

ON DUST AND DISEASE. 183 



certain gentle kinds of smoke, it was no match for the 

 pungent fumes of a resinous fire. For the purpose of 

 catching the atmospheric germs, M. Pouchet spread a 

 film of glycerine on a plate of glass, urged air against 

 the film, and examined the dust which stuck to it. 

 The moistening of the cotton-wool with glycerine was 

 a decided improvement ; still the respirator only 

 enabled us to remain in dense smoke for three or four 

 minutes, after which the irritation became unendurable. 

 Reflection suggested that, besides the smoke, there 

 must be numerous hydrocarbons produced, which, being 

 in a state of vapour, would be very imperfectly arrested 

 by the cotton-wool. These, in all probability, were 

 the cause of the residual irritation ; and if these could 

 be removed, a practically perfect respirator might 

 possibly be obtained. 



I state the reasoning exactly as it occurred to my 

 mind. Its result will be anticipated by many present. 

 All bodies possess the power of condensing, in a greater 

 or less degree, gases and vapours upon their surfaces, 

 and when the condensing body is very porous, or in a 

 fine state of division, the force of condensation may 

 produce very remarkable effects. Thus, a clean piece 

 of platinum- foil placed in a mixture of oxygen and 

 hydrogen so squeezes the gases together as to cause 

 them to combine ; and if the experiment be made with 

 care, the heat of combination may raise the platinum 

 to bright redness. The promptness of this action is 

 greatly augmented by reducing the platinum to a state 

 of fine division. A pellet of ' spongy platinum,' for 

 instance, plunged into a mixture of oxygen and hydro- 

 gen, causes the gases to explode instantly. In virtue 

 of its extreme porosity, a similar power is possessed by 

 charcoal. It is not strong enough to cause the oxygen 

 and hydrogen to combine like the spongy platinum, 



