and 'attractive Powers of various f aline S ubjlances. 9 
tibn of the lighter ingredient. -This Increafe of denfity mnft 
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 mud: 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 un- 
deceived. 
* 
■ I muff alfo premife, that the abfolute weights of many forts 
of air have been accurately determined by Mr. fontana, at 
whofe experiments I was prefent, the thermometer being at 55% 
and. the barometer at 29 1 inches, or nearly fo. Their weights 
were as follows : 
Cubic inch, of common air 
°, 3 8 5 
Fixed air 
* 0,570 
Marine air 
0,654 
Nitrous air 
0,399 
Vitriolic air 
1 
O 
-<r 
CO 
Alkaline air - 
-0,2 
Inflammable, air * 
0,03 
OF 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 
~Tiquor in all refpecls 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. LX XL C this 
1 
