EICHARDS. — A TABLE OF ATOMIC WEIGHTS. 297 



as the minimum.* This method is one in which the tendency of the 

 oxide to retain sulphuric acid is approximately neutralized by the ten- 

 dency of the sulphate to retain water; this fact, which is testified by 

 Baubigny's t good results on zinc, nickel, and aluminium, as well as 

 Marignac's on magnesium.^ The results of Lenssen,§ Partridge, Morse 

 and Jones, II and Bucher, involving the use of cadmic oxalate, all in 

 the neigliborhood of 112, are likely to be too low because of the 

 great difficulty of freeing this substance from water. Morse and Jones 

 have clearly indicated this and other possible causes of error. More- 

 over, I doubt very much if it is possible to prepare the oxalate free 

 from the nitrate by precipitation from solutions containing cadmic nitrate. 

 The method of calculation magnifies either error by introducing it in 

 opposite directions into the numerator and denominator. Bucher's 

 extended work casts grave doubt upon cadmic oxide (used by Morse 

 and Jones, and Lorimer and Smith ^) as a suitable substance to serve 

 for a basis of operations. On the other hand, the work of Huntington ** 

 and Bucher with the bromide (a very satisfactory substance as to its 

 preparation because it may be sublimed, and as to its analysis because of 

 the insolubility of argentic bromide), and that of Bucher with cadmic 

 chloride, point toward 112.3 or 112.4 as the probable figure. The 

 electrolytic work of Hardin f f upon these compounds, performed unfor- 

 tunately with small amounts of material, is nevertheless in favor of the 

 lower value, 112.0 ; so that any value adopted must be uncertain. Clarke 

 computes 111.95 ; for the following table 112.3 has been chosen. 



There is good reason for believing that Clarke's value for calcium 

 (40 07) is probably too high The only determinations worth consider- 

 ing are those of Erdmann and Marchand upon the composition of Ice- 

 land spar, and only one out of their thirteen experiments is corrected 

 for known causes of constant error.|| This experiment, which really 

 constitutes the sum and substance of our pseudo-accurate knowledge 

 of a very important quantity, makes calcium almost exactly 40.0. 



* J. E. Bucher, Johns Hopkins Inaug. Dissertation, Baltimore. (1892.) 

 t Baubigny, Compt. Rend., XCVII. 906, 951, 1369. (1883.) 

 J Marignac, see under magnesium, later in this paper. Compare These Pro- 

 ceedings, XXVI. 260, 273 ; XXXI. 160. 



§ Lenssen, .Journ. prakt. Chem., LXXIX. 281. (1860.) 



II Morse and Jones, Am. Chem. Journ., XIV. 260. 



11 Lorimer and Smith, Zeit. Anorg. Ciiem., I. 364. 



** These Proceedings, (1881,) p. 28. 



tt Hardin, Journ. Am. Chem. Soc, XVIII. 1016. (1096.) 



it Erdmann and Marcliand, Journ. prakt. Chem., L. 237. (1850.) 



