[ 280 ] 
XXIV. On the Atomic Weight of Radium. 
By Henry Wilde, JD.Sc, D.C.L., F.R.S.* 
IN my paper read before the Society last year f, it was 
shown from the relations o£ the specific gravities of the 
alkaline-earth metals to their atomic weights, and also from 
the similar relations of the series of alkaline metals, that 
radium would have a proximate specific gravity of 5, and an 
atomic weight of 184, notwithstanding the assertions that 
have been made that the new element would be a heavy 
metal comparable with thorium (sp. gr. 11) and uranium 
(sp. gr. 18), and that its atomic weight ranged between 225 
and 258. It was also shown that the atomic weights of the 
two series Hn and H2n of my tables, are definite multiple 
differences and not intermediate numbers. 
In the several accounts which have been given of the 
atomic weight of radium, it is stated that the experimental 
determinations were made with radium chloride. Now it is 
well known to chemists that the series of alkaline metals and 
alkaline-earth metals, magnesium, calcium, strontium, and 
barium, unite with chlorine in one proportion only. 
An important gain to chemical science which the multiple 
differences of the atomic weights have led up to, is the 
quantitative determination of the combining proportions of 
new elements in anticipation of the experimental results. 
Taking the instance of radium chloride, I have estimated 
its combining weight after the classical method of Marignact 
and Dumas § in their experimental determination of the 
atomic weight of barium as follows : — 
1. One part of silver corresponds to 1*176 parts of 
radium chloride, or . 
2. The atomic weight of silver being 108, we have radium 
chloride = 1-176 x 108 = 127 minus 01 (35) =92 the 
combining weight of radium with chlorine. 
3. Now 2x92 = 184 is the bivalent atomic weight of 
radium with bivalent oxygen in the positive and 
negative series H2n, as showm in my general Table, 
with a possible increase of one unit in the experi- 
mental determination, as in the instance of barium 
(136-137). 
* Reprinted from the Memoirs and Proceedings of the Manchester 
Literary and Philosophical Society, vol. lii. pt. 1 (1907). From a 
separate copy communicated by the Author. 
t Manchester Memoirs, vol. li. ]S T o. 2 (1906). 
X Bibl. Univ. Archives, 1858, p. 81. 
§ Ann. Chim. Phys. vol. lv. p. 139 (1859). 
