VOL. LII.] PHILOSOPHICAL TRAJSTSACTIONS. 551 



ing the contrary has been given out by some, that these chymical oils mixed with 

 the most highly rectified spirit of wine, produce no cold, either on their mixture 

 or half an hour after. 



It results from these experiments, that though there are many liquids which 

 can produce artifical cold, the nitrous acid is the most powerful ; and mercury 

 may be congealed by it, without any difficult process, at any time, when the heat 

 of the atmosphere is not greater than 175 by the thermometer before-mentioned. 

 And these experiments have not only succeeded with our author, but with many 

 others ; among whom, it may be sufficient to mention Messieurs Lomonosow, 

 Zeiher, Aepinus, and Model, as these gentlemen have made themselves well 

 known in the philosophical world. The nitrous acid was poured on the snow in 

 no determinate quantity ; sometimes a few drops were sufficient, sometimes it 

 required a larger quantity. Snow seems to be more fit for these experiments 

 than pounded ice ; as the former, from its loose texture, is of more apt and easy 

 solution. 



Hence it appears, that mercury is no longer to be ranked with the semi-metals, 

 but as a perfect one, fusible, though with a much less degree of heat than any of 

 the others. It agrees likewise with other metals ; as their parts like it, when in 

 fusion, attract one another, and run into globules, and, from a state of fluidity, 

 pass into a solid state, not all at once, but successively, and vice versa. But it is 

 worth inquiring, whether this metal, which agrees with all others, both in a solid 

 and fluid state, has not the particular property of boiling at a certain degree of 

 heat, which is by no means to be observed in other metals. The degree of heat, 

 in which mercury begins to boil, is not at 600 of Fahrenheit's scale, as is generally 

 imagined ; but at least at 709 of the same scale, which corresponds with 414 of 

 our author's, whose cypher is at the heat of boiling water. Both the boiling and 

 freezing of mercury have this in common ; that when it begins to boil, it rises 

 with rapidity ; and descends rapidly, when it begins to freeze. If therefore the 

 mean term of the congealation of mercury is fixed at 650 below the cypher, and 

 the term of its boiling at 4 1 4 above the cypher ; its greatest contraction to its 

 greatest dilatation, will be 1064 degrees of our author's thermometer, and 1237 of 

 Fahrenheit's ; as 212 is the point of boiling water in this last, and 32 the freezing 

 one ; which corresponds with 1 50, under the term of boiling water, in our 

 author's. Hence every one will see the great alteration of specific gravity in 

 frozen and boiling mercury, as, between one and the other, the 10th part of the 

 volume is lessened. 



It may be asked, why the mixture of snow and nitrous acid does not run into 

 a solid mass, and form itself into ice, but remain of a soft consistence, though 

 actually much colder than what is required to freeze aquafortis ? We have al- 

 ready mentioned that aquafortis freezes at 204 of our author's thermometer, which 



