134 On ike Cknitractiorl which takes place in Mercury 



while cold, or assisted by the steam when it tjecomes hot, 

 it is instantly condensed into an impalpable powder, pos- 

 sessing all the qualities of calomel in its most perfect state. 

 The calomel, when thus prepared, is purer, whiter, and 

 more attenuated, than that obtained by grinding. It is 

 proper to wash the product over with water, before it is 

 dried, to rid it of any coarser particles which n^ay forip 

 about the mouth of the crucible. 



XXVIII. On the Contraction which takes place in Merciiry 

 at low Temperatures by, Ahstrcctlon of Heat ; — and on the 

 JRatio of Contraction between Mercury, Alcohol, Water^ 

 and Silver. By John Biddle, Esq, of Birmingham, 



Birmingham!!, Fp]t)ruary, 1808. 



To Mr, TiMoch, 



SIR, 



-^ LETTER frorri M. Tardy de la Brossy, dated Joyeuse, 

 (Ardeche) October 13th, 1805, addressed to Professor Pictet, 

 of Geneva, has appeared in your M.'^gazine [vol.xxiv. p. 322] . 

 It contains observations on some experirncnts which I had the 

 pleasure of showing to the Philosophical Society here on the 

 specific gravity of mercury in its frozen state, which experi- 

 inents were communicated to. the public through the me- 

 dium of Mr. Nicholson's Journal for April 1805. The 

 observations of M. Tardy de la Brassy have induced me tp 

 look over the original papers, containing the results of 

 those experiments, with som^. atUntion; and, with deference 

 to the opinions of that gentleman (though I fc^ar spme in- 

 accuracy exists), I must, in defence of my experiments ge- 

 nerally, and the deductions piade from them, request you 

 to commvmicate a fe\v experiments and olpservations through 

 the channel of your Magazine. 



M. Tardy dc la Brossy, after a^vowing tb^ object of his 

 communication to be *' the extension of truth, and the re- 

 moval of error,**, proceeds to describe the result of some of 

 mv former experiments, and to make his obscpvations on 

 iny calculations trom them, to which I wpuld refer; but if 



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