426 PHILOSOPHICAL TRANSACTIONS. [ANNO 1783. 



The 3d experiment was tried while the former was carrying on, and was made 

 by putting the other apparatus, namely, that with the thermometers g and b, 

 into the first mixture made for the former experiment, and which may conse- 

 quently be supposed to have lost great part of its cold. The ivory thermometer 

 quickly sank to — 43°, where it remained stationary for near 12 m . The appa- 

 ratus being then taken out to be examined, the quicksilver in the cylinder was 

 found fluid, but thick and in grains, like crumbs of bread. The apparatus 

 was then put back into the mixture ; and, on observing the thermometer, it 

 was found to have risen to — 40°, where it remained stationary about 40 m ; being 

 then examined, the quicksilver was found solid. 



It appears therefore, that the cold of the mixture was sufficient to cool the 

 quicksilver in the cylinder about 3° below the point of freezing, but did not 

 make it freeze till, on taking out the apparatus, the agitation suddenly set it 

 a freezing, and produced the appearance described by Mr. Hutchins. This 

 immediately made the inclosed thermometer rise ; so that when it was re-placed 

 in the mixture and observed, it stood exactly at the freezing point. It appeared 

 by the spirit thermometer, that the cold of the mixture, at the time the appa- 

 ratus was first taken out to be examined, was only 2° below the point of freez- 

 ing, which agrees very well with this explanation. This experiment therefore 

 affords a fresh confirmation that the point of mercurial congelation is — 40° on 

 these thermometers, and that quicksilver will bear being cooled a little below 

 that point without freezing. 



In the 4th, 5th, 6th, and 7th experiments a new phenomenon occurred, 

 namely, the ivory thermometer sank a great deal below the freezing point 

 without ever becoming stationary at — 40°. In the 5th experiment, tried with 

 the apparatus g, it quickly sank to — 42°, and then, without remaining 

 stationary at any point, sank in half a minute to — 72°, and soon after remained 

 fixed at — 79°. While it was at — 79°, the apparatus was twice examined, and 

 the quicksilver found fluid; but being again examined after having been removed 

 into a fresh mixture, it was found solid. It seems likely from hence, that the 

 quicksilver in the cylinder was quickly cooled so much below the freezing point 

 as to make that in the inclosed thermometer freeze, though it did not freeze 

 itself. If so, it accounts for the appearances perfectly well ; nor does there seem 

 any thing improbable in the explanation, except that it is contrary to what hap- 

 pened in the first 3 experiments; but the degree to which fluids will bear being 

 cooled below the freezing' point without freezing, seems to depend on such 

 minute circumstances, that Mr. C. thinks this forms no objection. It must be 

 observed, that the cold of the mixture appeared by the spirit thermometer to be 

 5 or 6 degrees below the freezing point ; so that if the quicksilver in the cylinder 

 was as cold as the mixture, it is not at all extraordinary that the thermometer 



