298 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Obviously but little confidence may be placed in such meagre material ; 

 it is surprising enough that so common an element has remained forty 

 years untouched on so unsatisfactory a basis. An extended investiga- 

 tion, now well advanced in this Laboratory, has as its object the securing 

 of less impeachable data upon the atomic weight of this frequently 

 appearing constituent of the universe. 



Marignac's* results from the quantitative ignition and synthesis of 

 magnesic sulphate, processes in which the constant errors are likely to 

 eliminate one another, have been so completely confirmed by the recent 

 work of Richards and Parker,t that magnesium is represented by the 

 fio-ure 24. 3G in the table. The results of the syntheses of magnesic 

 oxide by Burton and Vcrce t have been shown by Richards and 

 Rogers § to be under the cloud of a serious possible constant error, 

 and no other results offer weighty evidence against the value just 

 named. 



An important deviation from the usually accepted figures is to be seen 

 in the value assigned to platinum below. Our knowledge of the atomic 

 weight of this element depends chiefly upon the elaborate and carefully 

 executed work of Seubert || and Halberstadt,^ and the only question 

 is how this is to be interpreted. These chemists studied the platin- 

 chlorides and platinbromides of potassium and the platinchloride of 

 ammonium, weighing these compounds and some of the products of 

 their decomposition. The careful study of the results shows at once 

 that some source of error lies hidden in all the data, for the various ratios 

 are not wholly consistent, even in any one series. Any value from 

 194.7 to 196. maybe obtained from the figures,** the results of Seubert's 

 work being the least discordant among themselves. Dittmar and 

 M' Arthur ft explain the discrepancies in the case of potassic platin- 

 chloride by assuming that the complex salt contains traces of hydioxyl 

 replacing the halogen and traces of hydrogen replacing the potassium, 

 as well as a small amount of extra occluded potassic chloride. They 



* Marigiiac, Arch. Sci. Phys. et Nat., (3), X. 206. 



t Kichards and Parker, These Proceedings, XXXII. 53 ; Zeit. Anorg. Chem. 

 XIII. 81. (1806.) 



t Burton and Vorce, Am. Ch. Journ., XII. 219. (1890.) 



§ Richards and Rogers, These Proceedings, XXVIII. 200. 



II Seuhert, Ber. d. d. chem. Geseli., XIV. 865. (1881.) 



1 Ilalberstadt, Ibid., XVII. 2962. (1884.) 



** Clarke, Recalculation, (1897,) p. 334. 



ft Trans. Roy. Soc. Edinburgh, XXXIII. Part II. 561. (1887.) 



