246 METALS IN THE ATMOSPHERE. 



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

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

 those formed by a supersaturated solution of that salt. It 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 nujst widely varied locations have this 

 same property. Its presence in the air, however, is determined with 

 less certainty than that of the more widely prevalent annnoninm 

 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 tlu^ 

 iiir will do the same, showing that all these bodies contain traces of 

 soda sulphate, somewhat difficult to detect by chemical i)rocesses, but 

 made apparent by using supersaturated solutions of tluit 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 crystallize in a finely 

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

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

 containing sulphate of soda may perhaps account for its presence 

 in the atmosphere. The same is true of any soluble body contained 

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

 and be distributed in small quantities in the surrounding atmosphere. 

 This has been proven in the case of perchloride of iron l)y evaporat- 

 ing a solution thereof above the boiling point of the liquid. 



Still other causes favor the })resence of sulj)hate of soda in the air. 

 Sulphurous gas, suli)hiiretted hydrogen [)rodiiced in the atmosphere, 

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

 contact with salt from the ocean produces a sul})hatc of soda. Again, 

 the carbonate of soda in the presence of calciuju sulphate, and numer- 

 ous other sulphates as well, will give a soda sulphate and some carl)on- 

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

 ways and that in a humid jjorous body it crystallizes so minutely 

 that the least puff' of wind will scatter il cNcrywhei-c. A\'batt'\'cr 

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

 water, it is apparent that sodium in that form is one of the connnonest 

 elements in the atmosphere. 



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

 of meteoric water, is also fouiul in the air. Its presence was deter- 

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

 December, 187-1. But residual dusts from melted i-aiu and snow have 

 no action on the supersaturated solutions of acetate, borate, hyposul- 



