238 METALS IN THE ATMOSPHERE. 



on June 1, 10, and 11, 1876, amounted to from 23 to 75 mg. per liter; 

 at Paris it has run from '28 to 172, the maximum being 421 mg. This 

 residue is bhickish gmy^ except that collected in the fields, which is 

 entirely'' white, and it invarial)ly contains the same relative propor- 

 tions of mineral substances and organic matter. 



The size of snoAvflakes and the leisurely manner in which these 

 little spongy masses fall through the air makes them even better 

 litted than rain drops to seize in their passage all the dust particles 

 and solid bodies floating in the atmosphere. Moreover, solids are col- 

 lected in the waters fused into the flake. Consequently, when Mon- 

 sieur Tissandier collected with all proper precaution the first snows 

 that fell on the towers of Notre Dame in the winter of 1875, he found 

 in each liter of the snow water a body of corpuscles varying in weight 

 from 56 to 118 mg. A liter of melted snoAV collected under the same 

 conditions in the country contains from 48 to 104 mg. Further- 

 more, as one might suppose, the corpuscles are less numerous after a 

 prolonged snoAvstorm, so much so that in Paris, after a heavy fall, 

 only 16 to 24 mg Avere found. The residue obtained by the evapora- 

 tion of melted suoaa- is ordinarily an impalpable grayish poAvcler, con- 

 taining, at Paris, al)out 57 per cent of cinders, and in the country 

 about 61 per cent. 



Hail, because of its small size and its great density, does not collect 

 the dust particles so easil3^ Nev^ertheless, it has been collected and 

 examined in the same way. 



Iro7i. — The examination of the cinders m the dust collected in these 

 various ways enables us to recognize in our atmosphere the jjresence 

 of a number of metals, the most important of Avhich is iron. 



When a strong magnet was held near some of the atmospheric sedi- 

 ment thus obtained, a portion of the corpuscles adhered to it ;in(l were 

 brushed off for microscopic or chemical examinations. It was then 

 discovered that these bits are made up essentially of iron. The same 

 results Avere obtained with sediments collected in seA'^eral very ditfer- 

 ent localities. The examinations even AAent so far as to estimate ap- 

 l)roximately the quantity of iron contained in this magnetic residue 

 by the intensity of the coloration of sulphocyanicle of jjotassium in the 

 dissolution of a knoAA'n quantity of dust. These ferruginous i)articles 

 were found to be either pure iron or tliat metal associated in cei'tain 

 l)roportions Avith other elements, such as uick(>l and i)h()sphorus. M. 

 Nordenskicild, at Stockholm in 1871, examining the surface of the 

 greatest fall of snoAV Avithin the memory of man, found small quanti- 

 ties of metallic ii-ou. P)ut fearing this might haA^^e come from neigh- 

 boring roofs, he had his brother examine the snoAV in a desolate plain 

 surrounded by the forests of Finland. The black poAA'der secured 

 there was of the same character as that of Stockholm. The particles 

 of iron draAvn out bv a magnet, Avhen triturated in an airs^te mortar. 



