586 EVENING DISCOURSES 
workings of the mine, such as occurred in 1905-12, need no longer be 
feared. 
The study of the causes of mine accidents, whether they be due to falls 
of roof, to mishaps during haulage or to explosions, and the devising of 
remedies, are not in themselves sufficient to secure the increased safety of 
the mine worker that we all desire. Often enough, the application of a 
remedy against an accident rests with the miner. It is necessary, therefore, 
to instruct the miner, who has shown himself most willing to be instructed, 
as to the reasons for the measures for safety, sometimes arduous, that he is 
called upon to perform, and as to the risks he runs if he neglects them. 
For this reason the educational work of the Safety in Mines Research Board 
ranks equal in importance with its experimental work. 
EXPERIMENTS. 
Experiment I.—Experiments on propagation of flame in methane-air mixtures. 
Mixtures.—10 per cent. methane-air mixtures. Measurements of the 
required amounts of air and methane are made by means of rotameters ; 
after passing through a mixing apparatus the mixture is passed into the 
explosion tube. 
Tube.—Horizontal glass, 19°5 ft. long, 2 in. diameter. 
Ignition.—By single break spark between electrodes (4 mm. gap). 
Experiment (a). Propagation from open to closed end of tube.—Mixture 
ignited by spark at electrodes 6 cm. from the open end of tube. 
Propagation showing uniform movement and subsequent vibratory phase. 
Experiment (b). Propagation from closed to open end of tube.—Mixture 
ignited by spark electrodes 2:5 cm. from the closed end of tube. 
Higher mean speed of propagation with vibrations. 
Experiment II.—Experiments on the inflammability of coal dust and the effect 
of stone dust thereon. 
Test I.—Violent inflammation of a typical coal dust. 
Test II.—Suppression of inflammation by using an adequate proportion 
of stone dust. 
Typical coal-dust . ; : . 45 per cent. 
Fuller’s earth ; : i UBIGIUT SG Ee 
Test III.—Partial suppression of inflammation by using less than the 
statutory amount of stone dust. 
Typical coal dust . : 4 . 65 per cent. 
Fuller’s earth ! . f TOtyED BOL 
Experiment III.—Experiments on the ignition of methane in air by a heated 
surface and the effect of iodine on the ignition temperature. 
Notr.—The late Professor H. B. Dixon showed that traces of iodine 
had an inhibiting effect on the ignitions of methane air mixtures. 
A jet of methane is passed on to a heated alundum surface, maintained at 
a temperature sufficient to ignite the methane in the surrounding air stream. 
When the air stream is passed over crystals of iodine at laboratory tempera- 
ture (and thus contains 0°03 to 0°04 per cent. of iodine vapour) ignition 
does not occur owing to the inhibiting action of the iodine. It is proposed 
to erect two similar heated surfaces, cylindrical in shape. One will be 
maintained at a temperature just sufficient to ignite the jet of methane in 
air. ‘The second apparatus will be used for experiments with air contain- 
ing iodine to show that a higher temperature is necessary for ignition 
under these conditions. 
