f 33 6 ] 
faline folutions will not cryftallize without much 
difficulty in an exhaufted receiver j perhaps becaufe 
the particles of fait cannot attract that principle which 
fhould cement them together, which at lead: may 
be feen efcaping from them when they begin to be 
feparated. Mr. Boyle obferved, that aquafortis, 
poured upon a ftrong vegetable alcali, did not cry- 
jflallize till it had been long expofed to the air (though 
I fhould rather attribute this failure to the weaknefs 
of his aquafortis than to the want of air, fince I have 
frequently, by ufing the fuming fpirit of nitre, obtain- 
ed crydals of an inch in length almoft inftantane- 
oufly) ; and feveral other phenomena might be ad- 
duced refpeding the cryftallization of falts, which 
feem to indicate the neceffity of admitting air as a 
very efficacious infcrument in producing that efFed : 
but future experience may tend to elucidate this 
matter. Having ufed great attention in making the 
experiments from which the preceding table was 
compofed; I thought I had a good opportunity of 
deriving from it the fpecific gravities of the falts 
which are there mentioned. I accordingly calculated 
the following table ; in the firft column of which 
are exprefied the fpecific gravities as calculated from 
the increafe of bulk before folution j in the fecond, 
after the folution. 
Genuine Glauber’s fait 
Crydals of kelp 
Volat. lalt of fal ammoniac 
Sal ammoniac 
Sugar refined, brown, barley 
White fugar candy 
1,380 1 ,6 1 1 
1,414 1,467 
1,45° 1,787 
1,450 1,487 
1,487 i,6ir 
G5 6 7 j ’ 611 
