^ 



428 



PHILOSOPHICAL TRANSACTIONS. 



[anno 1788. 



Freezing point. I Difference. 



that the strength at which the acid freezes with Strength. 

 the least cold is .418, and that the freezing 

 point answering to that strength is — 2-p'/- 



In order to show more readily the freezing 

 point answering to any given strength, I have 

 computed, by the same method, the annexed 

 table, in which the strengths increase in arith- 

 metical progression. It was before shown that 

 the freezing points, found by the first method, 

 ought to be below those of the whole mass, and must in all probability be above 

 those of the decanted liquor. In order to see how this agrees with observation, 

 I computed in the above-mentioned manner the freezing points answering to the 

 strength of the whole mass, and compared them with the observed freezing 

 points. The result is given in the following table. 



It may be observed, that the freezing point of N° 7, tried in the first way, is 

 considerably above that corresponding to the strength of the whole mass ; but as 

 this experiment appears to be doubtful, and not unlikely to exceed the truth, we 

 may safely reject it as erroneous. All the others, as might be expected, are 

 lower than those corresponding to the strength of the whole mass, and above 

 those observed in the 2d manner, and therefore serve to confirm the truth of the 

 above determination of the freezing points of spirit of nitre ; and also show, that 

 in this acid the point of spirituous congelation is pretty regular, and does not de- 

 pend much, if at all, on the rapidity with which the congelation is performed. 



The point of aqueous congelation, however, seems liable to considerable irre- 

 gularity ; for N° J 3, after having been exposed to the cold, froze on agitation, 

 the congelation being of the aqueous kind, and the thermometer stood stationary 

 therein at — 34°. The ice being then almost melted, it was again exposed to the 

 cold, till a good deal was frozen ; but yet its temperature was then no lower than 

 — 324-°, though the quantity of frozen matter must certainly have been much 

 more than in the first trial. The fluid part being then decanted, and the frozen 



