246 METALS IN THE ATMOSPHERE. 



Sulpliate of soda. — Sulphate of soda is frequently found in the 

 matter soluble in Avater, and it crystallizes in four-sided prisms, like 

 those formed by a supersaturated solution of that salt. Tt is only 

 necessary to introduce into one of these solutions a few flakes of snow 

 to determine immediately its crystallization. Monsieur Goernez has 

 shown that deposits from the most widely varied locations have this 

 same property. Its presence in tlie air, hoAvever, is determiiuMl with 

 less certaint)^ than that of tlic more widely prevalent anmioniiim 

 nitrate, and the atmospheric deposits show in every case the crystalli- 

 zation of a supersaturated solution of that nitrate. Not only has 

 Monsieur Goernez demonstrated that flakes of snow or solid atmos- 

 pheric sediments will determine the crystallization of supersaturated 

 solutions of soda sulphate, but that almost all bodies exposed to the 

 air will do the same, showing that all these bodies contain truces of 

 soda sulphate, somewhat difficult to detect by chemical processes, but 

 made apparent by using supersaturated solutions of that salt as 

 reagents. 



The prevalence of soda sulphate is everywhere demonstrated, and 

 since that salt exists in water, mineral, river, or sea, it is naturally 

 found in the soil. Having a tendency to ciTstallize in a lincly 

 divided state on the surface of a porous body, the least wind will 

 carry it off' and deposit it elsewhere. Simple evaporation of waters 

 containing sulphate of soda may perhaps account for its presence 

 in the atmos})here. The same is true of an}^ soluble body contained 

 in water; the salt thus dissolved maj' be carried off' by evaporation 

 and be distributed in small quantities in the sun-ounding"atmospliei-('. 

 This has been proven in the case of perchloride of iron by evaporat- 

 ing a solution thereof above the boiling point of the li({uid. 



Still other causes favor the presence of sulphate of soda in the air. 

 Sulphurous gas, sulphuretted hydrogen i)roduced in the atmosphere, 

 is there easily transformed into sul})huric acid auvl on coming into 

 contact with salt from the ocean produces a sidphate of soda. Again, 

 the carbonate of soda in the presence of calcium sul])hate, and numer- 

 ous other sulphates as well, will give a soda sul])hat(' and some carbcm- 

 ates. So it is established that sulphate of soda is formed in various 

 ways and that in a humid j)or()us body it crystallizes so minutely 

 that the least puff' of wind will scatter it cxcrywhere. Whatever 

 may be the origin of sulphate of soda, which is in the eartli and 

 water, it is a[)parent tlnit sodium in that foi'm is one of the conuuonest 

 elements in the atmosphere. 



Seasalt. — Sea salt, which will crystallize in cubes on the evaporation 

 of meteoric water, is also found in the air. Its ])resence was deter- 

 mined in melted snow collected on the lofty tower of Xotre Dame in 

 December, 1874. But residual dusts fi-om melted rain and snow have 

 no action on the supersaturated solutions of acetate, borate. hy])osu]- 



