9 
Mr Herschel on the Hyposulpliurous Acid. 
posed and colourless, similar to that of sulphate of magnesia, 
which I could not account for. I at first suspected the pre- 
sence of that salt, from having possibly employed a magnesian 
limestone, or from some accidental source, but soon satisfied 
myself to the contrary. The liquid had lost its property of pre- 
cipitating iron or copper from tlieir solutions in the state of sul- 
pliurets, though it still gave a copious precipitate to the car- 
bonated alkalis, and of course retained lime in some state of 
union with an acid, which could not be either the sulphuric or 
sulphurous^ neither of these forming soluble salts with lime. 
The inquiry now became highly interesting ; the experiments 
of Berthollet, as reported by Dr Thomson in the 2d volume 
of his Chemistry (4th edition, p. 52), on the decomposition of 
this identical solution by atmospheric exposure, as well as those 
of the latter eminent chemist himself on the similar compound 
of potash (Chem. vol. iii. p. 385), expressly with a view to this 
point, appearing definitive as to the formation of mere sulphates 
under these circumstances ; while a few trials were sufficient to 
establish marked distinctions between the acid in question, and 
any with v^^hich I was then acquainted. 
Some time after, and when most of the experiments I have to 
relate were made, and a great part of the present essay Avritten, 
a friend pointed out to me the folio AAung passage in the 5th edi- 
tion of the work above mentioned : Besides the two acid com- 
pounds of sulphur and oxygen, we have the fullest evidence of 
the existence of a third, composed of one atom sulphur -}- one 
atom oxygen, or of sulphur 100 q- 50 oxygen by weight, to 
which the name of Hyposulpliurous Acid may be giA^en. This 
acid has not hitherto been obtained in a separate state, but can 
be readily enough obtained united to bases.” I immediately 
procured the edition in question, but found little farther satis- 
faction. The distinctive characters of the acid, AAliich are very 
peculiar, are not mentioned ; and only one or two of the hypo- 
sulphites described in a very general and imperfect manner, 
Avhile the reader is referred to a paper by Gay Lussac, in the 
85th volume of the Amiales de Chimie, Avhich I have not yet 
been able to procure ; but, from the knoAvn accuracy of Dr T. 
as a compiler, I haA^e little doubt he has extracted all that is con- 
tained on the subject in the French chemist’s memoir. On this 
