(Papesies'- 
Mr. CAVENDISH’ S Aafwer, &e. I7r 
fure mild. This mildnefs of the alkali Mr. Kirwan accounts 
for by fuppofing, that the inflammable air; ‘which is ‘fepatated 
during the folution, and caufes the effervefcence, unites to the 
atmofpheric air contiguous to it, and thereby generates fixed 
air, which is abforbed by the alkali. But, in reality, the only 
circumftance from which Mr. pe Lassone judged the alkali to 
become mild, was its making fome effervefcence when faturated 
with acids; and this effervefcence is more likely to have pro- 
ceeded from the expulfion of inflammable air than of fixed air, 
as it feems likely, that the zinc might be more completely” 
deprived of its phlogifton by the acid than by the alkali. 
In the abovementioned paper I fay, Dr. Priesriey ob- 
ferved, that quickfilver fouled by the addition of lead or tin, 
depofits a powder by agitation and expofure to the air, which 
confifts in great meafure of the calx of the imperfect metal. . 
He found too fome powder of this kind to contain fixed air; 
but it muft be obferved, that the powder ufed in this _experi- 
ment was not prepared on purpofe, but was procured from 
quickfilver fouled by having been ufed in various experiments, 
and may therefore have contained other impurities befides the 
metallic calces. On this Mr. Kirwan remarks, that Dr. 
PrigsTLey did not at firft prepare this powder on purpofe, but 
he afterwards did fo prepare it (4 Pr. ‘p. 148. and 149.), and 
obtained a powder exactly of the fame fort. It was natural to 
fuppofe from this remark, that Dr. PriesrLey muft have ob- 
tained fixed air from the powder prepared on purpofe, and that 
I had overlooked the paflage ; ; but, on turning ‘to the pages re- 
ferred to, I was furprifed to find that it was otherwife, and 
that Dr. PriestLey not fo much’ as hints that he poanes 
fixed air from the powder thus prepared. 
Z 2 oe With 
