METALS IX THE ATMOSPHERE." 



T'.y Ar.KREi) Drni:, 



Mriiihcr iif llic hislHiitc of I'm-iicc. I'rofcssnr of Mineral Chriuislrii at the 



Horlioinir. 



The onrlh's atniosi^hore contains an enormous qnantitv of dust, 

 particles of which float in (he air for varying periods of time. This 

 dust is everywhere, in the fields as well as in town, and -^le only 

 reason we do not see it continually is because the particles do not 

 i-eflect enouiih light to make an imi)ression on the retina. A ray of 

 sunshine in a dark room reveals the [)resence of innumerable particles. 



Any jiolished surface exposed to the air wall soon be covered with 

 an atmospheric sediment. All terrestrial substances, especially 

 metals, may by mechanical action be reduced to a fine powder, light 

 enough to l)e carried by the wind and held suspended in the air. The 

 beating of the waves against the shore makes a powder, and the 

 water in evai)orating leaves a little saline residue in the air. One 

 can inuigine without nmch difficulty, but not without a certain disgust, 

 ihe character of the dust particles foimd in city air; they form a 

 means of contact between persons widely separated, and to this contact 

 i< due nmch of the disease connnon among gi-eat aggregati(ms of 

 people. Some of these innumerable corpuscles are bound to be germs 

 of fermentations, of i)utrefacti()ns. and of various alterations of the 

 blood in epideuiic diseases. 



Not only are all these solid substances visible with sufficient light, 

 but they may without great difficulty be collected for purposes of 

 >tudy. Pasteur was the first to devise a method of so doing by draw- 

 ing the air through a tube containing a wad of nitrated cotton. AMwn 

 a sufficient <|uantity of air has been run through the air filter the 

 cotton, with its deposit of dust, is treated with ether, which dissolves 

 it. leaving a residue of dust particles. The insoluble bits of dust ai'e 

 collected by decantation. washed and di'ied. and theu examiueil under 

 a microscoi)e. 



"Translated from Revue Seientifique, Paris, .5th series, Vol. II, December .^, 

 l!tu4. Oiteulii.s,' lecture of course of mineral chemistry. Faculty of Sciences of 

 Paris. Xovember J), 1904. 



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