460 PHILOSOPHICAL TRANSACTIONS, [anNO 1788. 



of Congelation in Water. By Chas. Blagden, M.D., Sec. R.S. and F.A. S. 



p. '2^77- 



The experiments necessary to determine what effect the admixture of various 

 substances would produce on the property of water to be cooled below the freez- 

 ing point, naturally led to a more particular consideration of the power of such 

 admixtures in making water require a greater degree of cold before it congeals. 

 Many curious questions occurred on this subject, which could only be answered 

 by fresh experiments. These were made nearly in the same manner as the pre- 

 ceding; that is, the liquor, whose freezing point was meant to be tried, was put 

 into a glass tumbler, to the height of 2 or 3 inches above the bottom, and the 

 tumbler was then immersed in a frigorific mixture of common salt and ice or snow. 



The first object of investigation was the ratio according to which equal addi- 

 tions of the same substance depress the freezing point. Dr. B. began with com- 

 mon salt, of the purest kind. This salt he dissolved in distilled water, in various 

 proportions, and found the corresponding points of congelation to be as expressed 

 in the annexed table ; where the first column indicates the number of parts and 

 decimals of water to one part of the salt, and the 2d column shows the freezing 

 point found by the experiment. It appeared clearly, on comparing the propor- 

 tions of water to salt, with the corresponding number of degrees which the 

 freezing point was reduced below 32°, that the effect of the salt was nearly in a 

 simple ratio; namely, that if the addition of a 10th part of salt to the water 

 sunk the freezing point about 11°, or to 21°, it would be depressed double that 

 quantity, or to 10° nearly, when a 5 th part of salt was dissolved in the water. 

 To show therefore how far this simple proportion is exact, a third column is 

 added to the table, which is made by selecting the lowest freezing point that 

 was obtained without ambiguity in the experiment, and calculating, by a simple 

 inverse proportion, what all the other points should have been according to that 

 ratio. Thus, when a 4th part of its weight of common salt was dissolved in 

 water, the freezing point of the liquor was 4°; therefore, to determine what it 

 should be when only -gV part of salt was added to the water, the formula is 

 32 : 4 :: 28 (the number of degrees that the 

 point 4° is below the freezing point of pure 

 water): 3-1-; which subtracted from 32° gives 

 28°4- for the freezing point of that solution. 

 All the rest of the 3d column of the table 

 is found in the same manner, and with very 

 little trouble, because 4 X 28 = 1 1 2 is a 

 constant number, which being divided by the 

 numbers of the first column, the quotient is 

 the number of degrees sought. In all the expe- 

 riments, none but distilled water was employed. 



Common salt. 



