102 PHILOSOPHICAL TRANSACTIONS. [aNNO 1780. 



accident, and to both acids having happened to be of that precise degree of heat 

 before the experiment began, that their heat after dilution should coincide with 

 the freezing point answering to their new strength. The true cause seems to 

 be as follows. It will be shown presently that the freezing point of these acids, 

 when diluted as in the foregoing experiments, is much less cold than when they 

 are considerably more diluted ; and it was before shown to be much less cold 

 than when not diluted ; so that there must be a certain degree of strength, not 

 very different from that to which these acids were reduced by dilution, at which 

 they freeze with a less degree of cold than when they are either stronger or 

 weaker. Now in these experiments, the temperature of the liquors before dilu- 

 tion was below this paint of easiest freezing, and a great deal of the acid was in 

 a state of congelation all the time of dilution ; the consequence of which is, 

 that when they were diluted to the strength of easiest freezing, they would also 

 be at the heat of easiest freezing ; for they could not be below that point, be- 

 cause, if they were, so much of the acid would immediately freeze as would 

 'raise them up to it ; and they could not be above it, for, if they were, so much 

 of the congealed acid would dissolve as would sink them down to it. After they 

 were arrived at this strength of easiest freezing, the addition of more snow 

 would produce cold, unless this strength be greater than that at which the addi- 

 tion of a small quantity of snow begins to produce cold ; but even were this the 

 case, heat would not be produced, but the temperature of the acids would re- 

 main stationary till they be so much diluted that the addition of more snow 

 should produce cold. So that, in either case, the heat of the acids, at the time 

 that the addition of fresh snow began to produce cold, must be that of easiest 

 freezing ; and consequently, as this heat was found to coincide very nearly with 

 the freezing point of these acids, after dilution, it follows that their strengths at 

 that time could differ very little from the strength of easiest freezing. If the 

 temperature of the liquors at the beginning of the experiment had been above 

 the point of easiest freezing, none of the acid would have congealed during the 

 dilution, and nothing could have been learnt from the experiment relating to the 

 point of easiest freezing ; but the heat would have kept increasing, till the acid 

 was diluted to that degree of strength at which the cold produced by the dis- 

 solving of the snow was just equal to the heat produced by the union of the 

 melted snow with the acid ; after which the addition of more snow would begin 

 to produce cold. 



In the dephlogisticated spirit of nitre the freezing points answering to the 

 strength of .434, .53, and .56, were said to be — 4^*4-, — 19°, and — 30°; 

 and the differences of — 30° and — 19° from — 4% are to each other very 

 nearly in the duplicate ratio of .126 and .096, the differences of the correspond- 

 ing strengths from .434 ; which, as .434 is the strength of easiest freezing, is 



