on the Specific Gravities , &c. of Saline Subjfances. i 
inflammable air, from metals which is the pureft of all, is 
alio the molt inflammable. 
Secondly, Inflammable air is alfo the principle which reduces 
metallic earths to a metallic {late, and gives them their metal- 
lic fplendor. This has been proved analytically and fyntheti- 
cally, and therefore may be laid to be as completely demon- 
ftrated as any thing in natural philofophy : thus Dr. priest- 
ley has extracted inflammable air from iron and zinc by heat 
alone ; and the iron, thus {tripped of its phlogifton, loft its 
fplendor, and was of a black colour, which is that which iron, 
{lightly dephlogifticated, always afl'umes, as appears by martial 
athiops: fo alfo zinc and regulus of arlenic, when once in- 
flamed, lofe their metallic appearance : fo alfo a mixture of 
lead and tin inflames in a moderate heat, and then both are 
converted into a calx deftitute of fplendor and malleability. 
On the other hand, if a current of inflammable air, in the abt of 
combuftion, be direbted on the calces of iron, lead, or mercury, 
they are immediately revived and reftored to their metallic 
form, as appears by the experiment of Mr. chaussier *. The 
following experiment is {fill more conclufive : if a polifhed 
plate of iron be put into a faturate and dilute folution of copper 
in the vitriolic or marine acids (I mention thefe becaufe they 
are commonly ufed for the produ&ion of inflammable air, 
though the refult is the lame when other acids are ufed), no 
effervefcence will arife, no- inflammable air will be caught ; but 
the iron will be diflolved, and the copper precipitated in its 
metallic form. Here inflammable air muft be produced as 
ufual, for the acid quits the copper and.diflolves the iron ; but 
"\ this inflammable air inftantly lofes its aerial form, and unites- 
to the copper, juft as fixed air leaves alkalies to unite to lime 
* 10 Roz. 313. 
without. 
