388 Scientific Intelligence. [May, 
| 2. Test’ of Gallic Acid and Silver.—Gallic acid decomposes 
ammonio-nitrate of silver, or a solution of oxide, or of muriate 
of silver in ammonia, forming a very copious dense cloud and 
precipitate which does not entirely subside after along time. A 
very minute quantity of silver, or of gallic acid, may be detected 
and distinguished in this way. 
3. Preparation of Polychroite.—Polychroite* cannot be pre- 
pared by redissolving the dry extract of saffron in alcohol of 
sp. gr. 800. Ifthe extract be dried until it becomes brittle, a 
much weaker spirit must be used to redissolve it. When the 
alcohol is diluted to sp. gr. *840, the extract deliquiates, but 
remains undissolved at the bottom of the flask, exhibiting a very 
beautiful purple colour. Probably sulphuric acid only produces 
this colour in a solution of the extract by abstracting the water. 
4, Action of Sherry Wine on Iron.—A very respectable wine 
merchant of this town had a cask of sherry wine returned upon 
his hands in consequence ofa gradual deterioration in taste and 
colour. On emptying the cask, the iron part of a cooper’s tool 
(called a bracebit) was found at the bottom corroded in a remark- 
able manner at the steel extremity or head, but hardly, if at all, 
acted upon at the shank, which consists of malleable iron. 
Mr. Phillips, at p. 113 of his valuable ‘‘ Experimental Exami- 
nation of the London Pharmacopceia,” has stated, that “ the 
solubility of iron depends very much upon its softness.” But 
that very accurate experimenter and reasoner seems to have 
overlooked some solvents of iron besides tartar existing in sherry 
wine. Neither tartar nor vinegar has produced any effect upon 
a similar bracebit at all corresponding with that which took 
place in the sherry. I have had no opportunity of trying the 
gallic or malic acid, and think it better to state this trifling and 
probably useless fact than to offer speculation upon it. 
I remain, Sir, your obedient servant, 
CHRISTOPHER JOHNSON. 
P.S. Can you favour your distant readers with a more detailed 
character or even title of Dr. John’s Laboratorium than is to 
be derived from the article ‘Decomposition Chemical” in 
Napier’s Supplement to the Encyclopedia Britannica ? 
= Re—— 
A friend of mine who has just left Glasgow for Leipsic has pro- 
mised to bring me a copy of this and several other German che- 
mical books, which I have hitherto been unable to procure. 
When I receive it, I shall take an opportunity of giving an 
account of this work in a future number of the Annals.—T. 
* Thomson's Chemistry, iv, 50, 
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