1815.} On Iodine. 187 
and which allows that acid to escape by the action of a moderate 
heat. In the same way, when phosphuret of potassium is dissolved, 
phosphureted hydrogen gas is disengaged. The water then in these 
different circumstances is decomposed: in the first case, in conse- 
quence of the affinity of potassium for oxygen, and of sulphur for 
hydrogen; and in the second, in consequence of the same affinities, 
togetlier with that of phosphorus for oxygen, since at the same time 
phosphorous acid is formed. Further, 1 have already pemarked that 
among the chlorurets, iodurets, and sulphurets, it is those one of 
whose elements has more affinity for oxygen than the other for 
hydrogen, that are soluble in water. Hence after the unequivocal 
existence of hydro-chlorate and hydriodate of magnesia; after the 
proofs which I have given that water, either in dissolving a chlo- 
ruret, or in abandoning it, may be decomposed or formed by thé 
same forces that determine the double saline decompositions; and 
after the analogies which I have just stated, I think we may admit 
that most of the chlorurets, iodurets, and sulphurets, in solution in 
water, those at least whose metals have a great affinity for oxygen, 
may be considered as hydro-chlorates, hydriodates, and hydro-sul- 
phates. I do not, however, deny the existence of the chlorurets, 
&c. in solution in water. On the contrary, I admit as a principle 
that we ought to have a chloruret or a hydro-chlorate in solution, 
according as the forces which act in order to decompose water are 
smaller or greater than those which keep its elements united. 
Nore B, 
On Acidity and Alkalinity. 
All the combinations which bodies form may be divided into two 
sets. In the one there is perfect neutrality ; in the other, acidity or 
alkalinity. : 
Neutrality may not only exist in the saline combinations, but 
likewise in many others. Thus the ethers formed by the combina~ 
tion of an acid with alcohol, the soaps with an alkaline or acid basis, 
are so many compounds in which the respective properties of the 
constituents disappear completely. In the acid or alkaline combina-~ 
tions, on the contrary, the peculiar properties of ong of the consti- 
tuents still show themselves. 
From the idea of neutrality derived principally from the saline 
combinations, we regard, as performing the function of an alkali, ° 
all the bodies which saturate either completely or in part the pro- 
perties of acids ; and as acids, all bodies that saturate the propertie 
of alkalies. We consider, further, the neutral state as resulting 
from a certain constant ratio between the body which possesses the 
properties of acids, and that which possesses those of alkalies. In 
every other ratio the compound is acid or alkaline. But in all cases 
the acidity or alkalinity which is in excess is less than before the 
pombination; and this excess may be exactly measured by the quan: 
