303 
c. Selenium. As 7; = 973°,1 abs. and 7 — 717°,6 abs. for 
sulphur [444°.55 C. was namely found for 7, by Watpner and 
Buremss (1910), HorBorN and Hennine (1911), Day and Sosman (191 2)], 
the traag dre Teis == 1,36, (it was s=)71, forO,). If in: approxi- 
mation we assume for selenium for 7%: 7’; the same value as for 
sulphur, we find the value 1310° abs. for 7; from 7’,—= 688° C. = 
= 961° abs. [Preuner and Brocxméuumr, Z. f. ph. Ch. 81, p. 146 
(1912). Already in 1902 Berrrnreror gave 690° C.|. From this the 
value 2,375 would follow for 2y, hence y = 1,19. Hence 
Er k hte 
oi 2,19 
For the density of grey Selenium 4,8 or 4,5 was found by. 
SAUNDERS (1900)'). Further SPRING found for the (linear) coefficient 
of expansion between O° and 100° the value 0,00006604. From 
this we calculate for the density at the melting point 220°,2 C.= 
= 493°,3 abs. (Bercer, 1914) D, = 4,61 or 4,32, giving v, = 76,7 
or 81,8.10-°. From this follows therefore with the just found 
value of f, for 4; the value 145 or 155.10-5, while 180. 10-5 is 
expected”) (Ruporr’s value for D, would have given 6;—=163. 10-5). 
If 7, =1810° abs.*), then uw, = 2,655, and hence 
Atl, SBN a. boa. u 02. 
For the attraction of Selenium itself, we find at last with 
bp = 1607. 10- =: 
dr tole x 18010 59328 6 nj == SLE WOE nes 
as 6 —0,9694. As the normal value of Waz, is =7,1. l0-? for Se, 
and therefore a;,=50,4.10~-4, the value 6,18 would follow from 
this for nz, so that at the critical temperature Selenium would on 
an average be — + Se,. But according PREUNER and BrockMOLLER’s 
researches (p. 139 loc. cit.) the dissociation of Se, molecules into 
Se,-molecules would already be complete at 850° C., so that at 
Tj, = about 1040° C. the molecular formula cannot possibly be 
Se,. Even if we take 160 or 170 atm. for the critical pressure, the 
degree of dissociation would be about —1 at this temperature. If 
we assume therefore 7; — 2 (1-2), we find az, =155,9 .10-+(1+ 4), 
or Vax, = 12,49. 10-2 x /(1-+2). 
') In his well-known book on the periodic system (1904) Ruporr gives for the 
density the still lower value 4,26. 
2) From H,Se (see 1) Se = 138.105 is indeed calculated, but this value is 
evidently much too low. 
3) From the vapour-pressure determinations of PREUNER and BrockMörrER (loc. 
cit. p. 146) between 390° and 710° C. we can hardly conclude with any accuracy 
to the values of 7% and px, on account of the great variability of the molecular 
condition between these two temperatures. 
x 0 ad = 2,375 (1— 0,205) = 1,889. 
