260 ____________________________________________________________________________________________________________ THE COLLIERY GUARDIAN. August 11, 1916. panies have portable sub-stations, which can be rushed to any part of the field for use in emergencies. (5) Absence of danger from presence of high-pressure boilers. (6) Power expense shown in one bill and economies in the use of power directly show in same. One large operator is now using only 30 per cent, of the current for operating his fans that was necessary three years ago, and the cost of mining coal has been decreased 20 per cent. This manager states that it was the saving effected in the use of power that led him to make other economies. (7) The power is delivered at most advantageous point, from a power user’s standpoint, while with individual plants, water supply, coal supply and other things deter- mine the location. (8) Experience of others who have tried it overwhelm- ingly in its favour. (9) Improvement in the design of line material and automatic equipment is enabling the central station to give a practically uninterrupted supply of current. (10) Lack of labour supply. (11) Last, but not least, is the operating cost. This is put last because the cost of power is a relatively small part of the cost of mining coal, and the points above mentioned, in many cases, far outweigh any slight increase or decrease in the cost of power. With new mines, in practically all cases, the cost of operation, including interest on investment and depre- ciation on equipment, is less with purchased power, whilst in old mines, each mine presents a case by itself, and in some mines a large saving would be shown by a change, while in others a loss would result. In most cases where a mine has bone coal that can be used in the power plant, a loss would result, although even here, in some cases, the extra labour, extra main- tenance of boilers, etc., result in a cost which can be met by central station service. From the central station viewpoint many coal owners cannot understand how a central station can supply them at a profit, and are afraid the central station will get them all connected up, and then raise the rates, as the mine owners realise that the central station owners are in the business for the same reason as they are, viz., to make money. Some of the reasons why central stations can afford to furnish power at as low or lower than the mine owners can produce it for are as follow :— (1) The diversity of the customers’ peaks. The cen- tral station does not have to instal twice as much equip- ment to supply two mines as one. (2) The central stations, installing, as they do, larger units than the mine owners, do so at a lower cost per unit. (3) The load of the central station is constantly grow'- ing, so that new units are installed frequently, and advantage taken of any better and more efficient methods of generating power. It takes no more labour to operate a 5,000 kw. unit than a 500, so that the central station can employ the highest grade of labour at a lower unit cost. This results in decreased cost of power. (4) The many large companies that are now availing themselves of central station energy, in some cases at slightly higher cost. _____________________ NEW AUTOMATIC STOKER * The illustration shows stoking apparatus which is designed with a view to the more efficient charging of furnaces. These machines fire the coal in small charges of about fib. at each charge. If connected to a steam engine equipped with an automatic regulating valve, it is said that an even steam line can be maintained. If The new stoker. ”“x. && regulation is not desired, then the stoker is connected with any line shaft, or may be operated with a small motor. The installation of this apparatus does not require the removal of the furnace doors, or any altera- tions in the boiler front or furnace. Owing to its small size and compactness, the machine does not interfere with the operation of the furnace by hand. * Black Diamond. ________________________________ The coal tippers of Cardiff and Newport demand a 25 per cent, increase of wages. A commission agent at Newcastle (N.S.W.) desires to secure the representation in New South Wales of United Kingdom manufacturers of goods saleable to collieries. Manu- facturers may obtain the name and address on application .to the Commercial Intelligence Branch of the Board of Trade, 73, Basinghall-street, London, E.C. In making application the reference number (240) should be quoted. CURRENT SCIENCE Synthesis of Ammonia. Nitrogen in its molecular state and under ordinary conditions is too inert to enter into combination. Atmospheric nitrogen has to be raised to high tempera- tures or exposed to high pressures of powerful electric discharges before it will combine with most other elements, whilst resulting products are liable to decom- pose again rapidly unless removed from the zone of reaction. From a communication which Dr. Zenghelis recently presented to the Academie des Sciences, it appears, howeve?, that ammonia can be synthesised from its elements, in the atomic, nascent state, and in the presence of catalysts. In one series of experiments, a mixture of the gases—three parts by volume of hydro- gen and one part of nitrogen—was passed through water (at 90 degs. Cent.), in which a finely divided metallic catalyst was suspended. The yield of ammonia was very poor, nor did electrolytic and chemically-evolved hydrogen give better results. In other experiments the nitrogen wras atomic, but not the hydrogen, the former being generated from sodium nitrite and ammonium chloride. But here again the yields were very low. In a third series both the elements were in the nascent state, and decidedly promising results were obtained. The temperature ranged from 70 to 99 degs. Cent. Out of a theoretical yield of 5,000 cu. cm. of ammonia solu- tion, spongy palladium furnished 321 cu.cm., colloidal platinum 1,755 cu.cm., and colloidal palladium 1,025 and even 2,060 cu. cm., i.e., a yield of 40 per cent. Extracting Tar Fog from Hot Gas. In a paper read before the Society of Chemical Industry at Edinburgh, Mr. G. T. Purves stated that the ordinary devices used for fog extraction' being ineffec- tive, special methods have been applied, wdiich give a much more intense scrubbing action. On the Simon- Carves direct recovery plant the heavier fog is separated in a “ Cyclone ” extractor into the inlet of which a jet of ammoniacal liquor is forced. This unit acts in the same manner as do bends on the mains,. The principal extractor, however, which removes the lighter fog is a “ Dynamic ” separator, the vanes of which revolve at high speed. The peripheral speed is said to be over 200 ft. per second. The author himself had passed crude gas at 80 degs. Cent, through a five fan turbo-exhauster running at up to 2,000 revs, per minute, and although the extraction was not complete the bulk of the fog present was certainly removed, and this exhauster was not specially designed on the lines of a dynamic extractor. The result of this test indicates that with such an exhauster working on cooled gas special tar extractors might not be necessary. The energy required in a dynamic extractor is said to be 1 horse-power per 12,000 cu. ft. of gas per hour—presumably crude gas passing through the separator. When carbonising wet dross the volume of crude gas produced measured at the dew point will not likely be less than 20,000 cu. ft. per ton. So that on a 360-ton plant the energy required per day will be about 600 horse-power. The method of extraction patented by the Otto Hilgenstock Company was to scrub the gas with a spray of tar. A cluster of sprays were used in Germany, and were so arranged that any particular number of them could be used at once. This practice was not exactly followed by the Otto Com- pany in this country. The plant they erected at Auchen- geich has four sprays, and provision is left for adding two others. These sprays can be wTorked singly or two sets of two in series. They are served by a motor driven centrifugal pump, the capacity of which is 120 cu. m. of tar per hour at high pressure, and they are designed for treating the gas from 360 tons of coal per day. Before handing over the plant the Otto Company gave up the use of tar, and used instead a mixture of tar and liquor. They also used only one spray. The author prefers to use liquor as free as possible from tar, and a much smaller volume than that given above. The energy required at present per day is 360 horse-power. These figures show, in the designer’s view7, at least, the magni- tude of the difficulty of completely reproving the tar fog from hot gas. In order to see why hot tar extraction is so difficult one must consider the altered conditions of working. Direct ammonia recovery from hot gas has so far been applied only at coke oven plants (in this country at least). In these plants washed dross is used, and the coal when charged into the ovens usually contains from 9 to 13 per cent, of added water. This water is, of course, present in the gas as vapour at the fog extraction temperature, thus greatly increasing the volume. One might anticipate, as so much water accompanies the coal, and so cools the oven walls, that the outstanding effect of increasing the proportion of water would be the production of thinner tar possibly more difficult to extract. This is not the author’s experience. The most notable effect is the increased amount of pitchy matter which is deposited in the collecting main—not neces- sarily an increase of pitch made per ton of coal. The increased dilution of the gas by steam will have little effect on the volatility of the pitch product. This will readily settle out, and so the fog formed later on should be lighter. At the higher dew point an increased amount of the lighter tar will be retained in the gas as vapour, so counteracting the effect on the fog of the reduced pitch content. It is therefore not probable that the presence of so much water in the coal will make the fog extraction more difficult by the production of a lighter tar fog in itself. It might be, however, that under these conditions the fog particles are smaller, but it is very difficult to get experimental evidence in regard to this. We do not know how the composition of the individual fog particles is related to that of the bulk tar collected, but the rapidity of the cooling, and the time the fog particles exist as such in the gas, will have a material influence on their composition. AND TECHNOLOGY. Following on the treatment of the gas as regards rate of coking, the author made experiments, with a view to saving energy, on the spray extractor itself, varying the dimensions of same, the nature of the liquid used, and the pressure and volume of separation of the fog from the hot gas. The tars produced in the modern vertical retort differ greatly from those produced in horizontals and coke ovens, and mark a step towards those produced in so-called low-temperature carbonisation. Samples of the five tars—viz., I., heavy tar from direct recovery plant (coke ovens); II., tar from horizontal retorts; III., tar from Wilson continuous intermittent vertical retorts; IV., tar from Glover-West continuous vertical retorts; and V., tar from Woodall-Ducklam continuous vertical retorts—distilled under exactly similar conditions, gave the following results :— . I. Per c. II. Per c. III. Per c. IV. Per c. V. Per c. First runnings up to 110 degs. Cent. Oil trace .. . 2’6 ... 1’3 ... 2’6 . .. 3'5 Water 7’0 .. . 2’2 ... 1’7 ... 3’4 . .. 7’1 Light oil up to 210 degs. Cent. ... 1’5 .. 5’2 ... 4’5 ... 8'7 . 6’7 Carbolic oil up to 240 degs. Cent. ... 4’0 .. . 13'0 ... 109 ... 12’9 . 7’7 Creosote oil up to 27o degs. Cent. ... 8’4 .. 9’1 ... 12’1 ... 8’6 .. 8’6 Anthracene oil up to 350 degs. Cent. Water . 0’5 ... 0’5 ... 0’1 .. 0’6 Oil 19’6 . 20'6 ... 27’0 ... 20’4 . .. 27'1 Pitch 58’6 .. . 46'0 ... 40’6 ... 41’5 .. . 37'2 Loss 0’9 .. 0’8 ... 1’4 ... 1’8 .. 1’5 100’0 ... 100’0 ... 100 0 ... 100’0 ... 100’0 I. and II. contained both naphthalene and anthracene. III., IV., and V. showed no precipitate of naphthalene on cooling the oils. IV. and V. appeared to contain only a trace of anthracene, but the fractional when cold was semi-solid with paraffin. No. III. had not so much paraffin, but had a distinct amount of anthracene. These tars so widely dissimilar are mixed at the tar distillery and submitted to a uniform treatment. It may not be practical for tar distillers to deal with the different types of tar separately, but there does seem good reason for giving them selective treatment, and if fractional collection was adopted at the carbonising works each tar could receive the fractional separation most suited to its composition. Both anthracene and solid paraffins are valuable products, and well worth recovering, but when the tans are mixed the one substance fouls the other. Vertical retort tar, particularly when mixed with other heavier tars, might be expected to suffer more from decomposition during distillation, since it has not been cracked