PHILOSOPHICAL TRANSACTIONS. 



46l 



VOL. LXXVIII.] 



The numbers in the 3d column of the table come so near to those in the 2d, 

 that most likely the small differences between them ought to be ascribed to 

 errors in the experiments ; whence we should conclude, that the salt lowers the 

 freezing point in the simple inverse ratio of the proportion which the water bears 

 to it in the solution. This solution was in one instance cooled 84^, and in several 

 5 or 6°, below its freezing point; but in general it shot rather more readily than 

 some other solutions; which he ascribed, from the analogy of his former expe- 

 riments, to its less transparency. This salt with snow, in the manner of frigo- 

 rific mixtures, produced a cold of — 4°. 



Nitre. 



The next salt which was tried for its effect in lowering the freezing point of 



water, was nitre. It was part of a large compound Proportion j Freezing | Freezing 



crystal, or bundle of crystals, apparently very pure, 

 such as is used in manufacturing the best gun- 

 powder. This being mixed with distilled water, 

 in different proportions, the solutions froze ac- 

 cording to the annexed table. The 3d column is 

 calculated from the 5th experiment, in which th^ 

 freezing point of a solution of one part of salt in 

 eight of water proved to be 26°. 



of water to point by the 

 fexperiment. 



the salt. 



32 

 24 

 16 

 10 



1 



1 



1 



1 



8 : 1 

 7.9: 1 

 7: 1 



6.85 : 1 



30i° 



30 



28| 



27 



26 



point by cal- 

 culation. 



26i 

 27 



30^° 

 30 

 29 

 271 

 26 

 salt deposited, 

 salt deposited. 



{much salt 

 deposited. 

 Nitre is well known to differ from common salt in being much more soluble 

 in warm than in cold water. Hence it would be nothing remarkable, that the 

 solutions being made in water above the freezing point, some of the salt should, 

 when they exceeded a certain strength, be deposited before they began to freeze. 

 But a further question occurred here, whether, when a solution was cooled below 

 its freezing point, the salt would still continue to be deposited; or whether it 

 would not have parted with all the salt it was obliged to let go by the time it 

 came to the degree at which it was to freeze, and would retain the remainder 

 notwithstanding any subsequent cooling. To determine this. Dr. B. noticed 

 carefully the quantities of salt deposited at the bottom of the tumbler, in com- 

 parison with the cold of the solution as shown by the immersed thermometer; 

 and he found, that in some cases (for instance, when the salt was to the water 

 only as 1 : 10) the deposition did not begin till after the solution had passed its 

 freezing point; and that when it began earlier, still there was no stop at the 

 freezing point, but the quantity continued augmenting as the cold of the solution 

 proceeded, and that rather in an increasing ratio. Thus when the saturated so- 

 lution was cooled 8 or 10° below its freezing point, which often happened, the 

 collection of nitre at the bottom was very great; and in this manner he could 

 render a saturated solution of nitre no longer saturated when it came to freeze, 

 the deficiency being sometimes so great as to raise the point of congelation a 



