354 Dr. el ag den’s Hiftory of 
and in the adtion of the frigorific mixtures, that I fhould 
fuppofe fpirit-thermometers will always be employed in future, 
whenever any thing of this kind is attempted. 
§ 7. It is not a little extraordinary, that fince the death of 
Profeflor braun, now near fifteen years ago, all attention to 
the congelation of mercury fhould in a manner be laid afide on 
the fpot where it was originally difcovered. A dead filence on 
the fubjedt feems to have prevailed at Peterfburgh till this pre- 
fent winter ; when Dr. mat. guthrie, f. r. s. Phylician to the 
Cadet Corps of Nobles, having heard the matter much can u 
vafTed during his late vifit here, refumed the confideration of it 
on his return to that metropolis. The only intelligence I have 
yet received of Dr. Guthrie’s experiments or conclufions, is con- 
tained in one of his letters to Dr. garthshore of this Society, 
who has obligingly favoured me with the following extradh 
44 Having found,” fays Dr. guthrie, 44 in my late journey 
44 to Britain, that it remained a matter of doubt, whether mer- 
44 cury in its pure flate, unmixed with heterogeneous matter, 
44 had ever been or was capable of being congealed ; I am glad 
44 to be able, from the refult of feveral experiments, to inform 
44 you, that the purefl mercury known to the chemifts is capa- 
44 ble of congelation, and in that ftate will bear the hammer. 
44 I have done fomething alfo toward determining the point of 
44 its congelation, by determining what it is not, viz, 150° of 
44 Reaumur’s thermometer. 
44 A fine thermometer, made by nairne, graduated 150° 
44 of reaumur, that is, 337 0 of Fahrenheit below the 
44 freezing point” [or -305 0 ] 44 funk entirely into the bulb, 
44 while the mercury in which it was plunged remained per- 
44 fedlly liquid, nay had not as yet grown thick and gritty, a 
“ phenomenon 
