VOL. LXXIII."] PHILOSOPHICAL TRANSACTIONS. 427 



should have frozen ; the only thing extraordinary is, that the quicksilver in the 

 cylinder should have borne that cold without freezing. The same phenomenon 

 occurred in the 6th and 7th experiments, on putting the same apparatus into the 

 freezing mixture. 



In the 4 th experiment the ivory thermometer sank quickly to — 42° ; but soon 

 after rose half a degree, probably from the cold of the mixture diminishing ; it 

 then, after having remained 6 or 7 minutes at those two points, sank very quick to 



— 77°. It does not appear at what time the quicksilver in the cylinder began 

 to freeze, as it was not examined till long after the thermometer had sunk to 



— 77°, when it was found solid; but from the resemblance of this to the three 

 former experiments, it is most likely, that it did not begin to freeze till after the 

 thermometer had sank to — 77°. In the 5th experiment the wooden thermo- 

 meter was partly frozen before it was put into the freezing mixture, and the 

 ivory one was at — 40°. On putting them into the mixture, they both rose ; 

 the latter, half a degree ; the former, many degrees ; which shows that the 

 part of the mixture in which they were placed was rather warmer than the freez- 

 ing point, though that in which the spirit thermometer was placed was colder. 



Though in the 6th experiment the thermometer in the apparatus g froze with- 

 out the quicksilver with which it was surrounded freezing, yet in trying the 

 apparatus f in the same mixture, this did not happen ; but, on the contrary, it 

 afforded as striking a proof that the point of freezing quicksilver answers to 

 about — 40° on this thermometer as any of Mr. Hutchins's experiments ; for, on 

 taking out the apparatus after it had been 2 minutes in the mixture, the quick- 

 silver in the cylinder was found frozen solid, the inclosed thermometer standing 

 at 40° or 41° below O. After having been exposed for near an hour to the air, 

 which was then very little above the point of freezing quicksilver, only a small 

 quantity of the surface was become fluid ; the rest formed a frozen globe round 

 the ball of the thermometer, resembling polished silver, and in 17 m after this 

 only a segment of a globe of frozen quicksilver, with a concavity on the inside, 

 formed by the ball of the thermometer, was observed, the thermometer all this 

 while continuing the same as before, namely, at 40° or 41° below O ; so that in 

 this experiment the ball of the thermometer was surrounded for more than an 

 hour with quicksilver, which was visibly frozen and slowly melting, and during 

 all which time it continued stationary at 40° or 41° below O. 



Though the foregoing experiments leave no reasonable room to doubt that 

 this is the true point at which quicksilver freezes, yet Mr. Hutchins has, if 

 possible, made this still more evident by his last 2 experiments ; as, in the first 

 of them, he froze some quicksilver in a gallipot immersed in a freezing mixture, 

 so that the quicksilver was in contact with, and covered by, the snow and spirit of 

 nitre ; and in the latter in the open air, by the natural cold of the weather, and 



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