418 PHILOSOPHICAL TRANSACTIONS. [ANNO 1783. 



common on changing the mixtures ; but after waiting a considerable time, with- 

 out its descending again, he recollected Professor Braun mentioning that his 

 thermometers were always broken when below 600°. This made Mr. H. exa- 

 mine his, when he found the bulb was broken and fallen off; but on a diligent 

 search in the mixture, he could not find either quicksilver or the pieces of glass; 

 he therefore concluded it had dropped ofF into the other mixture, which un- 

 luckily he had thrown away the moment before, having occasion to use the bason 

 in decanting the present mixture : he had no doubt but it broke at the time the 

 quicksilver fell so rapidly. During the course of this experiment Mr. H. put 

 the apparatus g into the freezing mixture ; in a minute's time the quicksilver in 

 the inclosed thermometer had subsided into the bulb, and remained so during 

 the time it continued immersed in the freezing mixture, which was about a of 

 an hour ; but though the thermometer, which made part of the apparatus, 

 showed so great a degree of cold, yet the quicksilver in the cylinder was never 

 frozen ; and indeed the spirit thermometers, suspended in the mixture, seemed 

 to indicate, that there was not sufficient cold to freeze quicksilver, except at the 

 beginning ; for it is not effected at 40°, without continuing some time at that 

 degree, as appears very clearly from the 3d experiment. 



The 8th experiment was made Dec. 21, 1781, with a view to try whether 

 quicksilver would freeze while in contact with the freezing mixture. For this 

 purpose Mr. H. did not use the apparatus employed in the other examples, but 

 substituted another, by taking a gallipot made of flint stone (being thinner than 

 the common sort) of about an ounce measure, and filled it half full of quick- 

 silver, into which he inserted the mercurial thermometer b, and employed the 

 other mercurial thermometer A as an index, as before. Mr. H. hoped by this 

 means to determine exactly when the quicksilver was congealed, as he had free 

 access to it at all times, which was not the case when inclosed in the cylindrical 

 glass, the worsted wound round the tube of the ivory thermometer to exclude 

 the air, equally excluding any instrument from being introduced to touch the 

 quicksilver. He made a kind of skewer, with a flat point, of dried cedar wood 

 for lightness, which he found would remain in the gelatinous freezing mixture at 

 any depth ; but when inserted into the quicksilver contained in the gallipot, the 

 great disproportion of gravity made it rebound upwards, and by the touch he 

 could easily perceive, by the resistance it met with, whether it proceeded from 

 quicksilver in a fluid or congealed state. The event did not answer his wishes, 

 for he could not find that the quicksilver was frozen in the least during the trial. 

 Indeed the temperature of the air was not favourable, being under 20° below 

 the cypher. The large quantity too of the quicksilver in the gallipot, as well as 

 the thickness of that vessel, might both of them contribute to render the opera- 

 tion unsuccessful ; yet, as the apparatus thermometer showed the same degree 



