March 23, 1917. THE COLLIERY GUARDIAN. 579 revolutions, and operating 300 kw. shunt dynamos; one compound tandem Collmann engine, running at 115 revolutions, and driving a 600 kw. shunt-wound dynamo; and a parallel compound Sulzer engine, running at 115 revolutions, and operating a 750 kw. shunt generator— the total output being 1,950 kw. The steam is super- heated to 280 degs., and admitted under a pressure of 140 to 1701b. per sq. in. The traphase plant consists, of a Brown - Boveti turbine, speed 3,000 revolutions, driving a 750 kw. alternator by the same makers, and two Zoelly turbines, speed 3,000 revolutions, with Leblanc condenser, and driving alternators (Society Alsacienne), with a joint capacity of 3,000 kw.—the total output being 3,750 kw. Two groups of 500 kw. transformers, running at 600 revolutions, enable the triphase current to be stepped down to direct current of 280 volts. The triphase plant is connected to the Campagnac power house, which com- prises a piston-valve Dujardin engine, driving a 240 volt, 3,150 kw. Westinghouse alternator, whilst two small vertical Boulte-Larboriere engines, running at 380 revolutions, drive 80 to 100 kw. generators (Soctetd Fig. 3.—Otto Coke Ovens. Alsacienne) for producing the 500 volt direct current used in the Campagnac group. The total capacity of the power stations is thus about 6,140 kw. The Lacaze station, which supplies about 10 million kilowatts per annum for the various purposes of the mines and works, is connected to the mains of the local electric power company, which supplies current at 38,000 volts, this being stepped down to 3,300 volts at Lacaze. Coke Oven Plant (figs. 3 and 4). Three batteries of Otto-Hoffman by-product coke ovens (99 ovens in all) are in operation, and a fourth battery, of 37 ovens, is in course of construction. The ovens are of the following dimensions: Length, 10-30 m.; width, 60 cm.; height, 17 m., and each holds a working charge of seven tons. The coking period is approximately 40 hours, and the yield of dry coke about 69'2 per cent. The small coal is compressed, and charged by machinery, and the coke is ejected by two electric pushers of 40 horse-power; the smalls coming directly from the wash- ing plant on a belt conveyor are delivered into draining hoppers, and are taken thence by a second belt and mixed with 10 per cent, of anthracite on their way to the Carr breaker, the crushed mixture being stored in large hoppers. The gases from all the ovens are led to the by-product plant, where they are stripped of their tar, ammonia, and benzol. The ammonia is converted into sulphate on the premises, and the benzol is rectified for sale, whilst the tars are sent to Campagnac for treatment. Each ton of dry coal charged into the ovens furnishes 30 kilogs. of tar, 10 kilogs. of sulphate of ammonia, and 6 kilogs. of benzol. There is also a coking and by-product plant at Cam- pagnac, with a battery of 30 Seibel 5-ton ovens, working a charge in about 48 hours. The tar, ammonia, and benzol' are recovered, the last-named being sent to Decazeville for rectification. The whole of the tars are dehydrated and distilled, the heavy oils and creosote being sold, whilst the pitch is made up into ovoid briquettes with the small coal. The War and Iron Ore Contracts.—The House of Lo-ds on Monday dismissed the appeal of the Ebbw Vale Steel, Iron and Coal Company, who sought a declaration that the respondents, Macleod and Company, were noi entitled to suspend the operation of two contracts for the sale by (the respondents to the appellants of iron ore from Spanish mines. The respondents contended that the war has affected the mines from which the ore had to be obtained, and also the ships by which the ore was to be conveyed. Mr. Justice Bailhache had held that the respondents were entitled to succeed, on the ground that the war had affected the mines. This view was upheld by the Court of Appeal, and has been confirmed by the House of Lords. REFRACTORY MATERIALS. A meeting of the Refractory Materials section of the Ceramic Society was held at Leeds University on the 13th inst., Mr. William Oates presiding. Zirconia as a Refractory Material. In a paper by Mr. J. A. Audley, B.Sc., on “ The Use of Zirconia as a Refractory Material,” it was stated that the melting point of native zirconia is nearly 2,000 degs. Cent., and much higher for the purified material. Even crude zirconia resists both acid and basic slags, as well as fused cyanides and alkalies. Its conductivity for heat and coefficient of expansion are both very low, and it can be plunged red-hot into water without suffering fracture. In Germany, zirconia bricks have been used to line the hearth of a Siemens-Martin (open-hearth) steel fur- nace with satisfactory results. Over 50 per cent, was saved in maintenance costs compared with the refrac- tory lining generally used, without taking into account the increased production and higher efficiency obtained by the use of zir- con i a. Zirconium steel has been used in Germany for armour plates, etc., and it is stated that 1 in. armour plate of such steel is equal to 3 in. armour plate of the best German steel. Before the war, zir- conia was sold in Ger- many for £31 per metric ton (2,2041b.) of the crude material, and .£35 to £50 per metric ton of powdered purified material. E. Podszus reports that fused zirconia is well suited for making refractory ware, burned at 2 ,300 t o 2,400 degs. Cent. The furnace used is chiefly made of fused zirconia and the fuel being coal gas, petroleum,’ or acetylene, with air blast first, and finally oxygen blast. Ruff and Lauschke recently found the mean melting temper- ature of pure zin coni a to be 2,563degs. ± 10 degs., and that crucibles of pure zirconia did not fall to pieces when burned at 2,000 degs., and only slowly at 2,200 degs., but collapsed quickly when burned at 2,400 degs. Addition of 3 per cent, of alumina to the zirconia greatly re- duced this tendency, and an addition of 6 per cent, completely prevented falling to pieces, even when burned at 2,400 degs. The general 'conclu- sion was that compact useful r e f r a c to r y articles were best ob- tained by adding to zirconia, for burning at or below 2,000 degs., about 1 per cent, of alumina; for burning at 2,200degs., about 1 per cent, of thoria; and for burn- ing at 2,400 degs., about 1 to 3 per cent, of yttria. Larger ad- ditions are useless, and increase the poro- sity. The Spalling of Mag- nesite Bricks. Dr. J. W. Mellor, in reading a paper on this subject, said that magnesia from cal- cined magnesite occurs in two different Fig. 4.—Coke Ovens and By-product Plant. forms, one having a specific gravity of 3'2, the other 3'7; the low specific gravity form also displays greater chemical activity. The conversion from the lower specific gravity form to the higher specific gravity form by calcination takes time; the higher the tempera- ture of calcination, the faster the transformation. Different types of magnesite have their own specific rates of conversion. There are two important primary causes for the spall- ing of magnesite bricks : (1) The shrinkage caused by the change of calcined magnesite from a form with a low to a form with a high specific gravity. Ordinary magnesite bricks may contract 7 or more per cent, (by volume) from this cause. The obvious cure is to shrink the magnesite as completely as possible before the bricks are put on the market. (2) The shrinkage caused by the closing of the pores, a phenomenon which normally occurs during the firing of the granular materials employed in the ceramic .industries. Some magnesite bricks on the market have a porosity between 19 and 20 per cent., and the pores have been found to close up until the porosity was 11 per cent., while the bricks were in use in an electric furnace. The resultant of the two effects, shrinkage of the magnesite, and the closing of the pores, produce a contraction of nearly 16 per cent, by volume, or 5’8 per cent, linear. The strains set up by a sudden chilling of the hot furnace may aggravate spalling primarily produced when bricks are made with too high a porosity from imper- fectly shrunk magnesia. If no serious factor has been overlooked, it ought to be possible to determine by pre- liminary tests whether a magnesite brick is likely to spall seriously, and the manufacturer ought to be able to obtain definite objectives in order to reduce spalling to a minimum. For the purposes of a specification for magnesite bricks, a contraction test analogous with that of the gas engineers’ specification could be devised, or permissible limits for the proportion of unconverted magnesia, and also for porosity, could be adopted. The Dressier Kiln. Mr. 0. Dressler next read a paper on “ The Dressier Kiln,” with special reference to its application for annealing steel under what is claimed to be complete and easy control. Thermometry in Clay Works Practice. In the evening, Prof. J. W. Cobb lectured on “ Tem- perature Measurements in Clay Works Practice.” He described the various instruments used, and where neces- sary explained the principles on which their employment depended, with the precautions to be observed. Mention was made of several forms of mercury thermometer, including one with compressed nitrogen above the mer- cury (available for temperatures between 250 and 450 degs.), thermo-couples, recorders for indicating the pro- gress of the heating, the Fery radiation pyrometer, and an optical pyrometer in which varying resistance changes the luminosity of a lamp filament. Since a lower temperature acting for a longer time can produce the same effect as a higher temperature acting for a shorter time, the mere determination of tempera- ture is not sufficient to show the temperature-time-atmo- sphere effect, and other methods of control are required. In this connection were mentioned Watkins’ recorders, Seger cones, Holdoroft bars, the Wedgwood pyrometer, and Buller’s rings. While testifying to the value of Seger cones, Prof. Cobb said they would be much better if made larger and of rather different shape, and he hoped that now they were being made in England their disadvantages would not be perpetuated. Paris Coal Prices.—In consequence of the modifications which have taken place in the relative supply of English and French coals since the Pari-s prices were originally fixed, the following new list, showing a reduction of 10 fr. per ton, has been issued as from the 15th inst. :—Dealers having storage : Screened flaming coals, 130 fr.; unscreened (60 to 70 per cent.), 120 fr.; non-flaming coals, screened, 140 fr.; unscreened, 115 fr.; ovoids, 120 fr. Small retailers having no storage : Screened flaming coals, 135 fr.; unscreened (60 to 70 per cent.), 120fr.; non-flaming coals, unscreened, 120 fr.; ovoids, 125'fr. In all cases the prices include octroi dues. For suburban sales, the various differences in the octroi dues are to be taken into consideration. Scale “ Locators.”—For localising the deposits of scale in specially-designed and constructed sets of baffling and dis- tributing plates, ‘‘locators” have been introduced by the Lawrence Patent Water Softener and Sterilizer Company, and have been used successfully by them in their several types of water heating, softening, and sterilising plants and apparatus. These plates are designed and constructed in different forms and sizes to suit the conditions and require- ments, and have proved effectual in collecting scale which otherwise would adhere to the interior surfaces of boilers and tanks, and be difficult and expensive to remove. The plates can be taken out for cleaning, -which is easily effected by tapping the hard scale with a light hammer; and if a spare set is kept, the boiler or tank need not be put Out of use.