119 
This last improvement at the same time also greatly accelerates 
the exchange of heat between vessel and bath, so that already 
after 10 or 15 minutes the reading can take place. To prevent 
currents in the liquid during the measurement, the stirrer was 
always stopped a minute beforehand. 
8. Ad C. Evaporation of the liquid in the vessels. 
Only in more concentrated solutions is the error brought about 
by evaporation, greater than the error of measurement. If e.g. from 
2 cc. of a 0.1 N.-solution of C,H,Br, in C,H,Cl, 2 mgr. of C,H,CI, 
evaporates, this gives rise in our apparatus to an error of 1.6 scalar 
divisions. Greasing of the rim of the glass cover can, however, 
prevent such an evaporation. Another source of errors, however, 
still continues to exist, viz. distillation against the glass cover. This 
can often be observed already soon after the filling of the vessel; 
the liquid which is distilled moves between glass cover and vessel 
rim on account of surface tension, and attacks the vaseline. To prevent 
this it is to be recommended) in aqueous solutions to keep the 
temperature of the ‘‘Temperierbad” always some degrees lower than 
that of the room; in an investigation of more volatile liquids this 
is, however, not sufficient. 
9. It is, however, possible, to avoid this source of error entirely 
by using for the closure of the vessel, instead of glass plates, massive 
closing bodies, which occupy the whole vapour space. For this pur- 
pose brass blocks were constructed provided with a flat rim, which 
fit very tightly in the vessel, and leave only a space of + 2 ce. 
for the liquid. This is then conveyed to the vessel by the aid of a 
pipette of 2 cc. capacity, provided with a long capillary passed 
through a hole bored through the closing block. After the filling 
the bored hole is closed by a copper ground-in needle. Greasing 
of the rim of the vessel is now unnecessary ; no evaporation takes 
place through the remaining capillary slits. 
10. Ad D. The influence of the water absorption. 
Dry, organic liquids absorb water vapour from the atmosphere 
exceedingly rapidly. On account of the great difference in index 
of refraction between water and those substances, added to the 
sensitiveness of the method of measurement, however, the presence 
of exceedingly small quantities of water causes already errors in the 
1) Hirscu, Fermentforschung 1, 38 (1914). 
