Royal Society of London. 363 
ing litharge, it causes a white precipitate in the liquor which 
soon falls to the bottom of the vessel. 
The same acid poured upon unadulterated wine merely 
brightens its colour a little, without producing any precipi- 
tate. 
This method, although a good one, is not so accurate as 
the employment of water charged with sulphuretted hy- 
drogen. 
In order to prepare this water, it is only necessary to put 
into a phial a paste made of iron filings and sulphur ; pouring 
afterwards into it some drops of sulphuric acid, and libe- 
rating the gas which is produced from the mixture into a 
flask filled with water, by, means of a bent tube with which 
the phial is furnished. 
Poured upon unadulterated wine, this water does not oc- 
casion the least change in it; while, on the other hand, it 
renders the wine Saulterated with litharge black and flaky, 
and produces an abundant precipitate, which soon falls to 
the bottom of the vessel. . 
Some people make use of sulphur or alkaline sulphurets ; 
but these re-agents produce in pure as well as in adulterated 
wine a change of colour, and precipitates so little distinct 
from each other, that it is difficult to establish any thing 
decisive from their differences. It will be much better to 
adhere to the processes here pointed out. 
LV. Proceedings of Learned Societies. 
ROYAL SOCIETY OF LONDON, 
Jasuany 8, 1807. The Right Hon. Sir Joseph Banks, bart. 
president, being recovered from his indisposition, took the 
chair, when an interesting mathematical paper was read on 
the power of friction and the resistance of bodies, applied to’ 
the cogs of wheels, &c., by Davis Giddy, esq. M.P. The 
principles, which were here slightly introduced in the form 
‘ofa letter at the request of the president, Mr. Giddy ob- 
served had been discovered nearly at the same time by the 
mathe- 
