’ FUNDAMENTAL PROPERTIES OF THE ELEMENTS—RICHARDS. 207 
greater than the contraction which takes place on forming several 
other oxides, and he ascribed this effect to the well-known differences 
of affinity in these cases; but he did. not carry the idea further. 
Long afterwards, Braun, Mueller-Erzbach,? Hagemann,’ and Traube,‘ 
independently and apparently without knowledge of each other’s 
work, called attention to other cases of similar relationships. 
All of these researches have produced so little effect on the litera- 
ture of the subject® that they were entirely overlooked during the 
COMPARISON of HEATS OF FORMATION of CHLORIDES 
and CONTRACTION ON COMBINATION 
200 HEAT OF FORMATION 
CAL 
“CONTRACTION \ 
ON COMBINATION 
10 
0 
Fia. 2. 
earlier part of the present investigation. The oversight mattered 
little, however, because the whole subject needed a fresh attack. 
Essential factors in the situation had not been noticed by any of 
these earlier investigators. Affinities, indeed, had been considered, 
but the nature of the substances on which the affinities act had been 
overlooked. Evidently the change of volume in any case must de- 
pend not only on the intensity of the pressure exerted by the affinity, 
but also, among other things, on* the compressibility of the sub- 
1 V. Braun, see Johnson, Journal Chemical Society Transactions, 1877, vol. 31, p. 252. 
2 Mueller-Erzbach, Ber., d. deutsch. Ch. Ges., 1881, vol. 14, pp. 217, 2043. 
3 Hagemann (private publication, Friedlander, Berlin, 1900). 
4 Traube, Ueber den Raum der Atome, Ahrens’s Sammlung der chem. und chem.-techn. Vortrige, vol, 
4, p. 256. 
5 See, for example, Ostwald’s Gundriss der allgemeinen Chemie, 1899, p. 185, 
