2^3 Dr. Bi.agdrn’s Experiments on 
My fird objeft of invefligation was the ratio according to 
which equal additions of the fame fubftance deprefs the freez- 
ing point. I began with common fait ; and in order to avoid 
as much as poffible a fallacy in the experiments, becaufe the 
ordinary fait is never pure, and often not perfectly neutral, I 
chofe fome clean fait, in fair cryflals, which is fold in London 
under the name of Borrowflounnefs pure fait. This fait I 
diffolved in diddled water, in various proportions, and found 
the correfponding points of congelation to be as is expreffed in 
the annexed table ; where the fird column indicates the num- 
ber of parts and decimals of water to one part of the fait, and 
the fecond column (hews the freezing point found by the expe- 
riment. It appeared clearly, on comparing the proportions of 
water to fait, with the correfponding number of degrees which 
the freezing point was reduced below 3 2°, that the effedt of 
the fait was nearly in a fimple ratio ; namely, that if the ad- 
dition of a tenth part of fait to the water funk the freezing 
point about 11 degrees, or to 21 0 , it would be depreffed dou- 
ble that quantity, or to io° nearly, when a fifth part of fait 
■was diffolved in the water. To (hew, therefore, how far this 
limple proportion is exadf, I have added a third column to the 
table, which is made by feledting the lowed freezing point 
that was obtained without ambiguity in the experiment, and 
calculating, by a fimple inverfe proportion, what all the other 
points fhould have been according to that ratio. Thus when a 
fourth part of its weight of common fait was diffolved in wa- 
ter, I found the freezing point of the liquor to be 4 0 ; there- 
fore, to determine what it fhould be when only f- part of 
fait was added to the water, the formula is 32 : 4 :: 28 (the 
number of degrees that the point 4 0 is below the freezing 
point of pure water) : 3! ; which fubtra&ed from 32° gives 
2S 0 f 
