li 
( 105 ) 
was exhausted from the whole apparatus, and by passing an electric 
current through the wires 7 U7", the tube was heated till it burst. 
While the bulb P was constantly kept at 0°, the refractivity of 
the gas could be determined, by changing the pressure of the 
gas in the other side of the apparatus, till the interference phenome- 
non reached again the normal position and by reading this pres- 
sure and that of the gas. On account of the great refractivity of 
the gases, air could not be used as the gas, serving for comparing 
them; I have therefore used carbonic acid. 
The investigation was made with ethylether and acetone; both 
from MERCK in Darmstadt. 
These substances were chosen because at 0° they have a vapour 
tension of less than one atm., and yet it is large enough to be 
measured pretty accurately; moreover the refractivity of the gases 
had to differ as much as possible. 
‘The compositions of the liquids was obtained by weighing, while 
the weights of the quantities of each of the two substances in the 
vapour were afterwards subtracted from the original quantities. 
The results are given in Table II (see also fig. 3) ether being 
considered as the solved substance. 
TAB LE IL 
Refractivity. To td p in mm. 
3.7788 0. 0. 69.6 
4.4956 0.156 | 0.446 110.5 
4.7709 0.364 | 0.617 142.4 
4.8552 0.510 | 0.670 159. 
4.9497 0.617 | 0.728 166.8 
5.1636 0.835 | 0.861 181.2 
5.3869 1s i: 185.6 
They give rise to the following observations. There is no maxi- 
mum or minimum pressure; so the mixture belongs to what Harr- 
MAN calls the first type. There is greater difference in the composition 
of the liquid and the gas when a little ether is mixed with acetone, 
than when a little acetone is mixed with ether. 
The curve representing the pressure as function of the composition 
of the vapour (p» =/ (ra) in fig. 3), shows a point of inflection 
8* 
