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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



ammonia, of which spongy platinum absorbs only thirty volumes, 

 while charcoal absorbs ninety — is, nevertheless, immenselymore 

 effective both as an oxidiser and as a promoter of chemical com- 

 bination generally. As it is desirable for some purposes, while 

 retaining the absorbent power of charcoal unimpaired, to increase 

 its oxidating influences, it struck me that this important object 

 might be easily effected by combining the charcoal with minutely 

 divided platinum. In this way a combination is produced to 

 which I have given the name of platinised charcoal, which 

 possesses the good properties of both of its constituents. In 

 order to platinise charcoal, nothing more is necessary than to 

 boil the charcoal, either in coarse powder or in large pieces, in a 

 solution of bichloride of platinum, and when the charcoal has 

 become thoroughly impregnated with the platinum, which seldom 

 requires more than ten minutes or a quarter of an hour, to heat 

 it to redness in a close vessel — a capacious platinum crucible being 

 very well adapted for this purpose. When 150 grains of charcoal 

 were impregnated with 9 grains of platinum, by the process just 

 described, the charcoal was found to have undergone no change 

 in its external appearance, though its properties had been very 

 essentially altered. ... I find that 2 per cent, of platinum is 

 sufficient to platinise charcoal for most purposes. Charcoal 

 containing this small amount of platinum causes a mixture of 

 oxygon and hydrogen to combine perfectly in about a quarter of 

 an hour, and this is the strength of platinised charcoal that 

 seems best adapted for charcoal disinfectant respirators. . . . 

 Platinised charcoal seems likely to admit of various useful 

 applications; one of the most obvious of these is its excellent 

 adaptability to air-filters and respirators for disinfectant purposes." 

 So much for the properties of charcoal. My colleague, Professor 

 Corfield, of University College, assures me that " charcoal is now 

 very little used for the purification of foul air. It was formerly 

 employed in sewer ventilation, but it was found that it soon 

 became damp and was then useless." 



I was anxious to test Mr. Toope's application, and to see how 

 far the sulphurous acid of fog might be absorbed as the foggy 

 air passed through the charcoal trays. Mr. Toope therefore, at 

 in) request, furnished me with a sample box, so arranged that I 

 could aspirate air through it. I was frequently in the habit of 

 aspirating fog through 25 c.c. of potassium permanganate of such 



