630 
MR. H. B. DIXON ON CONDITIONS OF CHEMICAL CHANGE 
ments of pumice saturated with concentrated sulphuric acid. It was collected 
over mercury in glass cylinders which had been heated and filled while hot with hot 
mercury. On exploding 100 volumes of the gas in a wet eudiometer with 156*3 
volumes of oxygen a contraction of 50'17 volumes was observed, and on treating the 
residual gases with potash a further contraction of 100'00 volumes was observed. 
The oxygen was prepared by heating re-crystallized potassium chlorate in a piece of 
combustion tubing drawn out and bent, so that the drawn out end formed a delivery 
tube which dipped under the surface of mercury. On exploding 100 volumes of the 
gas with excess of hydrogen a contraction of 300'02 volumes was observed. 
The following experiments were conducted in McLeod’s form of gas analysis apparatus. 
A mixture of the two gases in the proportion of 2 volumes carbonic oxide to 1 
volume oxygen was kept in a glass cylinder over mercury in contact with a stick of 
potash. The apparatus, after dried air had been drawn through all its parts for twelve 
hours, was charged with hot mercury, and then specially dried in the following 
manner. The water in the glass jacket surrounding the eudiometer and barometer was 
kept for some hours at a temperature of 90°-95° C., while air, drawn through a nearly 
horizontal drying tube containing sulphuric acid, was passed by means of a bent glass 
tube dipping under the surface of the mercury in the trough, through the laboratory tube, 
eudiometer and barometer, to tire top of which an aspirator was attached. The mercury 
from the reservoir was run up several times into the hot tubes, so as to transfer to 
the glass any traces of moisture it might carry with it, and more dry air was drawn 
through the tubes after the mercury had been returned to the reservoir. By reversing 
the inclination of the sulphuric acid drying tube, the air in the eudiometer was expelled 
through it without disconnecting the laboratory tube. Finally the bent tube was 
removed, the air in the laboratory tube drawn over into the eudiometer, and the former, 
when completely filled with mercury, closed by its stopcock, The laboratory tube and 
eudiometer were then disconnected, the air in the latter expelled by running up 
the mercury until drops issued from the steel cap, when the stopcock was turned and 
the laboratory tube connected up again. The mixture of carbonic oxide and oxygen, 
prepared as above, was transferred from the glass cylinder to the laboratory tube, 
and thence was drawn into the eudiometer and placed under a pressure of 250 millims. 
of mercury, at a temperature of 17° C. On passing a spark from aLeyden-jar through 
the gases they did not ignite. Several powerful sparks were passed without result, 
and then the rapid succession of sparks from a Ruhmkoiiff’s coil was employed. At 
the first discharge the gases ignited and burnt slowly down the tube. The eudiometer 
was then further dried by drawing through it at 100° C. air which had been passed 
through two horizontal drying tubes freshly chai'ged with sulphuric acid. Some of the 
mixture used in the last experiment was passed into the eudiometer, and put under a 
pressure of 100 millims. (temp. 17°‘2 C.). Sparks from the Buhmkorff coil were passed 
through it without igniting it. The gases were tested under 150 millims. pressure 
with the same result. Under 200 millims. the gases did not ignite when a continuous 
