90 Kansas Academy of Science. 



room-and-pillar method, or some of its modifications. In this 

 method the coal is broken down, not by the weight of the overly- 

 ing strata, but by the use of explosives; and in American mining 

 as now carried on explosives are used in very large quantities. A 

 few years ago one can of powder weighing twenty-five pounds 

 would frequently last two miners for a period of two weeks, and 

 some of the powder would often be spoiled by dampness before it 

 could be used. At the present time, in the fields of the Middle 

 West, two miners commonly use from five to seven cans of powder 

 in two weeks. The explosive used is almost entirely black blast- 

 ing-powder, the so-called safety powders having been introduced 

 to only a limited extent. 



It was thought that the gases given off by the combustion of 

 this powder might be contributory to some of the explosions which 

 have been recorded. It is now also well known that the dust of 

 some coals when suspended in air under certain conditions is ex- 

 plosive. The experiments then have been conducted principally 

 along two lines — an investigation of coal-dust and an investigation 

 of the gaseous combustion products of black blasting-powder. 



A third series of investigations, which may be regarded as ac- 

 cessory to the other two, was an investigation of the explosive 

 qualities of various gases in the form of simple mixtures with air, 

 and of complex mixtures of gases and air. The gases used were 

 such as are found in mines or in the combustion products of black 

 powder, and the tests have made possible the prediction of the 

 explosive or non-explosive quality of different mixtures which may 

 be found in the mine atmosphere. 



The behavior of gas mixtures has been tested under various con- 

 ditions. It has been found that the presence or absence of water 

 vapor makes a practically inappreciable difference. It has also 

 been found that increased pressure causes little, if any, change in 

 the explosiveness of the gases tested. In these experiments the 

 gases were ignited by a flame, by a heated platinum wire, and by 

 an electric spark. 



The experiments on the explosive qualities of coal-dust have in- 

 cluded a test of the dust of all coals which could be obtained, in 

 which the explosive or non-explosive character of the dust when 

 mixed with air was determined; and also the amount of dust which 

 it was necessary to su.spend in the air in order to make the mixture 

 explosive. Other substances besides coal-dust have also been tested. 

 These dusts were tested by placing them in a small box having a 

 rotating fan in the bottom. Ignition was made in most cases by 



