February 15, 1918. THE COLLIERY GUARDIAN. 327 In order to arrive at an estimate of the output and reserves of the semi-coking coals, a considerable amount of investigation must be undertaken; but it will be necessary to have adequate data on this point before launching schemes with large capital outlay. One thing is evident—that those semi-coking coals are not being used at present to the fullest economic and national advantage. Apart from the round coal, the quantity of small coal which is being consumed in boiler fires, without recovery of by-products, must amount to several thousand tons per day. There has been considerable public discussion on the Reconstruction Committee’s proposed super-power stations, and that subject is closely related to the points above mentioned. If it be admitted that a supply of coke for the blast furnaces is a necessity of the near future, the most economical method of pro- ducing that coke becomes a matter of supreme import- ance. A super-power station producing coke must be placed geographically in a convenient centre for sup- plies of suitable coal, for water for condensing and dross washing purposes, and for the sale of power, coke, and other products. These considerations point to the establishment of a station where coking coal is within reasonable distance, and where the coke can be disposed of to neighbouring blast furnaces. The information regarding the localities in which semi-coking coal may be found indicates that a super- power station to use these coals would require to be placed somewhere between Coatbridge and Shotts. The Reconstruction Committee point out, however, that a necessity for such a station is that the site should be upon an important waterway, and this con- sideration alone would almost certainly rule out any site in the district mentioned. A site adjacent to the River Clyde would comply with the conditions as to water, and would also be close to plentiful supplies of non-coking coal. The extra railway carriage involved in bringing semi-coking coal and distributing the coke to the furnaces would probably neutralise any benefit that would be obtained by erecting coke ovens at a centre so placed. The Reconstruction Committee further recommend that “ power available from surplus gas or waste heat should be turned into electrical energy on the spot in local plants which would feed into the main distri- bution system.”* This points to the establishment of smaller stations near the blast furnaces on the lines which have proved so successful in the Newcastle and north-east coast dis- trict. With these smaller stations the existing by-pro- duct plants attached to the blast furnaces could be utilised and extended where necessary. The surplus gases and waste heat from the ovens and furnaces could there be transformed into electrical energy on the most economical basis. Naturally, they would feed into the main power system of the district, and would be run in parallel with the main generating stations. As in the case of the north-east coast, they would be run— so that they each supply the maximum amount of energy possible—depending on the supply of waste heat or steam available—all regulating being done by the main power stations. The power company need instal no spare plant in any of the waste heat stations connected to its system, being able to meet any variation of load by means of its coal-fired stations, which also act as stand-by against any breakdown. Moreover, the power company, having a market for current many times greater than the output of any individual waste heat station, is able to run such stations continuously at their maximum output capacity, so utilising completely all the cur- rent that can be produced therein; whereas it is impossible to conceive the power requirements of an individual coke oven and colliery installation coin- ciding even approximately over 24 hours with the amount of gas or waste heat available.! By means of the proposed power stations, whatever form they may take, three primary objects will be secured, namely—economical production of electrical power; supply of coke for blast furnaces; and recovery of by-products at present going to waste. * “ Interim Report on Electric Power Supply in Great Britain,” p. 18. + Ibid., p. 27. More Coke Available.—In view of the continuing supply of sufficient quantities of gas coke in the Metropolitan area, the Controller of Coal Mines announces that arrange- ments have been completed by which consumers can obtain a quantity not exceeding five tons in any one case, in addi- tion to the supply authorised under their requisition or under a certificate in accordance with the terms of the Household Coal Distribution Order, 1917. Application must be made to the local coal overseer of the district in which the consumer resides. Coal Carbonisation.—A special course of lectures deal- ing with developments in the coal carbonisation industry has been arranged to be delivered in the Applied Science Department of the University of Sheffield. The course is intended chiefly for persons engaged in the gas or coking industries, but is open to all persons interested in the carbonisation of coal, whether students of the university or not. On the Mondays in March, commencing at 7 p.m., Mr. J. W. Lee, manager of the Hasland Coking Company Limited, will lecturk on “ Problems Connected with the Manufacture of Ammonia Liquor.” The first of the series will deal with plant, principles, capacities, etc. On the same Mondays, commencing at 8 p.m., Mr. M. Wynter Blyth, chief chemist at Messrs. Newton, Chambers and Company Limited, Sheffield, will lecture on “ Commer- cially Pure Benzene, Toluene, and Xylene, with Special Reference to Problems in Fractional Distillation.” On Mondays, April 8 and 15, commencing at 7 and 8 p.m., Mr. E. W. Smith, chief chemist of the Birmingham City Gas Department, will deliver four lectures on “ Recent Develop- ments in .Carbonising Practice.” The concluding lecture of the series will deal with internal and external producers, and their application to the heating of settings, with special reference to the classification of coke. The lectures are in groups of four, and students may join one group or all. THE STRENGTH OF PIT PROPS.* By F. L. Booth. In submitting the following tables of the results of tests of crushing strengths of various sizes of pit props, the author wishes it to be clearly understood that the tests were made in order to obtain practical data for a particular purpose, and it is not claimed that the results represent the strength of timber from what might be termed the scientific point of view. Owing to the growing scarcity of supplies of timber, and especially the difficulty in obtaining certain sizes, it became necessary to cut up large timber, and it was in order to ascertain the relative strength of this cut timber, as compared with round props, that the tests were made. The proposal was to quarter 6 in., 7 in., and 8 in. props, of which there was a good supply, and use these instead of 2| in., 3 in., and 3| in. props, and, as a result of the tests, it was possible to give general instructions to the timber yard officials as to what sub- stitutes could be sent to the pit in case of a shortage of any particular size. It is regretted that the only details available of the class of timber tested are those given in the tables, but, as already explained, the tests were practical, and no selection of timber was made except as to size. The timber was taken haphazard from the stacks, ready to go into the pit, the ends were roughly squared, and no particular care was taken in settling them in the press. The machine employed was an ordinary hydraulic ram press used for pressing-on wheels, crank pins, etc. The diameter of the ram is 12 in., and the pressure gauge used was a most reliable standard test gauge, with two independent gauges combined in one case, each pointer recording its own pressure ■ upon a separate scale, and acting as a check on the other. The graduations are in divisions of 2 J lb. per sq. in. • As the machine, as ordinarily used, could only take props up to 18 in. in length, the first set of tests were of props of this length (Tables I. and II.), as it was thought that these would give the necessary compari- son. The legs were afterwards lengthened, and a further series of tests were made on props 4| ft. long. It was felt that the differences in the four tables were so slight, and might be easily explained by the relatively few tests made, that the most likely way to eliminate or reduce any errors would be to add them together. It will be noticed in column 5 of Table V. that the strength per square inch decreases apparently as the size of the prop increases. Whether this is really so, the author is unable to say. It was decided for the practical purpose of the tests to take still further advantage of the law of averages, and work out a new figure column, 6, containing the average strength per square inch of all the props tested, and from this calculate the strength of the prop according to its diameter (column 7). With further reference to the apparently greater strength pel’ square inch of small timber, it must again be remembered that the sizes here given are not neces- sarily exact. While a 3 in. prop sent into the pit may be anything up to nearly 3| in., for the purpose of the tests the prop taken was as nearly as possible 3 in., not less, generally stiff, and in some cases almost J in. over this size. From this it is suggested that a little oversize on a small prop will have more effect than on a large prop, and this may account for the tests showing a greater strength per square inch for small timber. The areas given for the quartered props are a quarter of the area of a round prop of the size indi- cated, and no allowance is made for the saw cut. Neglecting this point, it will be seen that the cut prop is 23 per cent, weaker than a round whole prop of the same area (1-77 - 1-36). From these figures it was possible to say that a 7 in. prop quartered could be used in place of a 3 in. round prop in case of scarcity of that size. This is quite borne out in practice, and cut props selected according to this standard have given every satisfaction. Conclusions. It may be of interest to give the author’s general conclusions from the information he gained in making the tests. These opinions were primarily for the assistance of the officials at the colliery, but might form the basis of discussion by members of the insti- tute. In considering the following conclusions, due regard must be had to the limited number and range of the tests : — (1) The strength of a round prop is independent of its length within the limit of 4 ft. 6 in. (range of tests). (2) The strength of a round prop per square inch of area is independent of its total area. (3) A quartered prop is 23 per cent, weaker than a round prop of equal sectional area. (4) Sun cracks (reasonable), if straight and parallel to the length of the prop, do not appreci- ably affect the strength of the prop. (5) Sun cracks, if diagonal (say, to the extent of quarter of the circumference in 2 ft.), greatly reduce (by nearly 50 per cent.) the strength of the quar- tered props, which should on no account be cut from timber of this nature. Test of Home-Grown (Scotland) Timber. Table VI. contains the result of a number of tests of home-grown timber used unseasoned. Table VII. shows the result of pieces cut from the same timber as used in Table VI., after being dried for four months in a boiler house. These tests (limited in number, it is admitted) show that the seasoned timber increased 40 per cent, in strength after being dried for four months. They also indicate that home grown timber (seasoned) is stronger than foreign timber (1*76 — 2-00 = 13-6 per cent.). * Paper read before the North of England Institute of Mining and Mechanical Engineers on February 9. Table I.—Average of a Number of Tests of Crushing Strength of Baltic Timber ; Length, 18 in. Description of prop. No. of pieces tested. Area of prop. Total load on prop. Load per sq. in. Average. In. Sq. in. Tons. Tons. Tons. 24, round ... 16 ... . 4’90 . .. 8’88 .. . 1’81) 3 „ ... 16 ... . 7’07 . .. 12’34 .. . 1’74 I ... 1’79 34 „ 16 ... 9’62 . .. 18’55 .. . 1’91 C 4 „ ... 16 ... 12’56 . .. 21’95 .. . 1’70 J 6, quartered [ 16 ... . 7’07 . .. 10’79 .. . 1’52) 7 16 ... 9’62 . .. 14’38 .. . 1'49? ... 1’43 8 „ ... 16 ... 12’56 .. .. 15’6: .. . 1’27) Table II.—Average of a Number of Tests of Crushing Strength of Russian Timber, Seasoned ; Length, 18 in Description of prop. No. of Area pieces of tested, prop. Total load on prop. Load per sq. in. Average. In. Sq. in. Tons. Tons. Tons. 24, round ... 8 ... 4’90 . .. 10’19 .. . 1*971 3 „ ... 8 ... 7’06 . .. 12’95 .. . 1’69 | 34 ,, 8 ... 9’62 . .. 15’00 .. 1’56 I ... 1’69 4 „ ... 8 ... 12’56 . .. 19'43 .. . 1’55 f 4| ,, 8 ... 15’90 . .. 26’71 .. . 1’68 5 „ ... 8 ... 19’63 . .. 32’91 .. . 1’67 J 6, quartered 8 .. 7’06 . 8’83 .. . 1’25) 7 „ ... 8 ... 9’62 . .. 12’42 .. . 1’29 J- ... 1’28 8 „ ... 8 ... 12’56 . .. 16’40 .. . 1’31) Table III.—Average of a Number of Tests of Crushing Strength of Baltic Timber ; Length, 4| ft. Description of prop. No. of pieces tested. Area .of prop. Total load on prop. Load per sq. in. Average. In. Sq. in. Tons. Tons. Tons. 3, round ... 4 ... 7’07 . .. 13’70 .. . 1’93) 34 4 ... 9’62 . .. 17’96 .. . 1-87 r ... 1’84 4 4 ... 12’56 . .. 22’29 .. . 1’77 C 44 4 ... 15’90 . .. 28’55 .. . 1’78) 6, quartered 4 ... 7’07 . .. 10’99 .. 1’58) 7 16 ... 9’62 . .. 13’19 .. . 1’37? ... 1’44 8 >> 8 ... 12’56 . .. 17’17 .. . 1’37) The figure 10-99 is an average of four pieces from one 6 in. prop. One prop (not included in the above table) with very twisted sun cracks—that is, running diagonally across the prop—gave the very low result of 6-81 tons. It was noticeable throughout the experi- ment that reasonable sun cracks, if more or less straight and parallel with the length of the prop, did not affect the strength of the prop, either whole or quartered, to any appreciable extent; but if the sun cracks were diagonal—say, to the extent of one- quarter circumference in 2 ft.—the quartered prop was greatly reduced in strength, and was quite unreliable. Table IV.—Average of a Number of Tests of Crushing Strength of Russian Timber: Length, 44 ft. Description of prop. No. of Area pieces of tested, prop. Total load on prop. Load per sq. in. Average. In. Sq. in. Tons. Tons. Tons. 3, round .. 4 ... 7’07 . .. 13’36 ... . 1’89) 34 ,, .. 4 ... 9’62 . .. 15’94 ... . 1’66 f 4 .. 4 ... 12’56 . .. 19’67 ... . 1’57 L 1/1 44 „ • .. 4 ... 15’90 . .. 27’34 ... 1’72) 6, quartered 12 ... 7’07 .. 9’25 .. 1’51) 7 .. 8 ... 9’62 . .. 12’41 ... 1’29 > ... 1’36 8 „ . .. 8 ... 12’56 . .. 16’41 ... 1’28) A test of an 8 in. quartered prop of red wood, not included in the above table, gave the high result of 18-56 tons. Table V. —Summary of all Tests (Tables I. , ir. in. and IV.) of Baltic and Russian Timber: Lengths, 18 IN. AND 44 ft. 1. 2. 3. 4. 5. 6. >7 Description Area Total Load Avge. Strength of load on per load per of various MX pXVp. tested. prop. prop. sq.in. sq.in. props.* In. Sq. in. Tons. Tons. Tons. Tons. 24, round ... 24 .. .. 4’90 ... 9’82 .. . 1’91) f 8’67 3 ... 32 . .. 7’07 ... 12’79 .. . 1’81 12’51 34 „ ... 32 . .. 9’62 ... 17’26 .. . 1’79 > 1’76 s 17’03 4 ... 32 .. .12’56 ... 21’08 .. . 1’68 22’23 44 „ ... 16 ., .15’90 ... 27 33 .. . 1’72 28’14 5 ... 8 .. 19’63 ... 32’91 .. . l’67_j L 34’74 6, quartered 40 . 7’07 ... 9 95 .. . 1’411 r 9-61 7 ... 48 .. .. 9’62 ... 13’33 .. . 1’38! ’ 1’36 ’ 13’16 8 ... 40 .. .12’56 ... 16’18 .. . 1’29 J 1 | ’ 17’08 * Calculated from average per square inch in previous column. From the foregoing figures it will be seen that there is a loss of 23 per cent, in the strength of cut props, as compared with round timber of equal sectional area. The figures suggest that quartered props may be used up to a length of 4| ft., provided that great care is taken to see that the prop is divided equally, and that there are no diagonal sun cracks. Table VI.—Average of a Number of Tests of Crushing Strength of Home-grown Timber from Scotland, Newly Felled and very Green ; Length, 18 in. Description of prop. No. of pieces tested. Area of prop. Total load on prop. Load per sq. in. Average. In. Sq. in. Tons. Tons. Tons. 24, round ... 8 ... . 4’90 . 7’02 ... 1’43) 3 8 ... 7’06 .. .. 10’72 ... 1’50 | 34 „ - 8 9’62 . .. 12’59 ... 1’31 1 ... 1’42 4 8 ... . 12’56 . .. 18’07 ... 1’43 44 8 ... 15’90 .. .. 20’84 ... 1’30 | 5 „ (dry) 8 ... 19’63 . .. 31’10 ... 1’58 J Table VII.—Average of a Number of Tests of Crushing Strength of Home-grown Timber from Scotland .- Timber of No. 6 test (Table VI.) seasoned in boiler- house for four months ; Length, 18 in. Description of prop. In. 24, round . 3 4 41 No. of Area pieces of tested, prop. Sq. in. 3 ... 4’90 4 ... 7’06 5 ... 12’56 3 ... 15’90 Load per Average, sq. in. Tons. Tons. 1’85) 2 05 f 2’00 1’87 f ” 2 00 2.23) Total load on prop. Tons. ... 9’08 . ... 14’53 . ... 23’50 . ... 35’60 . Partnerships Dissolved.—The London Gazette announces dissolution of the following partnerships: J. J. Stone (who continues the business) and Lieut.-Col. A. J. S. James, trading as Jarvis Stone and Company, coal factors, etc., 4, Southbourne-grove, Bournemouth; F. J. Ballard and J. B. Holden, trading as F. J. Ballard and Company, engi- neers, Dudley-road, Tividale; C. A. Hunton (who has retired), R. S. Hunton, and H. C. Hunton, carrying on business as C. A. Hunton and Sons, engineers, Gloster- House, Bishopsgate, E.C.