( 320 ) 
By the three figures 16, 18 and 19, the fact is made intelligible, that 
sensation is lost towards the mid-ventral, not towards the mid-dorsal 
line. For this fact again the contrast between central and marginal 
areas of the dermatoma is necessary. Only by a quite separate series 
of experiments however, concerning sensibility in the middle of the 
dermatomata, (on the spot where the central area possesses a minimum 
of innervation) can it be made clear where the top of the insensible 
area must be situated, and in what manner is caused the interruption 
in the analgetic zone when two roots are sectioned. 
Physics. — Dr. Pu. A. Konystamm on: ‘The shape of an empiric 
isothermal of a binary mixture.’ (Communicated by Prof. 
J. D. VAN DER WAALS). 
In § 8—§ 10 of my thesis for the doctorate I have discussed the 
shape of the empiric!) isothermal of a binary mixture. Without 
writing it down, I start there ®) from the equation: 
v = Vol + Vd 
where vj and vg represent the actually measured volumes of liquid 
and vapour, and v the total volume. If we assume that we have 
to deal with a molecular quantity, v is at the same time the molecular 
volume of the mixture; v‚7 and vg, however, are no molecular volumes. 
Now I have shown, that the shape of the course of v as function 
of p, so also the shape of the empiric isothermal cannot differ sensibly 
A from the shape of the course of vg and after 
having drawn up a formula for vg, I derive 
by differentiating this formula the shape of 
the empirie isothermal. 
Perhaps we can arrive at this fundamental 
formula in a simpler way by not starting 
from the really measured vapour- and liquid 
volumes, but from the molecular volumes. 
x We have then (see fig. 1): 
Fig 1. 
' ' . 
Tg — x TL — A 
= Vy + vd 
Peg tee a ED rd 
*) I speak there of derived” isothermal. The name chosen here is perhaps clearer. 
*) p. 141. 
