910 THE COLLIERY GUARDIAN Max 11, 1917. along the rib, and in some instances to avoid the use of powder entirely because the pillars are more or less shattered by the force of the explosives. Rock and • coal may be so weakened by jointing or cleats that the pillars offer little support. Moreover, the action of the atmosphere and moisture, particularly upon a deposit jointed as described, may greatly weaken the pillar. Soluble minerals in the pillars may be dis- solved by the mine water or the moisture in the air and the pillar thus weakened. Pyrites and other minerals may be oxidised, and a deterioration of the pillar will follow. It has been suggested by some that the loss of the included gas in coal beds tends to reduce the strength of the coal. The hydration or the dehydration of minerals may result in the weakening of pillars. The terms “ rashing,” “ slacking,” and slabbing ” have been applied to the process of weakening of pillars by the gradual dropping of material from the ribs, due in part to the action of moisture, oxygen, or pressure, or a combination of these agents. In mines operating in soluble minerals the preservation of pillars may be difficult owing to the flow of water in the mine or the1 moisture in the air. It may become necessary in mines of all types when, pillars deteriorate to protect important pillars by a coating of cement or concrete. Strength tests have been made upon coal and other minerals in order to determine how serviceable they will prove when left in pillars, and in order to esti- mate in advance of the opening of a mine in a new field the minimum size of pillar which may be left in safety for the protection of the mine openings them- selves, and of objects on the surface. Numerous tests have been made upon rocks used for building purposes, and the data thus secured are of service in determining the size of the pillars to be left in such rock. But more commonly the pillars left in mines are not composed of materials used for building- purposes, but rather of coal, ores of the various metals, and rock mineralised more or less with substances which are not permitted in structural materials. Moreover, the natural structural materials used are generally a selected product. Underground the pillar is frequently made up of the weakest portion of the deposit. Tests upon pillar materials are often of doubtful service, for, as a rule, they indicate the maximum load which can be borne by a unit of the mineral, and one that is often a selected unit. A coal bed, for instance, is composed of layers of varying hardness, and frequently it contains streaks of mother coal that would not be included in a sample tested for crushing strength. Compression tests of Illinois coal carried out in the Laboratory of Applied Mechanics, University of Illinois, showed the maximum load to vary between 1,000 and 2,170 lb. per sq. in. • Other tests, made by the H. C. Frick Coal Company upon samples of coal from the Pittsburg seam, show-the strength when com- pression is parallel to the cleavage and also when it is at right angles to it, viz., 3,170 to 3,4301b. per sq. in. in the former case, and 2,970 to 3,0501b. per sq. in. in the latter. A series of tests was made on 416 samples of Pennsylvania anthracite by a com- mittee from the Scranton Engineers’ Club. The samples were uniformly 2 in. square, but were of three different heights, namely—1, 2, and 4 in. The results are given in pounds avoirdupois per square inch of horizontal area, summary : — as presented in the following Grand average as per sq. in. Sample. First crack. 3,022 2,025 1,875 4,996 3,343 3,413 3,001 788 1,440 1,124 1,<»99 988 conclusions were Middle Field Maximum load. .. 6,421 .. 4,087 .. 2,854 .. 7,417 3,857 .. 3,821 .. 8,631 .. 3,499 .. 2,447 .. 3,814 .. 2,377 .. 1,809 Southern Field Height of sample. In. C 1 ... 2 ... t 4 ... C 1 ... Eastern Middle Field ... < 2 L 4 ... f 1 ... Western Middle Field... 2 4 ... 1. ... 2 ... 4 ... From these data, the following drawn:—“ That the. squeezing strength of a mine pillar of anthracite whose width is twice its height is about 3,000 lb. to the sq. in., and the crushing strength about 6,0001b. per sq. in., or, approximately twice as much. And, in general, other things being equal, the crushing strength of mine pillars would vary'inversely as the square root of the thickness of the bed. “ The same general rule apparently holds true also for the squeezing strength in all cases in which the height of the pillar is less than the width. In tall pillars, having a height greater than their width, the squeezing strength apparently remains nearly constant while the crushing strength continues to diminish with height according to the foregoing rule.” Subsequently additional tests were made at Lehigh University on samples of anthracite and of bituminous coal; 45 anthracite specimens were tested, but there seems to have been no uniformity in the amount of compression of the specimens taken as a whole or between the specimens from the same seam. The results of the tests upon 12 bituminous specimens were more uniform. The crushing strength per square inch ranged from 584 to 1,5831b., but nine ranged from 1,000 to 1,5381b. All of the bituminous specimens were taken from the Pittsburg seam. Additional data on the crushing strength of anthracite coal secured by Bunting showed the crushing strength to vary from 1,405 to 5,1131b. per sq. in., and the rela- tion between prism strength and cube strength between 0-71 and 1*63. The crushing strength of some British coals was measured and reported by Prof. Henry Louis (Trans. Inst. Min. Engin., vol. 28, p. 319, 1904). McNair, in discussing the conditions of deep mining in the Lake Superior district, refers to the crushing strength of the trap rock left in pillars as 1,200 tons per sq. ft. Richardson (Journ. Chem. Met and Min. Soc. of S. Africa, Mar., 1907) gives a table of the compressive strength of quartzite cubes taken from the depths of from 1,000 to 3,500 ft. in Rand mines. The first frac- tures appeared in the specimens under a pressure of 1,945 to 6,804 lb. per sq. in. The crushing strengths of these specimens were 8,054 and 9,0291b. per sq. in. respectively. Extent and Dip of Deposit.—The problem of surface support is naturally different in the case of a deposit which underlies an area of great lateral extent from that of support when the lateral extent is small. When the deposit underlies a small area, the geological structure of that area may be worked out-fairly accu- rately, and precautions may be taken to protect impor- tant structures on the surface. The dip and the position of the deposit may greatly modify the neces- sity for and the general policy of surface support. Uniformity of Mineral Deposit. — If there is fair uniformity in thickness, structure, quality, and depth over a large area, a systematic plan of support may be adopted, including, for example, pillars of uniform size at regular intervals, or a complete removal'of the deposit with or without filling. If there is not regu- larity as to these conditions, it becomes more difficult to employ a system of support or of working which will be economical, and at the same time provide sup- port for the surface. Notable examples of such con- ditions may be found in some of the coal fields of Illinois, where rolls, horsebacks, and faults compli- cate mining, and in some of the lead and zinc fields of the Mississippi Valley, where pillars of barren rock are left in the mines, and the rich portion of the deposits is mined out as completely as possible under such conditions. The pillars as a rule are neither uniform in size nor uniformly spaced. While such irregularities in the mineral deposit interfere to a degree with systematic working, yet they at times assist materially in preventing or checking extensive underground movements or subsidence. (To be continued.) Notes from the Coal Fields. [Local Correspondence.] South Wales and Monmouthshire. Alleged Waste of Small Coal—Shortage of Shipping and Idle Collieries — Engine House Fire — Ministers as Miners—Unemployment in the Coal Field—Pitwood. In answer to the contention which was raised at the Miners’ Federation annual meeting in Cardiff embodying an allegation' as to waste of small coal through stowing underground, a reply has been forthcoming from several directions. Amongst those is the statement of Mr. Jacob (general manager of the Ferndale Collieries), who points out that the only small coal left behind in the workings is so mixed with rubbish as to be practically use- less. He states that much more small coal is now brought out than was formerly the case. At present a far larger percentage of the output, as compared with a year ago, is small. At one time the percentage was 15 to 18 per cent., whereas now it is nearer 30 per cent. In earlier years there was no market for small coal, and thousands of tons were thrown away. But at present there is a demand for it. He adds that where the proportion of small is high, an allowance is made to the collier for what he fills, and that a sum of Is. per ton or more is allowed for small coal. The Swansea deputation which waited upon the Coal Controller in reference to the shortage of trucks, as well as shipping, consisted of Mr. Evan Williams (Llangen- nech), Maj. Harries, Mr. Farr, and Mr. R. L. Sails; and they impressed upon that gentleman the urgency of the position, pointing out that coal could not be despatched to France and Italy, where there was extreme need ; and the same day the acting-president (Mr. Winstone) and the secretary (Mr. T. Richards) of the Miners’ Federation also saw the Controller, urging him to take remedial action, and pointing out how very seriously the workmen suffer, especially in the anthracite area, owing to compulsory stoppages due to lack of tonnage. The anthracite miners met on Saturday, and the report of a deputation to the Coal Board was submitted, mem- bers of that deputation having presented their views as to more equal shipments to local ports. The report was accepted ; and the meeting passed also a resolution desiring the miners’ executive to call the attention of the Food Controller to the inadequacy of the bread allowance, especially to the mining community. It was also decided to revise the payment of the Labour representatives who serve on the local council. The Avon Valley miners met on Saturday, and a report was presented by their agent (Mr. Jenkins) as to negotia- tions between the Federation executive and the Coal Con- troller upon better shipping facilities, it being stated that as a result of that consultation greater attention would in future be given to that portion of the coal field. Fire broke out on Saturday in the engine house of the South pit at Oakdale Colliery, in the Sirhowy Valley, and as a strong wind was blowing at the time, the outbreak was very difficult to deal with. The roof was ignited by sparks from the ground floor, and there was risk that slates would fall into the machinery. The colliery fire brigade, with the brigade from Blackwood, and that from Pontypool, overcame the outbreak in about two hours. As the machinery escaped damage,' there will be no stoppage of work. The Western Miners’ Association passed a resolution adverse to the working of ministers in the mines, it being stated that they are exempted from military service by their position, but that some had entered collieries although a large number of regular miners were out of work or had only half-time. The resolution “ protested against the action of the ministers of the Gospel and others who, themselves exempted from military service, have entered the mines to replace young men for the Army, when a large number of miners are out of employment.” The extent of unemployment in the South Wales coal field varies considerably in different areas. It is chiefly in the western districts that idleness has become compul- sory ; for in the eastern part of the coal field it is to be . noted that Monmouthshire men are able to work regu- larly ; and there have been no stoppages in the Aberdare and Rhondda Valleys neighbourhood; whilst in the mid- Glamorgan district only two collieries have suffered, and these two to the extent of only two days each. In the Rhymney Valley there has been regular work except in the case of the Elliot Collieries, which stopped through break- down of fan. It was announced a week or two back that Mr. J. Dyer Lewis will be chairman of the Pitwood Committee appointed by the Controller of Mines for the South Wales district. The coal owners’ representatives include the chairman of their association (Mr. Nicholas), with Mr. Evan Williams, Mr. North Lewis, Mr. E. M. Hann, Mr. W. Stewart, and Mr. Gibson, their secretary. There will also be representatives of the owners of plantations, a representative of the Admiralty, a technical assistant to the chairman, and a representative of the Director of Timber Supplies. Arrangements will be made for distri- buting pitwood supplies to the different collieries after such enquiries have been made as enable the committee to forecast, and therefore adjust, the requirements of each ; and they will keep in touch with the Director of Timber Supplies, so that regular transport of the right kinds of pitwood may be secured. In every district there are to be storage depots for accumulation of supplies ; but as yet the position of the South Wales depots has not been fixed. There will be co-operation with the Railway Executive Committee so as to ensure facilities for the transport of timber; and the whole combination will be so worked as to minimise expenditure of time and labour in obtaining supplies. The directors of the South Wales’ Colliery Owners’ Pit- wood Association met on Tuesday, the members including Mr. B. Nicholas (chairman of the Coal Owners’ Associa- tion), who represents Tirpentwys Colliery Limited, Mr. W. R. Hann (Powell Duffryn), Mr. J. Miles (United National), Mr. Cooke (Guest-Keen), Mr. T. Evans (Ocean), Mr. W. North Lewis (Insoles), Mr. Evan Williams (Glyndwr, Pontardulais), Mr. W. H. Mewton (Locket’s Merthyr Colliery Company), Mr. T. H. Deakin (Park End, Lydney), Mr. Stephen Reid (Messrs. Evan and Reid, Cardiff), Mr. William Stewart (Brodawel, Caerleon), Mr. Sidney Fifoot (Great Western Colliery Company), Mr. F. B. Saunders (Rhymney Iron Company), Mr. A. S. Tallis (Tredegar Iron and Coal Company), Mr. Rhys Davies (Evans and Bevan, Neath). The new association is a development of the organisation which was formed some time ago to further the use of home-grown timber, and effect economy in the use of shipping by limiting the use of imported pitwood. The response of the coal owners generally was very satisfac- tory, and there is already a membership which represents more than 90 colliery companies, having an output of over 40,000,000 tons a year. The meeting on Tuesday appointed Mr. Nicholas as chairman, Mr. Mewton as vice-chairman, Mr. F. A. Gibson secretary, Mr. Kenshole solicitor, and Messrs. J. C. Kirk and Sons auditors. It is understood that purchase has already been made of plantations both in Cardigan and Monmouthshire, and that over 100 men are now engaged in felling the trees. Motor lorries will be used for carrying the cut timber; but as yet the home supplies are in no way near the requirements, which are estimated to amount to at least 12,000 tons per week; so that the association will have to deal with pitwood mer- chants as well as-conduct independent operations. The general licence permitting importation of pitwood is to be revoked from May 15, and afterwards it will, be necessary to obtain special licences, although any consign- ment which was on the way to an importer before May 15 will continue to have the privilege of the general licence. So far as South Wales is concerned, a very large part of the imports come through < Lysberg Limited, who have dealt with the Admiralty collieries pitwood since a period shortly after commencement of the war; and Messrs. Thomas and Company also have dealt with a large propor- tion, other firms, of course, being engaged with outside . trade. The anticipation is that whilst collieries on the Admiralty list will not experience any hindrance in getting supplies, those who are not in this fortunate position may find in the new arrangement as to licence one fresh source of difficulty. Circumstances, however, may become more favourable through the operation of the Pitwood Associa- tion previously described. Several colliery workmen have been fined <£1 each at Bridgend for travelling on the main haulage road when the machinery was in motion; and the solicitor who prose- cuted on behalf of the Ton Philip Rhondda Colliery Com- pany, stated that the men exposed themselves to great danger, and the company were anxious. to put a stop to the practice. The resumed conference of miners’ delegates in Cardiff on Tuesday, further discussed the question of “ combing out ” colliery workmen for the Army. More than 151,000 members were represented by about 200 delegates. Mr. J. Winstone (acting-president of the Federation) once more set out the facts of the situation, and also brought up the recommendation of the Miners’ Federation of Great Britain, which the South Wales executive desired the conference to accept — namely, that the Government’s scheme should be supported. By a majority vote, the conference decided to accept the recommendation of the Miners’ Federation of Great Britain and their executive. A resolution was passed expressing the opinion that the minimum of dislocation and of injury to the trade could be obtained, and individual injustice avoided, only by recruit- ing, as far as possible, from those who have gone to the mines from other trades since August 1914. The matter was remitted to the executive committee. Northumberland and Durham. Durham County Sailors' Day—New Magistrates—Flower Day—Homes for Aged Miners. The Dowager Lady Londonderry has addressed a special appeal to those colliery companies and others in the county of Durham which have not yet subscribed to Durham County Sailors’ Day. She states that nearly <£5,000 has been collected, and adds : “ We are endeavouring to keep the money for the county of Durham, and eventually, if possible, to arrange a scheme with Northumberland to get a training ship for the north-east coast to educate the orphans of those who have lost their lives belonging to the Navy, mercantile marine, mine sweepers, and trawlers.” In addition to those gentlemen mentioned last week as having been appointed Durham county magistrates, Mr. John Willan, of Shincliffe, Mr. Eli Cook, of Pelton, and Mr. J. Bell, of Ferryhill, have been similarly honoured. Mr. Willan, who is senior magistrate for Durham City, was formerly vice-chairman and director of the Durham Gas Company, and is now a director of the Tudhoe and Spennymoor gas undertaking. Mr. Cook has rendered good service on the executive of the Durham Miners’ Association, and is chairman of the Chester-le-Street Board of Guardians. Mr. Bell is checkweighman at the Dean and Chapter Colliery, representative of Ferry hill on the Durham County Council, and has been a member of tfie Durham Miners’ Association executive. The committee of the Durham Aged Mine Workers’ Homes Association has fixed Saturday, July 14, as the annual flower day in aid of the Homes funds. Last year about <£1,000 was-collected, and in the past three years the sum raised has been <£1,785 4s. 4d.