METALS IN THE ATMOSPHERE." 



Tly Al.FUEI) DiTTE, 



Mriiihcr of the fiistitiilc of Fidiicc. I'vofcsNitr iif Mlncnil ('Jieiiii.strt/ at the 



SorlKiinic. 



The oarth's atmosphere coiitaiiis an enormous qnantitv of (hist, 

 particles of which float in Ihe air for varyin<>- jxn'iods of time. This 

 (lust is everywhere, in the fichls as well as in town, and Vie only 

 reason wc do not sec it contiiinally is hccansc the j)articles do not 

 ]-('Hcc( cnonu'h liiilit to make an iin|)i-cssion on the retiiia. A I'ay of 

 sunshine in a dai'k room rcNcals the pi'csencc of innnmcrahU^ particles. 



Any jiolished surface e.\|)ose(l to the air will soon be covei'ed with 

 an atnios])heric sediment. All tei-restrial snhstaiices. especially 

 metals, may hy mechanical action he i-educed to a fine powder, lig'ht 

 eiioii«i-h to he cai'ried hy the wind and held suspended in the air. The 

 heatino- of the wa\('s ai^'ainst the shore makes a powder, and the 

 water in e\aporatino- leaves a little saline residue in the air. One 

 can imagine without much difficulty, hut not without a certain (lis<Tiist, 

 the character of the dust ])articles found in city air; they form a 

 means of contact between ])ers()ns widely separated, and to this contact 

 i< due much of the disease common among great aggregations of 

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

 of fermentations, of jnitrefactions, and of various alterations of the 

 blood in epidemic diseases. 



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

 but they may without great difficulty be collected for pur})oses of 

 study. 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. When 

 a sufficient (juantit}^ of air has lieeii run through the air filter the 

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

 it, leaving a residue of dust particles. The insoluble bits of dust are 

 collected by decantation, washed and dried, and then examined under 

 a microscope. 



« Translated fi-oai Revue Scientificine, Paris, .^)tb series. Vol. II, Deeeinber .''>. 

 1904. Opening lecture of course of mineral chemistry, Faculty of Sciences of 

 Paris, November !), 1!)04. 



235 



