ON THE EFFECTS OF URBAN FOG UPON CULTIVATED PLANTS. 145 



The Meteorological Council very readily put at our disposal 

 the pump and apparatus originally constructed for Dr. W. J. 

 Russell's investigation. The whole apparatus was thoroughly 

 revised and set up under the direction of Dr. Russell. Since 

 the middle of December frequent washings of fog have been 

 obtained with it. Those are now undergoing analysis. In 

 addition, samples of many fogs have been aspirated through a 

 solution of permanganate of potash — the volume of fog necessary 

 to decolourise the pink solution being registered by a meter 

 constructed on the wet system. 



The permanganate is extremely susceptible to sulphurous 

 acid, probably the chief agent of damage present in the London 

 atmosphere. A comparison of the volumes of air necessary to 

 completely bleach a known amount of permanganate in foggy 

 and in fine weather is striking. Whilst during a severe fog 

 as little as 1 or 2 cubic feet is sufficient, in fine clear weather 30 or 

 40 cubic feet may be aspirated without causing an appreciable 

 decolouration. Even a rough method such as this would 

 become an instrument of some precision in the hands of a 

 chemist, and would furnish results of the greatest value 

 in comparing the damage to vegetation inflicted by separate 

 fogs. 



During the winter, collections of snow from equal areas were 

 made at frequent intervals, and the amount of matter precipi- 

 tated upon it from day to day estimated. 



At the close of the February fogs the opportunity was taken 

 to make scrapings from 20 square yards of the glass roofs of 

 plant houses at Kew and at Chelsea. The glass at both 

 localities had been washed just before the commencement of 

 the spell of fog. Each yielded an almost identical amount 

 of deposit — i.e., 31 grains per square yard or 6 tons per square 

 mile. 



Dr. G. H. Bailey, of the Owens College, Manchester, was 

 good enough to analyse the samples and furnishes the following 

 as the result of a preliminary examination of that from Chelsea : 

 " It consisted of about 40 per cent, of mineral matter, 36 per 

 cent, of carbon, and 15 per cent, of hydro- carbons. It was 

 interesting to note that there was present also 2 to 3 per cent, 

 of metallic iron in minute particles. The sulphuric acid present 

 amounted to nearly 5 per cent., and the hydrochloric acid to 



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