148 Scientific Intelligence. 
SCIENTIFIC INTELLIGENCE, 
-J. CHEMISTRY AND PHysics. 
1. On Isopyenic curves.—VON WROBLEWSKY proposes to rep- 
resent graphically the relations between the liquid and the gaseous 
states of matter by a system of equal density curves, which he 
calls isopyenic lines. Hitherto these relations have been graphi- 
cally represented by curves of uniform temperature (isothermals) 
in which the pressure and the volume are the variables. In the 
new method the temperatures are laid down as abscissas and the 
pressures as ordinates. In the memoir the application of the 
method is shown for carbon dioxide, one of the substances for 
which the observed data are the most complete. An inspection 
of the curve shows distinctly that our knowledge of changes of 
state such as these is, especially in the vicinity of the liquefying 
point, very incomplete and in part incorrect. Moreover the 
author concludes that, even above the so-called critical tempera- - 
ture, there is a distinct difference between the liquid and the 
gaseous states, although this difference is very small.— Wien. 
Monatsb. f. Chem., vii, 383; Ber. Berl. Chem. Ges. xix, 728, 
(Ref) Nov. 1886. G. F. B. 
2. The Vapor-pressure of Hydrated Salts—Mtiier Erzpacu 
has continued his researches upon the constitution of hydrated 
salts as determined from the pressure exerted by the vapor of the 
water they contain, measured at ordinary temperatures. This he 
experimentally determines from the loss of weight which two 
identical tubes, one of which contains the hydrated salt in ques- 
tion, the other water, simultaneously suffer, when placed in an 
atmosphere dried by means of sulphuric acid. The ratio of this 
loss of weight in the two cases the author regards as rigorously 
equal to the ratio of the elastic forces of the water vapor in the 
two tubes. Measured in this way, he finds that the evaporation 
from hydrated salts in completely dry air gives constant dissocia- 
tion-pressures. ‘The present paper gives the results obtained with 
nitrates and hydrates. Calcium nitrate for example, CaN,O,. 
(H,O), loses its water under a dissociation-pressure of 0-06 to 
0°07. A white crystalline mass, left after evaporating an aqueous 
solution of the nitrate over sulphuric acid in rarefied air, con- 
tained only three molecules of water, of which one was given up 
at a pressure of 0°10 to 0-11, while the two others were evolved 
at the lower pressure of 0°04.. Hence the author represents the 
Ca N,O,+(H,9), 
H,O : 
cule of water be added, about one-half of this water is evolved 
under the pretty constant pressure of 0°27 to 0°36; the pressure 
then falls to 0°08 to 0°07, and before this water is entirely given 
up, the pressure reaches 0°04, as above. Strontium nitrate, 
constitution of this salt as If a fourth mole- 
