extracted from different Kinds of Waters. 449 
periments made upon each of thofe quantities of air 
treated after my method with the nitrous air. The air 
of the ftreet gave II- 13 , 11 + 6; the air of the ftone gal- 
lery, which was 202 feet high, gave II- 14, 11 + 5 ; and 
the air of the iron gallery, which was 313 feet high, gave 
II- 14, II + s. The refults of the two laft experiments 
are exadtly the fame ; and that of the firft is hardly at 
all different from them. Mr. cavallo, who has Ihewn 
the literary world his ability in examining nature, af- 
lifted me in thofe experiments, fo that a miftake 
can hardly be fufpedfed. From this we clearly fee, 
how little the experiments hitherto publifhed, about 
the differences of common air, are to be depended 
upon . In general I find, that the air changes from one 
time to another; fo that the differences between them 
are far greater than thofe of the airs of different coun- 
tries, or different heights; for inftance, I have found that 
the air of London, in the months of September, Octo- 
ber, and November, 1778, when treated with the ni- 
trous air, gave 11-6, 11+ 15, which is a mean refult 
of many experiments which differed very little from 
each other. The 26th day of November lalf, I found 
the air for the firft time much better, for it gave II- 1 2, 
11+ 1 2; but the 14th of February laft, the air gave 
II- 1 8, 
