100 PHILOSOPHICAL TRANSACTIONS. [aNNO 1785. 



served however, that the same diluted spirit, which at one time bore being cooled 

 to — 39°, at another froze, without any apparent cause, when its cold was .cer- 

 tainly less than — 30^, and most likely not much below — 18°. 



The freezing point differs remarkably, according to the strength of the acid. 

 In the diluted dephlogisticated and common spirit, the freezing point was — 5° 

 and — 1%. In the dephlogisticated and common spirit, the decanted parts 

 of which were stronger than the foregoing in scarcely so great a proportion as 

 that of 4 to 3, it seemed to be — 30° and — 31°4-. It may indeed be suspected, 

 that as this point was determined only by pouring a small quantity of the acid 

 into a glass, at a time when the air and glass were much colder than the acid, 

 these decanted liquors might be cooled by the air and glass, and so make the 

 freezing point appear lower than it really was : but I do not think this could be 

 the case ; for as the decanted liquors were full of small filaments of ice, they 

 could hardly be cooled sensibly below their freezing points without freezing ; and 

 any cold, communicated to them by the air or glass, would serve only to convert 

 more of them into ice, without sensibly increasing their cold : so that I think 

 this experiment determines the true freezing point of their decanted part ; but 

 it must be observed, that as the decanted part was rather stronger than the rest, 

 it is very possible that the freezing point of the undecanted part might be consi- 

 derably less cold. 



A circumstance which might incline one to think, that the way by which the 

 freezing point was determined in this experiment is defective, is, that the freezing 

 point of the dephlogisticated acid N° 27, though nearly of the same strength as 

 the last-mentioned, but rather stronger, was much less low, being only — 19°. 

 But I have little doubt that the true reason of this is, that in the former acid 

 the strength of the decanted part, which is the part whose freezing point was 

 tried, was found to be at least -^-V greater than that of the whole mass ; whereas 

 in N° 27 the fluid part was in all probability not sensibly stronger than the whole 

 mass ; for as N° 27 was cooled only 7° below the freezing point, and its tempe- 

 rature was tried soon after its beginning to freeze, not much of the acid could 

 have frozen ; whereas the other was cooled 1 5° below its freezing point, and 

 was exposed for an hour or two to an air not much less cold, in consequence of 

 which a considerable part of the acid must have frozen ; so that in all probability 

 the acid, whose freezing point was found to be — 30°, was in reality -5V part 

 stronger than that whose freezing point was — 19°. 



If this reasoning be just, the freezing point of these acids is as follows : 



-[ 



Freezing point. 

 .56 - 30° 



Dephlogisticated spirit of nitre, whose strengt= < 53 — 19 



A37 - H 



c 54. 3ii 



Conunon spirit of nitre, whose strength = < ^, j __ j | 



