270 THE COLLIERY GUARDIAN. August 6, 1915. the degree of humidity, the lower the draught with a specified mean temperature. Should the air be cooled whilst its degree of humidity is increased, it becomes denser, and the draught is increased. With the air in the upcast shaft a somewhat similar set of conditions obtains, with reverse effects on the draught. A portion of the heat required to vaporise the water which is added to the air during its passage through the mine is abstracted from the water, rock walls, etc., thereby keeping their temperature lower than it otherwise would be, the balance of the heat being abstracted from the air. It should be particularly noted that in the neighbourhood of sprays and water blasts a much greater proportion of the heat will be obtained from the air than at points where there is no sprayed nor falling water. The temperature of the air being lowered, it becomes denser in the upcast shaft than otherwise it would be, and the draught is reduced in intensity. The mean cubic foot of air in the downcast contained 0-00083 lb. of water vapour; when raised to 90 degs. Fahr, temperature and 100 per cent, saturated, the volume will be increased to about 1-09 cu. ft., and it will then contain about 0'00232 lb. of water vapour. Therefore, to that volume of air in the upcast shaft representing 1 cu. ft. of saturated air in the downcast shaft there has been added 0'00149 lb. of water vapour, which has absorbed from rock, water, and air over 1'5 British thermal units of latent heat. As in the case of the downcast air, it can be assumed that one-sixth of this heat (or about 0-25 British thermal unit) has been derived from the air, and the air temperature has been reduced about 15 degs. Fahr, below what it would have been had all the heat required to exaporate the water been derived from sources other than the air. Had the air not parted with heat before reaching the upcast, it would have been at a temperature above 90 degs. Fahr., probably at 105 degs. Fahr., and, being less dense, the draught would have been correspondingly improved, so that, though the greater the degree of humidity in the upcast air, the higher the intensity of draught with a specified mean temperature, should the air be cooled whilst its degree of humidity is increased, it becomes denser and the draught is reduced. Thus a further law is established :—(5) The greatest intensity of draught produced by natural means is obtained when no heat is abstracted from the air itself except in the downcast shaft (i.e., when water is only sprayed into the air in the downcast shaft). The statement of this law should not be construed into an advocacy of the disuse of sprays and water blasts where these are necessary for the laying of dust or the absorption of deleterious gases. This necessary work must be performed in whatever manner is found advis- able, irrespective of whether natural draught is inter- fered with or unimpeded, and, so far, no method more suitable than water blasts and sprays has been devised. If, under the conditions prevailing, it becomes difficult to obtain the requisite draught by natural methods, arti- ficial means or mechanical appliances must be resorted to. It is, of course, common knowledge that water, when brought into sufficiently intimate contact with CO2, will absorb its own volume of that gas, irrespective of the pressure which the gas and the water are under. Therefore, under the most favourable conditions, the water passing through sprays and water blasts will become saturated with CO2. The author believes that a great deal of the corrosion of underground pumps, pipes, etc., is due to the presence of quantities of C02 in the water. There is one further aspect of the influence of the vapour in saturated air to which the author wishes to direct attention. Medical men, if they have not done so, might well investigate the results on human beings due to (a) the variation in the volume of air which must be inhaled under varying pressures and tempera- tures in order that the requisite weight of oxygen shall reach the lungs; (b) the modification of these volumes owing to water vapour saturating the air to a high degree of humidity; (c) the condensation in the lungs of water vapour from saturated air at a temperature considerably higher than that of the body. It would seem that when a person breathes saturated air at a temperature above blood heat there must be a condensation of water vapour in his lungs, and the resul- tant water (almost certainly carrying deleterious gases or matter, if the person is in a mine) must have a detri- mental effect on the lungs, and retard them in the efficient performance of their functions. It is common knowledge that on the surface, if the temperature is high and the air humid, men cannot perform the same amount of work that they can when the temperature is low and the air comparatively dry; it is also known that with a constant high temperature the lower the degree of humidity the greater the amount of work which a man can perform. This being so on the surface, it must be equally so underground, when the air is as fresh as on the surface, and more so when the air is contaminated with deleterious gases; the author thinks that this is not in any way attributable to “laziness” developed by dark places, and the impossibility of continuous super- vision, but should be ascribed to the inability of the lungs to handle the extra volume of air which is requisite to provide the necessary weight of oxygen, the lungs being to some extent waterlogged by condensed water vapour and by the moisture which would normally be absorbed by the non-saturated air in its circuit in the body, but which cannot be taken up by the saturated air. At sea level, with a shade temperature of 105 degs. Fahr, and air alternatively dry, 50 per cent, saturated, and 100 per cent, saturated, the relative volumes of air requisite to give the same weight of oxygen stuff, and the weight of water vapour carried by the air would be : Cubic feet of air:— Dry air. 50% saturated. 100% saturated. 1,000 .... 1,037- .... 1,080'S Lb. water vapour 1-77 lb....... 3'54 lb. Therefore, in order to absorb a given weight of oxygen, the rate of breathing air at 105 degs. Fahr, would be increased 4 per cent, with 50 per cent, saturated air, and 8 per cent, with 100 per cent, saturated air, as com- pared with the rate when breathing dry air. If the air had been at 70 degs. Fahr., the rate of breathing neces- sary would have been about 6 per cent, lower with dry air and 4 per cent, lower with 100 per cent, saturated air if compared with dry air at 105 degs. Fahr., or about 13 per cent., and 10 per cent, if compared with saturated air at 105 degs. Fahr. The 1,080-6 cu. ft. of saturated air at 105 degs. Fahr, on being inhaled, would shrink to about 1,052'8 cu. ft. of saturated air at blood heat (98-4 degs. Fahr.), and would then carry about 2'87 lb. of water vapour, the reduction in temperature causing about 0-67 lb. of vapour to be condensed in the lungs, and presumably retained there until a non-saturated atmosphere was available for respiration. Allowing the weight of oxygen per person previously deduced from Trautwine’s figures (0-0088 to 0'0178lb. per minute), the air inhaled per person per eight-hour shift would be from 330 to 680 cu. ft.; from this volume there would be from 0-207 to 0-42 lb. of water vapour condensed in the lungs. The author admits that this instances the most extreme case, and he simply uses it to indicate how serious a state of affairs could arise. If the air was only partially saturated when inhaled, there would.be a decreasing amount of water vapour con- densed as the humidity decreased, until, at about 80 per cent, saturation, there would be no condensation at all, but, at the same time, no moisture would be absorbed by the air during its passage through the lungs, etc. The author is not aware of any systematic record of the humidity of the air in mines having been kept; from a few tests he has made he is inclined to think that from the time the air reaches the bottom of the downcast until it reaches the foot of the upcast it is almost fully Effete saturated. He concedes that the number of tests he has made is an insufficient basis for any definite statement on the point. It is impossible for a layman efficiently to consider the medical aspect of the case, but the indication of what must happen when high temperature, highly saturated air is inhaled may lead medical experts to conclusions which will help to relieve underground workers of many disabilities when employed in hot humid atmospheres. The author therefore makes no apology when asking medical men to investigate the subject. The following are the author’s final conclusions :— (1) Air should be cooled as much as possible before it enters the downcast shaft; whilst it is being cooled it should be kept as dry as possible unless the heat used to evaporate the water is abstracted from the air, thus lowering its temperature and making it denser. (2) In order to attain the most intense ventilating current by natural means, the air in the workings and in the upcast shaft should be kept 100 per cent, saturated, but the heat used to evaporate the water must not be taken from the air. The spraying of water on to walls and heaps of rock tends to increase the draught intensity. Spraying water into the air itself reduces the draught intensity. (3) In the downcast shaft falling water aids ventila- tion by (a) the mechanical effect of drawing air downwards; (6) cooling the air and making it denser: it retards ventilation by saturating the air and making it less dense. The balance of effects is in favour of its increasing the ventilating current. (4) In the upcast shaft falling water causes reverse effects to those in the downcast shaft. The balance of effects causes a reduction in draught intensity. (5) Water having been once used for spraying pur- poses in situations where deleterious gases are absorbed, should not be used again for spraying, as some of the entrained gases will be released to the atmosphere when a portion of the water is evaporated. (6) CO2 absorbed by the spray water should be removed therefrom before the water goes to the pumps, to avoid corrosion in the pumps and piping. (7) If there are ill effects caused by inhaling hot saturated air, the air should be cooled before going to working places. This could be effected by the instal- lation of small electrically-driven refrigerating plants at necessary points in the mine, and passing the ventilating air through cooling chambers. A NEW TYPE OF BOGIE HOPPER WAGONS FOR THE BENGAL COAL TRAFFIC. The accompanying photograph illustrates one of 66 bogie hopper coal wagons of a new type which are now being delivered by the Birmingham Railway Carriage and Wagon Company Limited, of Smethwick, Birming- ham, for special service over the Bengal-Nagpur Railway system. These wagons, which are of all-steel con- struction, and are built for the 5 ft. 6 in. gauge, have the following leading dimensions :—Length of under- frame, over buffers, 44ft. Ilin.; length of under-frame, over headstocks, 40 ft. 9 in.; length of body, 35 ft.; width of under-frame, 9 ft.; centres of bogies, 29 ft. 3 in.; buffer height, unloaded, 3 ft. 7|in.; height of wagon from rail, 9 ft. 9 in.; centres of hoppers, 10 ft. 9 in.; hopper doors, 3 ft. 6 in. by 3 ft. 6 in.; centres of journals, 7 ft. 4 in.; wheel base, 6 ft.; diameter of wheels, 3 ft. lin.; journals, 10 in. by 5| in.; tare weight, 22 tons; and gross weight, 64 tons. The wagon under-frames are constructed of solebars built up of plates and angles running the whole length of the wagon, channels and pressed members running the width of the under-frames, all framed, kneed, and gusseted together. The body is built up of steel plates, 7 lb. per sq. ft., supported by tee and channel stanchions, pressed, flanged gusset plates taking the end thrust. The two bottom doors are each 3 ft. 6 in. square, working horizontally, and operated from either side through the medium of rack and pinion gearing in conjunction with hand wheels and Bramptons’ roller chains enclosed in a specially constructed case. This arrangement of rapid discharge has been found to work in a satisfactory manner. The bogies are of the built-up pattern with fin. sole-plates and channel. Cross bars and headstocks with laminated bearing springs are provided, being carried on the top of the axle box, and fitted with spring hangers attached to brackets riveted to the bogie sole- bars. The axle boxes are of cast steel, fitted with gun- metal bearing lined with white metal. The buffers are of the plunger type, having cast steel cases and plungers of mild steel, and fitted with both steel and volute and indiarubber springs. The wagons are provided with both side chains and screw couplings and standard draw- gear. The brake is of the combined vacuum and hand lever type, having 21 ft. cylinders (E class) with 1 ft. 2 in. diameter vacuum cambers and side lever hand brake actuating on all wheels of each bogie. The wagons were built to drawings approved of by Sir John Wolfe Barry, Lyster and Partners, of Westminster, the consulting engineers of the Bengal-Nagpur Railway Company, and under their direction and supervision. Immingham Coal Exports.—Returns for the week ending July 30 show that the coal exported from Immingham con- sisted of the following:—Foreign : To Dieppe, 1,777 tons: and Dunkirk, 844 tons. Coastwise : To Ramsgate, 220 tons; and London, 960 tons. Total. 2.621 tons foreign, and 1,180 tons coastwise, against 49.529 tons foreign, and 5,910 tons coastwise during the corresponding week last year.