and attractive Powers of various f aline Subfiances, 39 
From the weight of the aerial acid, in its fixed ftate, it hap- 
pens, that fixed alkalies, when united to it, are fpecifically 
heavier than when united either to the vitriolic or nitrous acids. 
Thus Mr. r. watson, in the Phil. Tranf. for the year 1770, 
p. 337. found the fpecific gravity of dry fait of tartar (including 
filiceous earth) to be 2,761 : whereas the fpecific gravity of tar- 
tar vitriolate was only 2,636, and that of nitre 1,933. The 
reafon why nitre is :fo much lighter than tartar vitriolate, is, be- 
caufe it contains much more water, and its union with the 
alkali is lefs intimate. 
Laftly, I have drawn up a table of the quantity of mild al- 
kali, containing 6,7 per cent, of earth (which is its ufual degree 
of purity) to he found in natural or artificial iolutions of this 
alkali, the thermometer at 63° ; and though it is not quite ac- 
curate, wanting about 1,1 per cent, of the truth, yet,. I pre- 
fume, it may be found ufeful, as this error- is eafily correfled. 
Table 
