DUST. 



By WILLIAM SWAINE. 



In a certain sense we all know what dust is — 

 something very plentiful and often extremely 

 annoying. The housekeeper is plagued very much 

 with it. She sweeps it off the mantelpiece with 

 her cloth, but whither does it go ? In most cases 

 either back again to its old place or on to another 

 piece of furniture which very probably has only 

 just been swept clear of it. Since dust is so plentiful 

 one ought to become extremely familiar with what 

 it is, what it does, what are its advantages and 

 disadvantages, and the reason for its being where 

 it is. But it is very questionable whether we give 

 it very much thought. 



Dust is found over land and sea, but it is obvious 

 that dust must be more plentiful over the land. 

 However, Dr. J. Aitken, of Glasgow, has devoted a 

 large part of his time to the study of its prevalence. 

 In 1891 he devised an instrument, called a " dust 

 counter," by means of which he has detected and 

 counted particles of dust. The following figures 

 are only very approximate : — 



Measurements on Ben Nevis have revealed a 

 diurnal range, maximum in the afternoon (ascending 

 air currents), and minimum in the early morning. 

 Approximately for every three thousand feet 

 ascent the amount becomes four-fifths of the 

 number at the lower level. 



How many dust particles must an inveterate 

 smoker puff out in a lifetime when with one puff 

 he expels 4,000,000,000, and what must be the 

 number from the exhaust of a petrol motor ? 



The number of dust particles has lately increased 

 near country roads owing to the great increase in 

 motor traffic — as we all know to our cost. Tuber- 

 culosis has been noticed to have become more 

 prevalent amongst cattle grazing near a dusty 

 highway, and in fruit-growing districts the dust 

 clogs the pores of the leaves, causing thereby loss 

 to the gardener. 



The causes of excessive dust formation on the 



roads are chemical, physical, and mechanical, and 

 to-day methods of prevention are of two classes — 

 (a) sanitary removal by sprinkling with water or 

 some suitable hygroscopic solid, and (b) tar-spraying 

 the roads. The latter method is now largely adopted. 

 Tar-spraying, however, has its disadvantages. 

 Thus in a recent paper we read of the Carmarthen- 

 shire Main Roads Committee considering a claim 

 for damages from a bee-keeper whose stock, it was 

 maintained, had all died owing to the tar-spraying 

 of the adjacent road. Fish in streams have been 

 poisoned, thus causing an inquiry into the least 

 injurious tar for tar-spraying purposes. Authorities 

 appear to agree in their ideas of a future road. 

 Hubbard suggests " a bituminous concrete surface 

 with a cement concrete base," and this has been 

 tried in the United States with reasonable success. 

 Sir John Macdonald suggests a carpeted road, the 

 carpet to consist of bitumen and laid on a surface 

 of stone held together by some pitchy substance. 



The main causes in the upraising of dust by 

 motors, and so on, are (a) cyclonic air currents 

 produced in the rear, (b) the great tractive force of 

 the hind wheels, together with (c) their uneven 

 turning motion. 



Dusts are either harmless or harmful. The dust 

 which flies about the rooms in bakeries and wood 

 turneries is harmless and, according to some 

 people, fattening. Coal dust and that which 

 hangs about the mills of Lancashire and Yorkshire 

 are more or less harmful. According to certain 

 authorities the coal miner is least troubled with 

 lung diseases. Tin miners, quarrymen, potters, 

 stonemasons, and filemakers are, in decreasing 

 order of magnitude, subject to respiratory diseases. 

 Workers in most chemical works are considerably 

 affected by the corrosive action of the chemical 

 dusts. A visit to a soap works reveals the pre- 

 cautions taken by workers near caustic tanks. 

 Even people outside the works have uncomfortable 

 experiences with floating particles of caustic. 

 Then, again, it is only recently that we have had 

 legislation for the improvement of the conditions 

 for the phosphorus worker. Even now " phossy 

 jaw " is not extinct at these works. 



In 1863 Tyndall wanted to have air freed from 

 dust as far as possible in order to carry on some 

 delicate experiments. This led him to investigate 

 the nature of dust. He found that if the air in a 

 chamber were kept still, the dust settled and could 

 be received as it settled by some suitable liquid, 

 e.g., glycerine. But it was not freed from dust. 

 Hence he adopted the plan of passing air over a red- 

 hot spiral of platinum wire contained in a tube. 

 This was the purest he obtained. Finding in 1878 



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