RICHARDS AND ARCHIBALD. — ATOMIC WEIGHT OF CAESIUM. 463 



The average of these results (39.141) agrees well with that obtained 

 from the chloride (39.139), and the constancy of the results indicates 

 that the method is adequate for its purpose. 



VII. The Analysis of Caesic Nitrate. 



The decomposition of caesic nitrate may be effected in precisely the 

 same fashion as that of potassic nitrate. The only points to be considered 

 especially are the preparation of the pure salt and the data necessary for 

 reduction to the vacuum standard. 



Very pure caesic nitrate prepared from the four times recrystallized 

 dichloriodide, and subsequently twice recrystallized, had already been 

 prepared for us by Professor Wells. Like potassic nitrate, it is very 

 easy to recrystallize.* 



After gentle fusion this preparation was finely powdered, and served 

 for the first two analyses. In order to test its purity, a portiou was 

 twice recrystallized in platinum vessels, very carefully fused in platinum, 

 powdered as before, and subjected to analysis. Because the results were 

 identical with those obtained from the first sample, further purification 

 seemed unnecessary. 



No measurements of the specific gravity of caesic nitrate could be 

 found, therefore this constant was determined, since its value is needed 

 in order to find the weight of air displaced. 1.7638 grams of fused 

 caesic nitrate displaced upon one occasion 0.4210 gram and at another 

 time 0.4208 gram of rectified benzol at 28° C. The specific gravity of 

 the benzol was 0.880, 20° /4° ; therefore the specific gravity of the 

 caesic nitrate must be 3.687. 



In determining the air displaced by caesic oxide when combined with 

 silica, the only fact available is the density of the hydrate. If we assume 

 that the same contraction takes place when caesic oxide combines with 

 water as when it combines with silica, the specific gravity of caesic oxide 

 under these conditions is easily computed to be 4.9 if caesic hydroxide 

 has a specific gravity 4.0, t as follows. Twice the molar volume of 

 caesic hydroxide is 57 c.c. greater than that of water, and if the molar 

 weight of caesic oxide is divided by this difference, the result given above 

 is obtained. This assumption would have given in the case of potassium 

 about the same result as that used under that head ; and while it is of 

 course inexact, it will answer sufficiently well the present purpose. In 



* Wells, Am. J. Sci., 3, 46, 186. 



t Bckctoff, Bull. Acad. St. Petersb., 2, 171 (1890) ; Ch. Centralbl., 2, 451 (1891). 



