xl Historical Sketch of the Prgsical Sciences, 1818. 
of chemists to the specific gravity of the best Japan copper, 
which I found only 8-434. It is merely valuable, because it 
enables us to correct the statements of Cronstedt and Bergman 
upon this subject. They made the specific gravity of Japan 
copper above 9. Now the specific gravity of the very purest 
copper which can be procured is somewhat under 9, even when 
it has been hammered or passed between rollers.—( Annals of 
Philosophy, xiii. 224.) 
I may allude also to the specimen from the mint which I ana- 
lyzed, and which I found a mixture of protoxide of copper, oxide 
of iron, and sand. It is valuable merely, because it shows that 
the protoxide of copper may, in certain circumstances, be formed 
by the application of heat to metallic copper. 
M. Chaudet, to whom we owe a set of experiments on the 
possibility of separating tin from antimony and bismuth by means 
of muriatic acid, experiments of which an account has been 
given in a preceding historical sketch, has more recently made a 
set of experiments to determine whether the same acid be capable 
of separating tin from copper when the two metals are alloyed 
together. The result was, that in whatever proportion the two 
metals are alloyed, they cannot be accurately separated by 
muriatic acid. In general the copper prevents the tin from 
dissolving so readily in muriatic acid as it would have done had 
it been pure. Hence the last portions consist of copper still 
alloyed with a notable proportion of tin,—(See Ann. de Chim. et 
Phys. vu. 274.) 
13. Silver—In the Annals of Philosophy, xii. 143, is given a 
very easy method of reducing silver from its chloride to the 
metallic state, for which we are indebted to M. Arvedson. The 
method is this: put into a conical glass a quantity of granular 
zinc, cover it with chloride of silver, and then pour it on some 
diluted sulphuric acid. The hydrogen gas evolved speedily 
_reduces the silver to the metallic state. I have verified this 
method, and found it to answer perfectly well. 
14. Platinum.—Mr. Heuland has favoured us withan authentic 
account of the mass of platinum deposited in the Royal Museum 
at Madrid. It is obviously the largest mass hitherto found. It 
weighs above a pound and three quarters.—(Annals of Philo- 
sophy, xii. 200.) 
I beg leave to call the attention of those manufacturers who 
have occasion for platinum vessels to the mode of purifying that 
metal proposed by the Marquis of Ridolphi, of which an account 
will be found in the Annals of Philosophy, xit.70. {t will not 
yield a pure metal, but [ think it hkely that it would answer suffi- 
ciently for all the purposes to which that metal is applied by 
manufacturers, and it would enable them to procure the metal at 
a much smaller price than can be at present charged for it, in 
consequence of the very expensive process by which it purified. 
If we can believe the accounts which have reached us from 
