It has, however, been deemed advisable to give practical proof to those who would have to use it, that roburite possesses all the high qualities claimed for it, and hence separate and independent trials have been arranged in such representative collieries as the Wharncliffe Silkstone, near Sheffield, Monk Bretton, near Barnsley, and, further north, in the Durham coal field, at Lord Londonderry’s Seaham and Silksworth collieries.  Mr. G.B.  Walker, resident manager of the Wharncliffe Colliery Company, had gone to Germany as an independent observer—­provided with a letter of introduction from the Under Secretary of State for Foreign Affairs—­and had seen the director of the government mines at Saarbruck, who gave it as his opinion that, so far as his experience had gone, the new explosive was a most valuable invention.  Mr. Walker was so impressed with the great advantages of roburite that he desired to introduce it into his own colliery, where he gladly arranged with the company to make the first coal mining experiments in this country.  These were recently carried out in the Parkgate seam of the Wharncliffe Silkstone colliery, under the personal superintendence of the inventor, Dr. Roth, and in the presence of a number of colliery managers and other practical men.

In all six shots were fired, five of which were for the purpose of winning coal, while the sixth was expressly arranged as a “blowout shot.”  The roburite—­which resembles nothing so much as a common yellow sugar—­is packed in cartridges of about 41/2 in. in length and 11/2 in. in diameter, each containing about 65 grammes (one-seventh of a pound) inclosed in a waterproof envelope.  By dividing a cartridge, any desired strength of charge can be obtained.  The first shot had a charge of 90 grammes (one-fifth of a pound) placed in a hole drilled to a depth of about 4 ft. 6 in., and 13/4 in. in diameter.  All the safety lamps were carefully covered, so that complete darkness was produced, but there was no visible sign of an explosion in the shape of flame—­not even a spark—­only the dull, heavy report and the noise made by the displaced coal.  A large quantity of coal was brought down, but it was considered by most of the practical men present to be rather too much broken.  The second shot was fired with a single cartridge of 65 grammes, and this gave the same remarkable results as regards absence of flame, and, in each case, there were no noxious fumes perceivable, even the moment after the shot was fired.  This reduced charge gave excellent results as regards coal winning, and one of the subsequent shots, with the same weight of roburite, produced from 10 to 11 tons of coal in almost a solid mass.

It has been found that a fertile cause of accidents in coal mines is insufficient tamping, or “stemming,” as it is called in Yorkshire.  Therefore a hole was bored into a strong wall of coal, and a charge of 45 grammes inserted, and very slightly tamped, with the view of producing a flame if such were possible.  This “blowout” shot is so termed from the fact of its being easier for the explosion to blow out the tamping, like the shot from a gun, than to split or displace the coal.  The result was most successful, as there was no flash to relieve the utter darkness.