Chemistry. Ixii 
of the combination is stopped. Indeed, when the -heat gets 
considerable, the chlorine which has already combined with the 
lime, seems to be again expelled. 
7. Persulphate of Iron.—The combinations of sulphuric acid 
and the peroxide of iron have been till lately almost entirely 
overlooked. I was fortunate enough to ascertain the existence 
of no fewer than four different salts composed of peroxide of 
iron and sulphuric acid, namely, 
Acid. Peroxide. 
1 Persulpate....... ... l atom + 1 atom 
2 Tripersulphate ...... 3 +1 
3 Quadripersulphate ... 4 + 1 
4 Subbipersulphate.... 1 + °2 
The first of these was a substance which was not susceptible 
of examination, as it was decomposed by being placed in con- 
tact with water. The tripersulphate is a reddish yellow deli- 
quescent salt, having a very astringent taste, and very soluble 
in water. It does not seem capable of crystallizing. The per- 
quadrisulphate forms transparent and colourless crystals, having 
much of the taste and the shape of alum crystals. It was dis- 
covered by Mr. Rennie. I afterwards examined and analyzed 
it, but did not succeed in obtaining it in crystals. Mr. Cooper 
has since ascertained the way by which it may be obtained in 
regular crystals, and has described its properties considerably 
in detail—(See Annals of Philosophy, xii. 298.) He calls it a 
perbisulphate; but itis obvious, from his analysis, that the con- 
stituents of his salt are the same as those of my perquadrisul- 
phate. The reason of this difference in our names is, that Mr. 
Cooper considers the weight of an atom of peroxide of iron to 
be 5, while I, to get id of the anomaly of the half atom, 
represent its weight by 10 or 5x2. I do not see any other way 
of reconciling the oxides of sodium, iron, nickel, and cobalt, with 
the atomic theory. To give iron as an example : 
An atom of iron weighs 3:5: 
Protoxide is composed of 3-5 iron + 1 oxygen=4°5 : 
Peroxide of 3:5 iron + 1:5 oxygen = 5: 
or 3°5 x 2 iron+ 1:5 x 2 oxygen = 10. 
If the weight of peroxide be 5, it is composed of an atom of 
iron, and an atom and a half of oxygen. If its weight be 10, 
it is composed of 2 atoms iron + 3 atoms oxygen; the con- 
stitution is the same; but the anomaly of the half atom dis- 
appears. 
8. Muriates.—From the experiments of Sir H. Davy and his 
brother, it has been concluded that when the muriates are ex- 
posed to a strong heat so as to drive off the whole of the water 
which they contain, they are converted into metallic chlorides. 
