AND ON THE LAW OF PRESSURE OF OASES, ETC. 
213 
Ex'periments to determine the Relation o f Pressure and Volume at 
given Temperature. 
In order to test Boyle’s law one of the lateral branches C is connected to the air- 
pump and the other to the chamber in which the gas is contained. The pump is of 
the Toepler form, and is provided witlr a bulb containing phosphoric anhydride. No 
tap or contracted passage intervenes between the pump-head and B. A lateral 
channel communicates with a three-way tap, by which this side of the apparatus can 
be connected with the gas-generating vessel. The third way leads to a Idow-otl' 
under mercury more than a barometer-height below. 
The two sides of the apparatus are connected by a cross-tube which can be closed 
or opened by means of a tap. The plug of this tap is provided with a wide bore. 
When it is intended to read the zero, the tap is open. If desired, the mercury may be 
raised in the Toepler so as to prevent the penetration of gas into the pump-head. 
When pressures are to be observed, the tap of the cross-tube is closed, and a good 
vacuum is made on the pump side. No particular difficulty was experienced with the 
vacuum. In the use of the Toepler the mercury was allowed to flow out below, and 
was transferred at intervals to the movable reservoir. The latter was protected from 
atmospheric moisture by a chloride of calcium tube. When, after standing five or ten 
minutes, the mercury \vas put over, and, on impact, gave a hard metallic sound with 
inclusion of no more than a small speck of gas, the vacuum was nearly sufficient, and 
no further change could be detected at the manometer. The capacity of tlie pump- 
head was two or three times that of tlie remaining space to be exhausted. 
In the earlier experiments the gas-containing tulje, placed vertically, was graduated 
to 50 cub. centims. at intervals of 10 cub. ceutims. Prolonged below by more than a 
barometer-height of smaller tuljing, it terminated in a hose and mercury reservoir, 
the latter protected by , chloride of calcium. In order to get rid of most of the 
adherent moisture and carbonic anliydride, the tuljes on both sides of the apparatus 
were heated pretty strongly in a vacuous conditif)n. The first trial was with oxygen 
in the hope of at once obtaining a confirmation of Bohr’s anomaly ; l)ut not succeeding 
in this, I fell back upon nitrogen and hydrogen. With a vacuum on the pump side, 
readings of pressure were taken witli the mercury in tlie chamber at 0 and at 50 cub. 
centims., and the ratio of jDressures (about 2:1) was deduced. Wlien this had been 
repeated, some of the gas was allowed to escape by opening the cross-tap, the zero 
was again observed, and the vacuum re-established on the pump side. Another ratio 
of pressures could now’ be obtained, corresponding to tlie same (unknown) volumes as 
before, but to a different total pressure. 
In utilising the ratios of pressure tlius oljtained, it was of course necessary to 
consider how far the temperature could l)e assumed to be unchanged within each pair 
of pressures brought into comparison. The general temperature of the cellar was 
extremely uniform, and no difierence could be read upon a thermometer w'orth taking 
