IN GASES : HYDROGEN, CARBONIC OXIDE, AND OXYGEN. 
625 
diminishes the error due to residual air. The heights of the mercury in the eudio¬ 
meter and barometer are read off by a cathetometer. The whole apparatus stands on 
a stone floor in a cellar underground. 
The platinum wires are sealed into the eudiometer close to the shoulder, and are 
passed through two small glass prominences, over each of which an india-rubber tube 
surrounding the wire is stretched so as to prevent contact between tire wire and the 
water in the jacket. By this device a spark can be passed between the wires without 
lowering the water in the jacket. The lower ends of the eudiometer and barometer 
are not contracted. They are fastened gas-tight into steel blocks by a collar and nut 
compressing three or four india-rubber rings. The details of these junctions and of 
the 3-way steel cock are given in the diagrams (Plate 42.) By this arrangement the 
eudiometer and barometer can easily be removed and cleaned out with a long brush. 
I have found the steel caps joining the eudiometer and laboratory tube to answer 
their purpose most admirably. In eight years’ work I have never known an experi¬ 
ment to be lost on account of any failure of this joint. 
The readings of the instrument are made by artificial light. On the further side of 
the jacket a screen, half of translucent paper and half of black paper, with their line of 
demarcation horizontal, was made to slide up and down close to the window. 
Behind this screen and moving with it an argand burner, connected by a flexible 
tube with the gas supply, is adjusted ; with this artificial illumination more concordant 
readings are obtained than with variable daylight, and the experiments can be carried 
on at all hours. 
Repetition of Bunsen’s experiment. 
I commenced by repeating Bunsen’s experiments with carbonic oxide and electro¬ 
lytic gas. The gases were exploded over mercury in a wet eudiometer, and the 
calculations made according to the directions in Bunsen’s “ Gasometry.” In the 
following table the results of this first series of experiments are given side by side 
with Bunsen’s results, and expressed in a similar manner for the purpose of com¬ 
parison. The explosions were made under pressures varying from 200 to 300 millims. 
of mercury, and between the temperatures of 15° and 17° C. 
4 L 
MDCCCLXXX1V. 
