ON THE EFFECTS OF URBAN FOG UPON CULTIVATED PLANTS. 55 



of coal-combustion with which it may be contaminated, as in 

 foggy weather. 



Charcoal undoubtedly possesses remarkable properties as an 

 absorbent, and Mr. Toope is by no means the first to call attention 

 to its properties in this respect. Forty years ago the chemist 

 Stenhouse* made observations on these properties, and it may not 

 be without interest to call attention to what he said about it. In 

 the paper referred to, Stenhouse describes and illustrates the 

 remarkable property of charcoal as an absorbent and oxidiser of 

 the products of decomposition of organic matter. He describes 

 how the carcases of dogs were kept covered with a thin layer of 

 powdered charcoal — but otherwise exposed — without any nuisance 

 arising therefrom. He adds that he has devised a respirator 

 on this principle, to be used in districts smitten with cholera or 

 yellow fever. He found, further, that with such a respirator 

 he could breathe with impunity air containing large amounts 

 of ammonia, sulphuretted hydrogen, and other hurtful gases. 

 Finally, he suggested the application of charcoal for purifying the 

 air of houses located in infected districts — all air admitted to be 

 passed through thin canvas bags containing crushed charcoal. 

 Were such precautions taken, many regions at that time fatal to 

 Europeans could be, he was sanguine, dwelt in with impunity. 



In a later papert Stenhouse describes his experiments, show- 

 ing how the absorbent property of charcoal could be greatly 

 increased. From this paper I venture to make the following 

 extract, as charcoal seems to have fallen into desuetude as an 

 absorbent : — 



" The lighter kinds of wood charcoal, owing to the nine 

 volumes of oxygen gas contained in their pores, possess a con- 

 siderable power of oxidising the greater number of easily alterable 

 gases and vapours. The absorbent power of charcoal is com- 

 paratively much greater than its capacity for inducing chemical 

 combination. In this respect charcoal presents a remarkable 

 contrast to spongy platinum, which, though inferior as an 

 absorbent for some gaseous substances — such, for instance, as 



* J. Stenhouse," Ueb. die entfiirbenden und disinficirenden Eigenschaften 

 der Holzkohle, nebst Beschreibung eines Kohlen-Kespirators zur Keinigung 

 der Luft durch Filtration,'' Annalcn der Chcmie und Pharmacie, Bd. xc. 

 1854, p. 18G. 



t J. Stenhouse, " On Platinised Charcoal," Journ. Chcm. Soc. viii. 1856, 

 p. 105. 



