— 305 — 



•hold of the investigation of the action of minute quan- 

 titles of organic matter on the human system; but 

 there is good reason to believe that future researches, 

 while developing the characters, composition, proper- 

 ties, and action of putrescible matter, will also shew 

 the differences on which the difference of result de- 

 pends, and will enable us to speak with greater cer- 

 tainty on this subject. 



Huving by these preliminary remarks to some extent 

 elucidated the nature of the emanations from putres- 

 rent matters, and their probable action on the human 

 system, I proceed to examine the action of charcoal, in 

 arresting putrefaction, in preventing the extrication of 

 offensive and noxious emanations, and thus conducing 

 mrtst powerfully to the purification of the atmosphere 

 of towns. 



It has long since been ascertained that porous subs- 

 tances ia general, whose pores are not too large, pos- 

 sess the property of condensing within their pores a 

 greater or smaller proportion of all gases, and in many 

 ca^es of effecting chemical combinations and decompo- 

 sition. Saussure, whose experiments have thrown so 

 mi'.ch light on A'egetable physiology, investigated this 

 subject with great caro and exactitude ; and other che- 

 mists of high repute have subsequently pursued these 

 researches. 



Tlie most powerful of these porous substances is the 

 metal platinum, which in certain conditions of its sur- 

 face, eviltntly connected with porosity, is capable of 

 causing the instantaneous combination of oxygen with 

 hydrogen, with the usual evoluiion of light and heat. 

 Al'hough the anpart^nt'y smooth surface of a wire or 

 pliile of pletinum is capable, under certain conditions, 

 of Cifectiiig this combination, the power is vastly in- 

 ere: sed by division. Spongy platinum obtained by 

 boating the ammoniac chloride of this metal to redness, 

 po'-sesses this power in a much higher degree ; but the 

 hiij;h»"3t is obtained wlien the metal is reduced to an 

 almost unnalpable black powder usually called plati- 

 num black. Whence, we may ask, arises this peculiar 

 power, so evidently connected with the degree of divi- 

 sion ? — We have the answer in the researches of Doe- 



