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MR. H. B. DIXON OX CONDITIONS OF CHEMICAL CHANGE 
coefficient of affinity was altered, more carbonic oxide and less hydrogen being burnt. 
When similar mixtures were exploded in tubes of different diameter, v. Meyer in 
most cases found that the coefficient of affinity was altered. In a large tube of 20 
millims. diameter more carbonic oxide and less hydrogen were burnt than in narrower 
tubes of 12 - 5 millims. and 5 '5 millims. diameter. With one mixture, however, v. 
Meyer found no alteration of the coefficient whether the explosion was made in the 
largest tube or the smallest. This change of affinity he attributed to the increased 
friction of the gases in the narrower tubes, which he says always tends to increase the 
relative affinity of hydrogen for oxygen. In most cases this increase of affinity is 
sufficient, according to v. Meyer, to cause a leap in the proportion of hydrogen to 
carbonic oxide burnt, but in a few cases, where the equilibrium is more stable, this 
increase of affinity does not suffice to alter the ratio of the gases burnt. 
In the summer of 1876, at the suggestion of Mr. Vernon Harcourt, I began 
experiments in the Christ Church laboratory to test the truth of Bunsen’s law. 
I was ignorant at the time of the paper Horstmann had published in a local journal" 
at Heidelberg in the spring of the same year. 
Description of the apparatus. 
The apparatus employed in the earlier experiments detailed in this paper was 
devised by Professor McLeod and erected by him in the Lee’s laboratory at Christ 
Church, Oxford. The construction of this instrument is too well known to require 
description. 
The later experiments were made in the laboratory of Balliol College with an 
apparatus devised by Professor F. D. Brown for measuring the tensions of saline 
solutions. The only alterations I found necessary to make were (1) the substitution 
of a eudiometer (with a bent capillary tube and steel cap) in place of the shorter 
tension-tube, (2) the adjustment of a movable shelf to two of the iron uprights to 
hold a mercury trough for the laboratory tube. 
A general view of this instrument and details of the connections are given in 
Plates 41 and 42. 
The framework of the instrument is very strongly constructed of iron, screwed up 
firmly together. The jacket surrounding the eudiometer is of copper, with a wooden 
casing. The jacket has a door near the bottom, and a movable plate at the top, both 
made of gun-metal. The windows are of plate glass. The liquid employed in the. 
jacket is water for temperatures below 100°, and a mixture of glycerin and water for 
higher temperatures. A screw-stirrer is made to revolve in the liquid. In an 
annular pipe, outside the jacket, and opening into it near the top and bottom, the 
liquid is heated and a continuous circulation maintained. Two thermometers 
graduated to tenths of degrees are placed at different heights in the jacket. The 
mean of their readings is taken as the temperature of the gas in the eudiometer. 
The barometer tube is surrounded with a water-jacket. An enlargement at the top 
* Verb, des Heidelb. naturf. med. Vei’eins, N.S., I., 3. 
