138 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Dumas 8 titrated the trichloride of phosphorus against silver after 

 decomposing the trichloride with water. Since the sample used did 

 not boil at constant temperature, but distilled between 76° and 78°, it 

 must have been impure. If it contained oxychloride, as Clarke has 

 suggested, the atomic weight of phosphorus would be found too high. 

 Dumas overlooked the solubility of silver chloride and therefore used 

 the wrong end-point in these titrations. Furthermore no precautions 

 are mentioned either for preventing access of water to the material 

 before weighing or for preventing the reduction of the silver salt by 

 the phosphorous acid formed in the decomposition of the trichloride 

 with water. Recalculated on the basis of the atomic weight of silver 

 as 107.88, his five analyses give results which vary between 30.99 and 

 31.08. The average is 31.03. 



Van der Platts 9 made two determinations by each of three different 

 methods. He obtained the values 30.90 and 30.97 by the precipitation 

 of silver from silver sulphate solution with phosphorus. His results 

 from the analysis of silver phosphate were 31.08 and 30.95. He gives 

 no details of the method of preparing and analyzing this substance, 

 merely making the statement, " It is difficult to be sure of the purity 

 of this salt." Finally, by the combustion of yellow phosphorus in 

 oxygen he obtained the results 30.99 and 30.96. The very meagre 

 descriptions of these experiments preclude criticism. 



Using Leduc's data for the densities and compressibilities of phos- 

 phine and oxygen, Daniel Berthelot 10 has calculated, by the method of 

 limiting densities, the molecular weight of phosphine to be 34.00 and 

 the atomic weight of phosphorus to be 30.98. 



Very recently Gazarian 1X has obtained a considerably lower value for 

 the molecular weight of phosphine, 33.93. This value was calculated 

 from the experimentally determined weight of the standard liter by the 

 four methods of molecular volumes (Leduc), limiting densities (Berthe- 

 lot), critical constants (Guye), and " indirect " limiting densities 

 (Berthelot). The different methods give essentially identical results, 

 except in the case of the direct method of limiting densities. By the 

 latter method a value six-hundredths of a unit higher is obtained, but 

 Gazarian rejects the result on the basis of inaccurate knowledge of the 

 compressibility of phosphine. It is highly desirable to obtain more 

 certain knowledge of the compressibility of phosphine, since the 



8 Ann. Chem. Pharm., I860, 113, 28. 



9 C. R., 1885, 100, 52. 



10 C. R., 1898, 126, 1415. 



11 Jour, de Chim. Phys., 1909, 7, 337. 



