330 Dr. blagden’s Hijlory of 
mg to their fpecihc gravity, are thefe four: platina *, gold, 
quickfilver, and filver. 
In the general progrefs of fcience, it is always ufeful at 
intervals, and efpeciallv when any confiderable advance has been 
made, to look round and contemplate the profpeft left behind. 
Thus our adlual fituation is more diftinftly comprehended, and a 
better judgement may be formed of what remains to be done. 
For this reafon, I thought it might not be unacceptable to the 
Society, if I were, on the prefent occafion, to lay before them 
an account of the different obfervations and experiments I have 
been able to colledl, relative to the congelation of quickfilver; 
efpecially as many of thefe are recorded in books not eafily 
procured, and in languages little underflood by the learned 
of this country. I fhall begin with the various attempts 
which have been made to render this metal folid by frigorific 
mixtures, and then enumerate the many inffances in which 
that effedl has certainly been produced by the natural cold of 
the air. 
PART I. 
§ i. IT was undoubtedly M. Joseph ad am braun, Pro 
feflor of Philofophy in the Imperial Academy at Peterfburg, 
who firff, upon decifive evidence, eftablifhed the faff, that 
quickfilver can be made folid by a diminution of its heat : but, 
* Unlefs, indeed, the irreducible black powder, obtained by M. tillet> 
fhould be thought to place platma among the imperfeft metals. See Mem. dc 
l’Ac, Roy. des Scienc, 1779, p, 404, foe, 
7 as 
