Wim 
166 - Mr. Kirwan’s ‘Rites’ on 
VENDISH abterveas: ‘that mercury, ‘fouled’ by thecaddition’ of : 
<¢ Jead or tin, depofits a powder whicli confifts in great Meafure> 
“© of the calx of the'metal : he: found alfo, that fome powder of 
this fort contained fixed air ; ‘but it is not clear that ‘this air’ 
«6 was! ‘ptoduced by the phlogiftication ofthe air in which the: 
cer} ifiercury was fhaken,‘as’ ‘the ‘powder was not prepared’ on? 
‘¢ purpofe, but was formed from mercury fouled by having» 
‘© bécn-ufed for various purpofes, and may therefore contain’ 
<s other impurities, -befides the metallic calx.” On this I re+) 
mark, that Dr. Prigstiey did ‘not indeed at firft prepare this: 
powder on purpofe; but he afterwards did fo prepare it (4Prizsr,) . 
p- 148, 149.) and obtained a powder exaétly of the fame fort; and: 
it is certain that the fixed air found in it proceeded from the» 
common air, both becaufe mictallic calces, not formed by amal~. 
gamation, will not unite with mercury, as is well known 3 .ands 
becaufe ‘this calx cannot be formed by agitation of the mercury; 
and lead, in phlogifticated, inflammable, or any other air'whichs 
is not refpirable; and the fixed air cannot proceed from:any 
impurity, as mercury will not unite in its running form to any: 
other but metallic fubftances, which it always’partially dephlo-; 
gifticates, like other: menftruums (3 Chy. Dijon, 425.). 
Of the Diminution of Refpirable Air by Combuftion, =~ 
Though I have no doubt but the diminution of refpirable air, 
by the combuftion of fulphur and phofphorus, proceeds alfo in 
great meafure from the produ€tion~and abforption of fixed air, 
yet I avoided mentioning this operation, as the prefence offa 
ftronger acid renders the prefence, of a weaker impoffible. to be, 
proved, more efpecially; ag: both. thefe acids precipitate lime , 
from lime-water; but the great increafe of weight which the 
3 phof- 
