and attraBlve Powers of various f aline Subjlances. p 
tion of the lighter ingredient. This increafe of denfity muff 
then arife from a clofer union of the component parts to each 
other than either had feparately with its own integrant parts 
and this more intimate union muft proceed from the attraction 
or affinity of thefe parts to each other : I therefore imagined 
this attraction might be eftimated by the increafe of denfity or 
fpecific gravity and was proportionable to it, but was foon ui> 
deceived. 
I muft alfo premile, that the abfolute weights of many forts 
of air have been accurately determined by Mr. fontana, at 
whofe experiments ! wasprefent, the thermometer being at 55^, 
and the barometer at 2p| inches, or nearly fa. Their weights 
were as follows : 
Cubic inch of common air 
Fixed air 
Marine air 
Nitrous air 
Vitriolic air 
Alkaline air 
Inflammable air 
0,385 
°o7° 
0,654 
0,399 
0,778 
0,2 
°,°3 
O F SPIRIT OF SALT. 
From the time I firft read in Dr. Priestley’s Experiments 
on Air (that inexhauftible fource of future difcoveries) of the 
exhibition of marine acid in. the form of air, free from wa- 
ter ; and that this air, reunited with water, formed an acid 
liquor in all rcfpefts the fame as common fpirit of fait ; I con- 
ceived the poffibility of. difcovering the exact quantity of acid 
in fpirit of fait of any given fpecific gravity, and by means of 
Vol. LXXI. C this 
