61G 
Prof. R. A. Lehfeldt on the Electrochemical 
consequence of changes of temperature. The gauge-tube 
should, for convenience, have either a rubber tube and 
stopper, or a tap to close it at the top when necessary. 
The tap L allows of communication with the atmosphere. 
The descending tube M is connected by a rubber joint with 
the gas-burette or measure-tube. 
The coulometer was, of course, thoroughly tested for 
leakage. 
The measure-tube was about 35 mm. in diameter, and 
contained 200 c.c. It was drawn out at the top to connect 
with M, and at the bottom to lead to a three-way tap. One 
side of the tap leads to a mercury reservoir, from which the 
mercury in the measure-tube is supplied before an experi- 
ment ; the other side of the tap allows the mercury, as it is 
displaced by gas, to flow out into a bottle. 
The measure-tube is surrounded by a glass water-jacket 
like a Liebig condenser, through which tap-water flows con- 
tinuously ; and the temperature is taken by a thermometer 
inserted at the top of the jacket. 
At first a graduated tube was used, but this was given up 
in favour of weighing the displaced mercury each time. 
The coulometer and measure-tube are supported by a 
retort-stand. 
The electrical connexions are shown in fig. 2. Current is 
taken from a battery of ten accumulators, each of about 
60 ampere-hours capacity. It is led through an ammeter A, 
to the three-part plug-key K by means of which the coulo- 
meter V may be cut out of circuit if desired. During the 
actual experiments the current flows through the coulometer 
to one terminal of S, the standard resistance, and from the 
other terminal to the rheostats E, R'. Of these, R is a dial 
