546 THE COLLIERY GUARDIAN. September 13, 1918. considered, namely, width and value. Obviously a sample assaying 100 dwt. over a width of 10 in. averaged with another assaying 10 dwt. over 6 in. does not give us 8 in. of reef averaging 55 dwt. The method used for averaging the above samples would be as follows: The assay value of any section is multiplied by the number of inches over which the sample has been taken. This gives a figure which is termed “ assay inches ” or “ inch dwts.” To obtain the average width of reef in a-heading the inches of each section are added together, and this total is divided by the number of sections taken. The average value of a block is obtained by adding together the “ inch dwts.” of all sections taken, and this is divided by the total inches. In using this method of obtaining the average width and value, it is necessary that the sections should have been taken Fig. 4. at equal distances apart. If this has not been done, the samples must be weighed on their length and expressed as “ feet inch dwts.” A simple example of this method of valuing where samples have been taken at equal intervals is as follows: — Sections. Inches. Dwts. Inch dwts. 1 10 100 1,000 1 6 10 60 «... — ——- ■■ ■ ■ 8 2 16 — 1,060 The total inches divided by the number of sections gives the average reef width, namely, 8 in., and the total ‘ ‘ inch dwts ’ ’ divided by the total inches gives the average reef value, namely, 66-25 dwt. It has already been pointed out that in valuing blocks the values must always be weighed on the lengths over which they are taken. INSTITUTION OF MINING ENGINEERS. MEETING AT NOTTINGHAM. The 29th annual general meeting of the Institution of Mining Engineers was held to-day at the University College, Nottingham. A report of the proceedings will appear in our next issue.. The newly-elected president, Mr. George Blake Walker, M.Eng., M.Inst.C.E., then gave his presidential address. The President thanked the members for the great honour of his election as president of the institution. We had now, he said, entered upon the fifth year of this terrible European war. Every section of the com- munity had had to bear its share of the loss, incon- venience, and cost which that war had involved, and the mining industry had had its full share of the heavy toll of life and limb as the result of the conflict. It seemed to be admitted .by our generals that the men who had gone forth as representatives of the mining community had distinguished themselves by their valour in the field beyond most other classes of citi- zens, and by their resource and ingenuity in connec- tion with the different problems for which they had had to qualify themselves in a very short space of time. In particular, he referred to the tunnelling companies of the Royal Engineers, whose services in connection with the earlier stages of the war were described by Lord French as being unsurpassed by any other branch of the service. More would be heard when the troops returned of the considerable engineer- ing works which the miners had helped to carry out. It must never be forgotten that ours was essentially a citizen army; our men had had no previous training for war, and they had had to adapt themselves to fight with a nation who for generations had been carefully preparing for this struggle, and had been equipped with the most diabolical engines of destruction ever devised. We had, therefore, great cause for thankful- ness and pride for the part which the mining com- munity had borne in this war, and that hitherto the decision had not gone against us. But it was not merely in the field itself that the importance of the coal mining industry had been emphasised. We had had to supply not only our own requirements, and provide fuel for the immensely increased output of munitions and material necessary for the war for our own armies, but we had had to supply the Allied nations, especially France and Italy, with coal. The French coal fields had been overrun by the Germans, and their plants as far as possible destroyed, and those which had not actually been destroyed had been prevented from producing coal; hence the burden of supplying our Allies with the materials for continuing their munition industries, their transport, and their domestic consumption had fallen almost entirely on this country, and had pro- duced a very serious shortage that would make coal scarcer than ever. This shortage had emphasised the immense importance of our coal industry to ourselves and the world at large. It behoved us, therefore, to the Dolcoath Mine, Cornwall, it was about 1 deg. Fahr, for every 60 ft., whereas in the deep mines near Bir- mingham the rate of increase was only about 1 deg. in about 110 ft., and in the Transvaal the increase was a great deal less, namely, about 1 deg. in 220 ft. But it was not only the rock temperature which had to be contended with. In our deep coal mines a very considerable increase of temperature was due to the oxidation from the strata which were being worked, and unless there was a very powerful ventilation the heat given off by oxidation mightbe greater than that due to the temperature of the rock itself. There was also the less important source of heat from compres- sion, which warmed the air about 5^ degs. Fahr, for every 1,000 ft. of depth. Dr. Haldane had written as follows : The living human body is a marvellously efficient ther- mostat ; but there are limits to what it can do without artificial-aid. Some years ago, when I was investigating the ventilation of Cornish mines, I determined on myself its limits in the upper direction. . . . My ex- periments showed that in still air and during bodily rest the body temperature began to rise as soon as the wet-bulb temperature exceeded 88 degs. Fahr. It did not matter in itself what the actual temperature of the air was, or what its dew-point or absolute percentage of moisture, or relative humidity were. Air at 150 degs. produced just the same effect on body temperature as air at 88 degs. if in each case the wet-bulb temperature was 88 degs. . . . It is only when one is at rest that one can keep the body temperature normal in still air at 88 degs. During muscular exertion a considerably lower wet-bulb temperature is needed. Of course cloth- ing is also of much importance. At wet-bulb tempera- tures over 80 degs. a man cannot do much continuous work in still air, even with nearly all clothing removed. . . . When the body temperature begins to rise owing to a high wet-bulb temperature, it does not stop rising, so far as I am aware, till death occurs, or till removal to cooler surroundings.* It might be said generally that the wet-bulb tem- perature of the air in the working-places of a mine must not exceed 82 degs. Fahr, in order to support the conditions of human life, and we were rapidly approaching that temperature in many of our mines. There were cases in the neighbourhood of Doncaster and in Lancashire where these temperatures actually prevailed. Sir John Cadman, in a paper he read before the North Staffordshire Institute of Mining and Mechanical Engineers,* cited a number of instances in which this temperature was reached. He cited a case (No. 25, page 517) where the dry-bulb tempera- ture was 111 degs. and the wet-bulb 82 degs. Fahr. He made the following remark: Large current of air passing here ; men were working naked, pushing wagons about. The writer did not feel any great inconvenience, perspired freely, and moisture evaporated from the body very quickly ; quite comfort- able at rest; eyes felt a little burning sensation. Rails and wagons felt hot to the touch. Obviously, despite a good ventilation, not much useful work could be done under such conditions. SI IZ 4«4 14 ? « / 21 TT1 111 11 | , i f] | 11'| HTTi UH i 25 0- tS.€ BLOCK 2. Ip 3t 18 to 26 <4 *0 / * in (5 5 *25-4 in N rJ IS 4 :si 121 BLOGK I ~zzT 33 7 a? IZO as 5 14 It 2 O ’ I i 385 22 O /5 3" — Fig. 5.—Assay Plan. 14 V 8-5 V-c 2. « IS-4 411 TO IQ, ? IO J !7 a if 41 18 14 I i# Q at ___ . 8Level West. For the purpose of illustrating this, fig. 5 is a plan of two blocks from which no ore has been stoped. All the sides of Block 1 have been exposed by drives and winzes, there being two winzes and two drives, namely the 7th and 8th levels. Block 2 is bounded by one winze and the two drives, the fourth side being defined by a dyke. All the values shown on this assay plan are calculated over the “reef channel,” which term has already been explained at the beginning of this paper. It will be obvious that values expressed on the reef width only may be very misleading, since the layers of reef may be separated by large waste partings, and in consequence the only reliable width which can be used is the “ reef channel.” For example, two sections of reef, each 10 in. wide, assaying 20 dwt. and separated by 10 ft. of waste, are unpayable, whereas if only separated by 2 ft. of waste the reef can be w’orked to excellent advantage, and would prove a highly payable proposition. Before valuing a block of ground, each section is examined individually, and by this means the surveyor is able to form an opinion as to which sections of the reef will be worked, and what the reef channel will be, and by expressing values over reef channel it will be seen at once whether the block is payable or not. (To be continued,) look with the greatest care and anxiety on what the outlook for the future really was. The Government had appointed a Committee on Scientific and Indus- trial Research, and no doubt the Institution of Mining Engineers would be asked to co-operate in the enquiries into several important matters, amongst the most important being the question of the conditions of mining at great depths. Temperature of Deep Workings. Everyone was aware that the period through which we had passed during the last half century was the most favourable for the production of abundant and cheap coal. We were working seams which lay within a moderate distance from the surface, and where the conditions of temperature were such that labour could be employed without imposing conditions prejudicial to human effort. But that period was rapidly drawing to a close, and we were now confronted with the pro- blem of coal that would have to be worked at depths where the conditions would make the results of human labour far less effective. Dr. J. S. Haldane had devoted special attention to the conditions under which it was possible for human beings to do laborious work where high temperatures prevailed. As we went deeper into the crust of the earth, it was well known that a progressive increase in rock temperature occurred with increasing depths. There seemed to be a good deal of variation in the rate of increase. At According to Dr. Haldane, the body temperature of the human being must not rise above 102 degs. Fahr, or fatal results would probably occur. Even with the wet-bulb temperature at 78 degs. Fahr., the body tem- perature could hardly be prevented from rising during7 moderate work in still air. In a good air-current, on the other hand, continuous moderate work was pos- sible with the wet-bulb at 85 degs. Fahr. The relief afforded by evaporation through perspiration was the all-important safeguard; but there were, of course, practical limits, and although a higher temperature might be sustained for a short time, 100 degs. Fahr, dry-bulb might be taken as the limit for practical pur- poses of the temperature at which men could work, and at such temperature efficiency would be greatly reduced. From figures which had been furnished, he found that at a depth of 1,950 ft. the dry-bulb temperature in the working-places of one of the newest and best equipped collieries in South Yorkshire, with an ample ventilating current, was generally 74 degs. Fahr. At a depth of 2,220 ft., at another colliery near Doncaster, the temperature in the working-places was generally 80 degs. Fahr. In a third case in the same neighbour- hood, at a depth of 2,730 ft., the temperature was with * Trans. South-Eastern Union of Scientific Societies, 1917, pages 71-73. * Trans. Inst. M.E., 1912-1913, vol. xlv., page 509.