466 Scientific Intelligence. [JunE, 
VIII. On the Discovery of Bipersulphate of Iron. 
By Charles Sylvester, fe. f 
(To Dr. Thomson.) : 
SIR, Derby, April 5, 1819. 
In the Annals of Philosophy, vol. xii. p. 462, you gave an 
account of the persulphates of iron, in which you stated your 
discovery of a quadripersulphate of iron, and you gave your 
opinion of the probable existence of several others, amon 
which was included the bipersulphate. This latter salt I have 
been in the habit of preparing for the last,seven years, and it 
has been used in a liquid form as a tonic mixture to a consider- 
able extent during that period, particularly at Derby, Notting- 
ham, and Sheffield. It has also been prescribed by my friend 
Dr. Robinson, Physician to the London Hospital. 
When the solution (which was generally made to the same 
strength) by any accident became more than usually concentrated, 
a white pearly precipitate was always formed, giving the liquid 
the appearance of thick soap suds. This gave me first the idea 
that some crystallized compound was formed. On evaporating 
the clear solution I always had the same white precipitate, but 
' did not for some time obtain the salt in regular crystals. 
By spontaneous evaporation in a broad shallow vessel, I 
rocured the salt in distinct crystals, which were octahedrons. 
i showed the salt in this state to a number of my chemical 
friends, about three years ago, and have made it in small quan- 
tities since that time 
It was my intention to have published an account of it as soon 
as I had contrived an apparatus for making it with facility. 
This, however, I have been prevented from doing by my other 
engagements, and I should not at the present time have referred 
to the subject had it not been for the appearance of an account 
of this salt in the number of your Annals for April, by Mr. Tho- 
mas Cooper; in which he states that he has formed this salt in 
octahedral crystals, confirming your opinion of its probable 
existence. 
It now becomes necessary for me to state a circumstance, 
which, however it may appear to charge Mr, C. with want of 
candour, I shall entirely acquit him of any improper motive. 
In the latter end of last summer, I showed the salt in question 
to Mr. Cooper, telling him that it was a bipersulphate. The 
crystals were not large, but with a glass the octahedrons could 
be distinctly seen. 1 did not tell him the process, but the name 
would easily lead toit; since nothing more is necessary by the 
account he has given of it than to boil together sulphuric acid 
and the peroxide of iron in the proportions to make two atoms of 
acid to one of base. I am, your obedient servant, 
CHARLES SYLVESTER. 
