174 TEST FOR ARSENIC. 



result ; and this rapidity will be prodigiously increased by keep* 

 and probably ing off the surrounding pressure, as in Professor Leslie's expe- 

 to'the's' "^ rirnent - Whether there be any practical limit of temperature, 

 limit. below which these or all volatile or fluid bodies could be pre- 



vented from assuming the gaseous state, is, I think, beyond the 

 reach of our inquiries. 



Freezing pro- These cursory remarks upon cooling 1 processes, may lead us 



cesses may be ... , - . . -- rT . 



improved by to infer, in the way of conjecture, that Mr. Hutton s process 



discovery or may consist in the discovery or use of one of the most powerful 

 selection of a . . . . . . a r iU 



freezing mix- freezing mixtures, and preventing the influence oi the sur- 



ture, and rounding heat by a judicious application of the means similar to 

 theexiraneons lnose pursued by Walker ; — or, much rather, that instead of 

 heat, this last, he may have applied Professor Leslie's process as to 



ker's^o/ Les" tue externa ^ cooling, by evaporation of ether in vacuo, to a 

 lie's method, vessel containing his freezing mixture. The apparatus for 

 doing this, or for effecting his purpose otherwise, would de- 

 mand a display of skill which we may reasonably expect will 

 add to the philosophical reputation of Mr. Hutton. 



III. 



Some Remarks on the Use of Nitrate of Silver, for the Detec- 

 tion of minute Portions of Arsenic, By Alex. Marcet, 

 M. D. F. R. S.* 



Test fo de- TT^ tne interesting account of the poisonous effects of arsenic, 



tecting arse- JL presented to the Society by Dr. Roget, and published in the 



nic; viz solu- stconc i volume of the Medico-Chirurgical Transactions!, the 



tions of ammo- . . 



nia, and of ni- author has recommended, for the detection of this poison, a 



**£?& .f r * test which I pointed out to him, and which, from a variety of 

 added by alte- r , , . , , . , . J . 



ations. experiments, which we tried together, with a view to ascertain 



"• Read to the Medical and Chirurgical Society of London, in De- 

 cember last, and by them published. It is here inserted, not only on 

 account of its intrinsic value, but because it bears reference to Mr. 

 Sylvester's paper in our thirty-third volume. — N. 



f I take this opportunity of stating, at Dr. Roget's request, that 

 the patient, whose case he there related, completely recovered her 

 health, and has remained well ever since. 



its 



