ll 
e. Arsen:cum. The triple point of this substance seems to lie 
at 817° C. according to Govupnau (1914). At least at this tempera- 
ture Arsenicum has been melted under pressure. The boiling point 
(sublimation point at 1 atm.) may be calculated from the series of 
vapour-pressure determinations of Preunur and BROCKMÖLLER (loc.cit.). 
The latter namely found the following sublimation pressures at the 
indicated temperatures, 
t= 400° 45 1° 470° 476° 488° 500° 512° 526° 557° 569° 580° 600° C. 
PaO VO 28:32! 445 °6L" -90: 130-268" 3842-430 1586: pont. 
From this we can calculate pj and 7%, by approximation (see II); 
we then find, also in conneetion with the values of a, and be (see 
further below): 
pr = 95000 mm. = 125 atin. ; 77, = 1320° abs. = 1047° C. 
If with these valnes according to VAN DER Waars’s vapour pressure 
formula we calculate the corresponding values of F, then with 
log*® pe = 4,978 from 
4,978 —log'® p 
EN ee 
where p must be expressed in mm. and 7’ in absolute degrees, we 
find the following values: 
f= 6138 128143 TAS 7161 7737-7835: 199-830 849 °853,-873 
Fi = 4,37 4,48 4,55 4,56 4,54 4,51 4,44 4,39 4,32 4,32 4,28 4,32 
The mean value is /’,,=4,42 (4=10,18); the mean at the four 
highest temperatures is 4,31 (/’-= 9,93). From this latter mean we 
now calculate easily that the value of 7%, that corresponds to 
p == 760 mm., is 7, = 888, ie. ¢; = 615° C. This, therefore, is the 
temperature where the sublimation pressure amounts to 1 atm. (and not 
450° C., as was given by Conecur in 1880. The pressure is then 
only 19 mm. instead of 760 mm. 
From the same formula p„—11720 mm.=15,4 atm. is found for 
the pressure which corresponds to the above given triple point 
817 GC = 1090° abs. 
If the found temperatures are correct, we find 7%: 7, = 1320: 
: 888 = 1,49, a plausible value. [for MN, was found 1,61, for / 
(red) 1,41]. For 7%: 7), we calculate 1320: 1090 = 1,21 (for red 
phosphorus 1,12). 
The high value found for # is not very surprising. For as we 
have found #,=8y in an earlier series of Papers *), and as 
2y = 1 + 0,038 VY T, = 2,38, ie. y—=1,19. is calculated from 
1) These Proc. of March 26, 1914, p. 808; April 23, p. 924; May 29, p. 1047; 
Sept. 26, p. 451. 
1 
