296 Dr. Blag£)En’s Experiments on 
According to this explanation, the greateft cold to be pro- 
duced .with any fait and ice or fnow fhould be that with which 
a faturated lolution of the fame fait freezes; which was for- 
merly eftablffhed by M. De Luc as a fa< 5 t, and is in general 
conformable to the preceding experiments. Thus, when a 
folution of one part of fal ammoniac in four parts of water was 
put into the frigorific mixture, lome of the fait was depofited, 
and then the folution on freezing railed the thermometer to 4 0 , 
which is exadfly the cold produced by a mixture of the fame 
fait with fnow. Likewife the ftronger folutions of nitre had 
their freezing point between 26° and 27 0 ; thofe of green 
vitriol near 28° 3 and fo of moft of the other falts, correfpond- 
ing with the cold of their frigorific mixtures. This agree- 
' 
ment, however, is liable to be modified by feveral circum- 
ftances. For in fiance, if the fait be of that nature that more 
of it is held in folution in warm than in cold water, it becomes 
extremely difficult to have the folution, at the moment iu 
freezes, exactly loaded with that quantity of fait which is moll: 
advantageous for acting upon the ice or fnow. Too much may 
have been depofited by the cooling previous to the congela- 
tion ; or fome refinance having occurred to the cryftallization 
of the fait, more of it may be retained at the moment of 
congelation than properly belongs to the folution at that tem- 
perature. The purity of the falts likewife, their particular na- 
ture as inclined to deliquefce or to fall down in powder in the 
air, the rapidity of their adlion upon the ice or fnow, mull: 
neceffarily be taken into the account, as influencing the degree 
of cold they can produce. 
It is an evident corollary from the above-mentioned agree- 
ment, that if the freezing point of the folution of a fait in 
water in any known proportion be given, its degree of folubi- 
lity 
