442 
with pressure of admitted air so that the sulphuric acid manometer 
shows but a slight difference in pressure. The compensation pressure 
is read off on the closed mercury manometer L which is furnished 
with a plate glass scale thus rendering possible a reading to 0.1 m.m. 
E is a long india-rubber tube rendering it possible to place the 
tensimeter in a vertical position inside or outside the thermostat T. 
An experiment was carried out as follows: Through the at first 
open tube D measured portions of Br and I were successively intro- 
duced with a long funnel into A; the quantities introduced were 
determined by weighing the tensimeter. A capillary tube was then 
sealed to D, and the little flask A was heated until the mixture 
was wholly fused or nearly so. Then the bulb of the thermometer 
was slowly cooled to — 79° (in the Dewar glass N) and the tensi- 
meter placed horizontally thus causing the sulphuric acid to ran 
into the bulbs C. Halogen vapour was drawn out with a water air- 
pump and then the capillary tube D connected with P. Q is a 
long lime tube for the protection of the oil-pump R. The whole 
apparatus was now carefully evacuated, the capillary was fused off 
at D and the tensimeter, after a gradual warming, introduced into 
the thermostat T. In the mean time so much air was admitted into 
the right half of the apparatus that the sulphuric acid manometer 
showed but a slight difference in pressure. This was done by means 
of a three-way cock G. In the tube H was contained air which can 
be replenished by opening the pinchcock K; a considerable narrowing 
at | facilitated the regulating. Moreover some modifications in the com- 
pensation pressure could be introduced by the displacement of mercury 
in the gasburettes combination MM. The whole apparatus reminds 
somewhat of the one employed by Mrgerum Trerwoer’). The measu- 
rement of the pressure is here, however, capable of greater accuracy, 
the pressure compensation is easier whilst the complication near 
A (a loosely placed in vessel for the reaction mixture) has been 
omitted as it proved to be superfluous; not once has a tensimeter 
been broken there. 
Reading off the sulphuric acid tensimeter was possible through 
the pane of glass O of the thermostat: 
The density of the acid employed was determined with the sp. gr. 
bottle at one temperature only ; at the other temperatures the table 
of Domke ®) was consulted. The thermostat was furnished with a 
toluene-regulator, a normal thermometer divided to 0°.1 (read off 
with a magnifying glass) and a constant level arrangement. We 
“1 Diss. pag. 37; pagi: 
*) Z. f. anorg. Chem. 53, 125 (1905). 
