121 
by means of a siphon-shaped tube. The filling of the pipettes J with 
the solution from B took also place by pressing in of dry air 
through tube H, after the capillary of the pipette had been immersed 
through G in the solution; a rubber ring, put round the capillary, 
ensured air-tight closure. 
When the pipette is closed in the way as is seen in the figure, 
it is possible to preserve the liquid quite unchanged for 12 hours. 
The vessels were always cleaned with benzene instead of alcohol 
and ether, because the latter causes water-vapour to condense on 
the glass in case of quick evaporation. Before the filling with liquid 
the vessels were filled with dry air. 
The brass closing blocks also protect the liquid sufficiently against 
absorption of water-vapour from the atmosphere, so that the inter- 
ferometer position does not appreciably change during the~time 
taken up by a determination. It is true that in the course of some 
hours the zero position is slightly displaced in consequence of ab- 
sorption of water by the pure solvent in vessel-C,; this displacement 
can, however, easily be determined and taken into account. 
12. Only when the precautions described here are observed, is 
it possible to obtain an accuracy and reproducibility, almost equal 
to that which is reached for aqueous solutions. 
In conclusion we may give a series of measurements referring to 
solutions of C,H,Br, and C,H,Cl, of different concentrations. With 
every solution two independent measurements were made (also the 
zero-position was determined every time anew). The measurements 
are reduced to vacuum. Just as before a vessel of 2 cm. was used. 
EE observed number of | f | | concen- 
tration in | scalar divisions tration 
percentages mean corrected | calculated (in 
(weighed in) | !*t Gn B en percentages) 
0.1256 131.0 192° | 130.1 OE NOI 
0.1490 176.3 15:3 | 175.8 | 154.8 | 0. 1500 
0.2925 346.5 | 345 1 345.8 | 303.8 | 0.2920 
0.3208 314.9 | 315.6 | 375.3 333.3 | 0.3199 
0.4699 | 556.9 | 557.1 | 557.0 | 494.0 oy 0.4700 
0.5409 655.9 (684.9 | 655.4 | 871.4 | 0.5413 
0.7166 | 869.8 869.3 869.6 764.6 | 0.7166 
