerably certain result. 
2. Subsulphate of the Oxide of Copper. 
1 precipitated some sulphate of the oxide of copper with caustic 
ammonia, taking care not to throw down the whole of the oxide, 
and heated 10 grammes of the precipitate, well washed and 
L3 dried, 
