294 Blag den’s Experiments on 
any peculiar effeCt on the freezing point. But having made 
the experiment with nearly a faturated folation of borax, the 
thermometer when it congealed was evidently below 32 0 : I 
believe about a degree. 
As a neutral or middle fait, which when crydallized is al- 
ways nearly of the fame nature, anddiffolves in a regular pro- 
portion in water, feemed likely to afford the mod: fimple cafe 
of the effect of extraneous admixtures, it was with fuch that 
1 began thefe experiments. But having found that with them 
the fimple ratio prevailed, I proceeded to try fublfances of a 
more variable nature, and capable of being mixed with water 
in almod any proportion ; fuch as acids, alkalies, and ardent 
fpirits. A material difference in the law, which feemed to 
occur in thefe new experiments, renders it proper to defer the 
account of them till fome reflections on the preceding fa£ts, 
with a few additional experiments to which they gave rife, 
have been premifed. 
It is now, I believe, univerfally allowed, that in frigorific 
mixtures the melting of the fnow or ice is the principal caufe 
of the cold produced ; all that heat which mud become latent 
in order to give water its fluid form being taken from the fen- 
iible heat of the ingredients. But as, when crydallized falts 
are employed for the purpofe, thefe alfo are reduced to a liquid 
form, there mud, from this circumdance, be fome additional 
cold produced, fuch for indance as would be occafioned by dif- 
folving the fame fait in water. Suppofe then that the latent 
heat of water is 1 50 degrees, and that fal ammoniac, in diflolving 
to faturation, produces fo much cold as finks the whole folution 
about 20 0 ; it is evident, that if this fait and ice are mixed 
together in fuch proportions as judto melt one another, the total 
cold generated in the operation mud amount to 170 degrees. 
2 And 
