( 560 ) 
for which 7; is a minimum. But it may be advisable to wait with 
the discussion of this and similar cases till an experimental inves- 
tigation has brought them to light. 
If by increase of temperature the surface of coexistence has so 
far contracted that it no longer covers the whole triangle oy, a 
tangent cylindre may be drawn normal to the zy-surface. All the 
points, in which the tangent cylindre and the surface of coexistence 
touch, represent mixtures which are in critical tangent-point cir- 
eumstance. A plaitpoint can never lie on this apparent circumference 
of the surface of coexistence, except in some special cases. For as 
the generatrices of this tangent cylindre are parallel to the volume- 
axis and p must have the same value for the pair of phases coin- 
ciding in a plaitpoint, we have 
dp 
dv? 
7 05 d°5 
for such a special case. In order not to have a8 OT aa negative, 
ca he Yi 
ow Oak A 
and — — must be equal to 0. Such a mixture behaves asa 
da dv dy dv 
simple substance even under critical circumstances. See for a similar 
circumstance with a binary system Cont. II page 116. So the 
plaitpoints lie either on the liquid sheet, or on the vapour sheet of 
the surface of coexistence. In the first case all mixtures, indicated 
by points of the «y-surface, lying between the section of the tangent 
cylindre and the projection of the curve on which the plaitpoints 
are situated, have retograde condensation of the first kind. If the 
plaitpoints lie on the vapour sheet, then such mixtures have r. c. II. 
(To be continued). 
Physics. — “On the asymmetry of the electro-capillary-curve.” By 
Dr. J. J. van LAAR (communicated by Prof. van DER WAALS). 
I. We may suppose, that it is well known, that the new theory 
of the so called Capillary-Electrometer of LippMANN may be described 
as follows. 
Two mercury surfaces, one large (A), the other small (B) — this latter 
in the so called capillary — are separated by a conductive liquid 
C, diluted Hs SO, a solution of KCl, or any other solution, In all 
