Prof. H. Louis (Durham College of Science) asked whether the contractors had changed their opinion with reference to boring the holes through the boulder-clay and into the solid freestone. Many engineers who saw the process at Washington, could not imagine any valid reason for freezing this clay; but the contractors stated they had experienced considerable trouble in freezing strata containing boulder-clay in Germany. He (Prof. Louis) imagined that these were only lenticles of clay lying in the quicksands, and did not compare with the immense beds of boulder-clay found in this country. Mr. J. K. GUTHRIE (Preston) said that he had sunk a shaft (14) feet in diameter) through boulder-clay in the ordinary way, putting in cribs, etc., and no trouble whatever had been experienced. Mr. A. GOBERT (Brussels) wrote that he noted with pleasure that the Centigrade thermomenter had been adopted for observations of the temperature of the brine and cooling-water, and he would suggest that British mining engineers should also adopt the Continental calorie as the unit of heat, as by so doing it would be much easier to compare results obtained on both sides of the Channel. The description of the permanent lining used at Washington was interesting, but he would like to have some indication as regards prices. The question of cost might also be usefully discussed for all parts of the process of walling. He might point out that very important sinkings by the freezing process were contemplated in Belgium, and it was expected that the soil of Brussels would be frozen for the line of railway to be made between the Nord and Midi railway-stations. The government had consulted the writer, and he had given them a complete report upon the subject. Mr. F. R. SIMPSON (Ryton) said that he had read Mr. Ford's paper with interest, not only because he had seen the process in operation at Washington, but he had recently made himself acquainted with what was being done by this method on the Continent. There, it was recognized as one of the regular methods of sinking through sands, either at the surface or at great depths. At one colliery, a shaft had been sunk by this method to a depth of nearly 800 feet. Difficulties had been ex perienced in boring vertical holes, and from the breaking of the pipes, but in every case these difficulties had been overcome, and he had not heard of any case in which there had been failure to complete the shaft in the contracted time. The members were indebted to the Washington Coal Company, Limited, for showing what could be accomplished by this method of sinking, and there could be no doubt that the sands. met with in the east of Durham, could be successfully sunk through with the assistance of the freezing method. He moved that a vote of thanks be accorded to Mr. Ford for his valuable paper. Mr. J. G. WEEKS (Bedlington), in seconding the vote of thanks, said that the recent excursion of the members to Washington colliery had been most successful. The vote of thanks was cordially approved. Mr. MARK FORD, in acknowledging the vote of thanks, said that a slight feeder of water was coming through the walling. The addition of caustic soda to the mixing water prevented the cement from freezing, and allowed time for its setting. Before sinking the second pit, he wrote to the contractors as to whether they still considered it necessary to freeze the boulderclay; they maintained their previous opinion, and stated that they absolutely refused to take any responsibility as to the sinking of the shaft unless the boulder-clay was frozen. Mr. JAMES STEWART's paper on "The Valuation of Gascoals" was read as follows: THE VALUATION OF GAS-COALS. BY JAMES STEWART, EDITOR OF THE GAS WORLD. The valuation of coal for gas-making purposes is peculiar in that no ordinary laboratory-method of analysis, such as serves to value most technical materials, will suffice. It is not like lime, for instance, the value of which, either for gas-purification or as a cement, can be inferred from its chemical analysis; nor like a lubricant, the utility of which can be estimated from its behaviour when exposed to certain physical and chemical tests. An ultimate analysis, revealing the elementary constituents of the coal, may perhaps show its fitness or otherwise for gas-making, but it is no trustworthy guide as to its value for that purpose. And a proximate analysis, showing the respective amounts of volatile and fixed products when the coal is subjected to destructive distillation, is of little, if any, greater utility. The actual value of a gas-coal can only be ascertained by imitating the treatment which the coal will receive in the gas-works, and thus producing from it the gas and bye-products for which it is valued. The scale on which the process is carried out may vary considerably, according to the resources at command and the preferences of the operator. The minimum, however, is fixed, in that at least sufficient gas must be produced to enable its illuminating power to be determined by the Bunsen photometer; which means that not less than 1 pound of coal, yielding, say, 5 cubic feet of gas, must be carbonized. Ordinarily the laboratory apparatus is of little more than twice this minimum, and carbonizes at one operation 2 pounds of coal, which is practically 0·001 ton. The experimental plant of a modern gas-works is generally on a much larger scale, being arranged to carbonize 1, 2, 3 or 4 cwts. of coal at once; and in a few cases it is on a scale of still greater magnitude, constituting, in fact, a small gas-works in itself. |