APPENDIX II. 485 



Hum chloridey/BeClj, obliges us to regard beryllium as bivalent in 

 conformity witji the periodic law. 7 I consider the confirmation of Avde*efFs 

 and Braunery view as important in the history of the periodic law as the 

 discovery of scandium, which, in Nilson's hands, confirmed the existence of 

 ekaboron. 



The circumstance that thorium proved to be quadrivalent, and Th = 232, 

 in accordance with the views of Chydenius and the requirements of thl 

 periodic law", passed almost unnoticed, and was accepted without opposition, 

 and yet both thorium and uranium are of great importance in the periodic 

 system, as they are its last members,. and have the highest atomic weights of 

 all the elements. 



The alteration of the atomic weight of uranium from U = 120 into U = 240 

 attracted more attention, the change having been made on account of the 

 periodic law, and for no other reason. Now that Roscoe, Rammelsberg, 

 Zimmerman^) and several others have admitted the various claims of the 

 periodic law in the case of uranium, its high atomic weight is received .with- 

 out objection, and it endows that element with a special interest. 



While thus demonstrating the necessity for modifying the atomic weights 

 of several insufficiently known elements, the periodic law enabled us also to 

 detect errors in the determination of the atomic weights of several elements 

 whose valencies and true position among other elements were already well 

 known. Three such cases are especially noteworthy: those of tellurium, 

 titanium and platinum. Berzelius had determined the atomic weight of 

 tellurium to be 128, while the periodic law claimed for it an atomic weight 

 below that of iodine, which had been fixed by Stas at 126*5, and which was 

 certainly not higher 'than 127. Brauner then undertook the investigation, 

 and he has shown that the true atomic weight of tellurium is lower than that 

 of iodine, being near to 125. For titanium the extensive researches of 

 Thorpe have confirmed the atomic weight of Ti - 48, indicated by the law, 

 and already foreseen by Rose, but contradicted by the analyses of Pierre and 

 several other chemists. An equally brilliant confirmation of the expectations 

 based on the periodic law has been given in the case of the series osmium, 

 iridium, platinum, and gold. At the time of the promulgation of the periodic 

 law, the determinations of Berzelius, Rose, and many others gave the follow- 

 ing figures : 



Os = 200; Ir = 197; Pt = 198; Au = 196. 



7 Let me mention another proof of the bivalency of beryllium which may have passed 

 unnoticed, as it was only published in the Russian chemical literature. Having remarked" 

 (in 1884) that the density of such solutions of chlorides of metals, MCl n , as contain 200 

 mols. of water (or a large and constant amount of water) regularly increases as the mole- 

 cular weight of the dissolved salt increases, I proposed to one of our young chemists, 

 M. Burdakoff, that he should investigate beryllium chloride. If its molecule be BeGlj 

 its weight must be =80; and in such a case it must be heavier than the molecule of 

 KC1 = 74-5, and lighter than that of MgCl 2 = 93. On the contrary, if beryllium chloride is 

 a trichloride, BeCl 3 = 120, its molecule must be heavier than that of CaCl 2 = lll, ind 

 lighter than that of MnCl 2 = 126. Experiment has shown the correctness of the fonrier 

 formula, the solution BeCl 2 + 200H 2 O having (at 15/4) a density of T0138, this being a 

 lugher density than that of the solution KC14-200H 2 O ( = 1'0121), and lower than that of 

 MgCl 2 +200H 2 O ( = 1-0203). The bivalency of beryllium was thus confirmed in the case 

 both of the dissolved and the vaporised chloride. 



