Chemistry and Physios. 439 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Atomic Weights of Silver, Nitrogen and Sulphur. — The 

 masterly researches conducted by Prof. Theodore W. Richards 

 are being continued with apparently still more wonderful preci- 

 sion than heretofore. Richards and Forbes have studied the 

 quantitative synthesis of silver nitrate. For this purpose they 

 employed a bulb of fused quartz for evaporating and drying the 

 silver nitrate produced by dissolving pure silver in pure nitric 

 acid. They found that 100,000 parts of pure silver produce 

 151-4:19 parts of silver nitrate. If silver is assumed to be 107*93, 

 nitrogen must be 1 4*037, while if silver is taken as 107*880, nitro- 

 gen must be 14-008. The question of the exact atomic weight 

 of silver must be determined by further work, particularly 

 upon the composition of the chlorates and the ammonium salts. 



Richards and Jones have investigated the comparative 

 weights of silver sulphate and silver chloride, carrying out the 

 conversion in a tube of fused quartz. They found that 100*000 

 parts of silver sulphate gave 91*933 parts of silver chloride, and 

 calculated, if silver is taken as 107*93, sulphur is 31*113, while if 

 silver is 107*88, sulphur is 32*069. The final decision in regard 

 to the atomic weight of sulphur must await further work upon 

 that of silver. — Carnegie Inst. Pub. 69 (1907). h. l. w. 



2. The Atomic Weight of Radium. — Mdme. Curie made 

 determinations of this atomic weight in 1902, using nine centi- 

 grams of radium chloride. With this small quantity the value 

 225 was obtained. Having now at her disposal a few decigrams 

 of the salt, she has carefully purified it, and has obtained four 

 decigrams of very pure radium chloride, upon which she has car- 

 ried out three determinations under much more favorable condi- 

 tions than before. The determinations were made by comparing 

 the weights of anhydrous radium chloride with the weights of 

 silver chloride produced from them. The results led to the con- 

 clusion that the atomic weight of radium is 226*2, where Ag is 

 107*8 and CI is 35*4, with a probable error of less than half a 

 unit. If the international atomic weights for silver and chlorine 

 are used as a basis, the value is Ra=226*45. The radium salt 

 was not absolutely free from barium, as shown by the spectro- 

 scopic test, but it is the author's opinion that the trace of impur- 

 ity present had an inappreciable effect upon the results, and it is 

 her opinion that the difference between the results of 1902 and 

 1907 should be attributed to the inferior accuracy of the experi- 

 ments performed with only nine centigrams of radium salt, and 

 with less pure reagents. — Cotnptes Pendus, cxiv, 422. 



H. L. AV. 



