February 22, 1918. THE COLLIERY GUARDIAN. 379 the oil switches are mounted on a pipe framework 6 ft. back of the panels, and connected to switch handles by means of levers and bell cranks. A 15-ton Morris Brothers double-beam hand-operated travelling crane, with a chain hoist, has been installed in the turbine room. Cooling the Generators. An interesting feature is the unusual arrangement of the air ducts for carrying cold air to cool the generators. At the company’s Rossiter power plant trouble was experienced with the generators, owing to the formation of ice on the outside by the condensation of the moisture in the air of the room, the generator being made too cool by the ice-cold outside air causing the condensed moisture to freeze. In other words, the generator acted as a suction fan, and sucked in more air than it could heat. In order to do away with this trouble, doors have been arranged at each side of the intake air duct, so that the amount of air passing to the generator can be regulated by opening or closing, thus maintaining an even temperature. Condensing Plant. The condensing equipment consists of two Alberger surface condensers, together with two 10 in. two- impeller turbo volute pumps direct connected to and driven by Alberger-Curtiss non-condensing steam tur- bines with two 2 in. Alberger standard volute condensate pumps mounted on the end of the pump shafts. There are also two 8 by 16 12 in. Alberger horizontal dry vacuum pumps. A vacuum of 27J to 28 in. is obtained with these pumps. PIT TIMBER DISPUTE. [From our Legal Correspondent.] It is not surprising that the House of Lords, following the Court of Appeal in Scotland, has thrown out the claim of the Oak bank Oil Company to recover £1,800 damages from Love and Stewart Limited, for cancella- tion of a contract for pit props. The contract was made very shortly before the war, to supply props to the Oil Company for a year, beginning in June 1914, and Love and Stewart cancelled it when war broke out. The papers were A. —Conditions issued by the Oakbank Company and signed by Love and Stewart. They contained nothing allowing c mediation. They also bore “ The company’s specifications, conditions and form of tender must be strictly adhered to and not altered in any way whatever, Parties not satisfied with the same should simply, there- fore, decline to tender.” B. —Love and Stewart’s letter containing their offer and enclosing the company’s conditions signed. At the top of the letter paper there was the following note in red ink:— “ All offers- over a period are subject to stoppages through strikes, lock-outs, etc., and the right to cancel is reserved in the event of any of the countries from which our supplies are drawn becoming engaged in war.” C. —The company’s letter accepting Messrs. Love and Stewart’s offer. The Oakbank Company put forward three posi- tions, all of which were treated as untenable. They said their conditions were unalterable. The conditions expressly so bore. By signing them Love and Stewart accepted that position and admitted the unalterable quality. Therefore no attempt to alter could have any effect. Consequently the conditions bad not been altered. Then they said they had not noticed the red ink note, and therefore they ought not to be prejudiced by it. The answer is that they ought to have noticed it. It was not hidden away in a corner. It was put in the forefront, at the top, in red ink, and in fair sized print Finally, they said it cannot be part of the contract unless it is part of the letter; and it can’t be that, for a letter begins with only “Dear Sir.” This may have been seriously intended, but if so it was not listened to in like manner. Altogether this may be regarded as an extraordinary action, justly ended, though—no doubt according to the rules of the game—Messrs. Love and Stewart are left to pay a considerable amount of legal costs which they cannot recover from the other side. Stone Dusting. — We are informed that a stone dust grinding mill is to be shortly installed by the Madeley Coal, Coke and Brick Company Limited, of Leycett, near Stoke-on-Trent. The machine selected is the “ Ideal ” mill manufactured by Messrs. Richard Scholefield, of Burley Vale Works, Leeds, and will be capable of pro- ducing approximately 10 cwt. of finished dust per hour, of which about 65 per cent, is fine enough to pass a test screen of 100 by 100 mesh. This will be the second mill of this capacity supplied by Messrs. Scholefield in the Stoke-on-Trent district, one having been recently delivered to the Sneyd Collieries Limited, of Cobridge, North Staf- fordshire, to replace an older system of grinding by means of an ordinary mortar mill. The “ Ideal ” mill was fully described in an illustrated article which appeared in our columns some time ago (January 12, 1917, p. 72), and is now in daily operation at some of the largest collieries in the country. Electrical Power in Yorkshire.—At the annual meeting of the Yorkshire Electric Power Company on Tuesday, the chairman (Mr. A. G. Lupton) stated that extensions of generating plant were contemplated. The company had laid down 358 miles of mains, passing through 91 separate districts, with 120 sub-stations or distributing stations. The company hoped for a further development of the co-operation of colliery owners. The company’s area of supply included the great Yorkshire coal field. Practically all the mines were outside the large towns, and the com- pany’s system provided the obvious means of conveying power generated in the coal fields to the various industrial areas. There could be no doubt that the national waste inseparable from small separate installations must be obviated.. One solution of the problem would be in the co-operation of large municipalities and the company, and that ultimately the supplies should be taken from a few large installations, which should be worked on a scientific basis for coal economy and the reclamation of by-products. THE MANUFACTURE OF SILICA BRICKS.* By H. Le Chatelier and B. Bogitch. A highly important factor influencing the quality of silica bricks is the physical and chemical constitution of the mixture submitted to the baking process. A general rule for the composition of silica bricks is to use quartz containing not more than 3 per cent, of basic oxides (iron, alumina, and alkalies), with an addition of 2 per cent, of slaked lime, in order to obtain finally a brick with not more than 5 per cent, of impurities. Beyond this proportion, the brick would become too fusible to be employed in a steel furnace, where it had to withstand a temperature of 1,700 degs. To produce a good brick it is necessary to study (1) the granulometric composition of the mixture, (2) the chemical condition of the silica, and (3) the nature of the oxide fluxes introduced as a bind. Granulometric Composition.—In making the bricks, it is customary to add to the mass a certain proportion of large grains (sometimes up to 10 mm. in diameter). The object of this was to prevent flaws, or incipient cracks, which might tend to spread easily in a fine- grained and homogeneous mass. But, on the other hand, the expansion which accompanies the transfor- mation of the quartz into silica tends to provoke flaws the more easily in proportion as the grains are of larger size. A just medium must be kept, and grains of 5 mm. would appear to satisfy all requirements. It is also indispensable to have a high proportion of very finely-ground quartz. This is a condition that is often misunderstood. In a previous paper, the authors stated that the rate of re-crystallisation of silica increases in proportion to the amount of very fine quartz present. The reason for this is that the strength of the brick at high temperatures is due to the forma- tion of a network of tridymite resulting from the tem- porary solution of the quartz, and its subsequent crystallisation in the less soluble form of tridymite. The viscous magma in which this dissolution is effected attacks the grains of quartz only very slowly and super- ficially. An examination of the thin sections cut from silica bricks proves that, under ordinary conditions of firing, this softened zone is only one-hundredth part of a millimetre thick. Grains below 0-03 mm. in diameter will dissolve completely, and assist greatly in forming the network. On the other hand, the grains left on a No. 200 sieve (4,900 meshes per sq. cm.) are almost inactive in this respect. It is highly necessary that, in the first baking of the brick, at about 1,400 degs. Cent., this network should be well developed; other- wise at high temperatures, e.g., in steel furnaces, it will partially dissolve in the magma on account of the increasing solubility of the silica with the rising tem- perature. If, for instance, this network represents only 10 per cent, of the sum total of silica, the 2 per cent, of lime added will make 20 per cent, of its weight, and will be enough to melt it completely. The large grains of silica then float in a more or less liquid glass; hence the brick loses its firmness, and collapses under its own weight, forming a granular semi-plastic mass. This defect may sometimes be observed in the arch of steel furnaces, when an insufficient proportion of fine quartz has been used in making the brick. In order to ascertain the exact proportions of impal- pably fine material required, the authors prepared test bricks, using, as the finely-dried ingredient, the slimes from gold mining (freed from their impurities by wash- ing with acids), and substituting for the large grains crushed quartzite of a kind easily affected by heat. The resulting mixture was passed through a sieve (four meshes per sq. cm.), so that the largest grains might measure 4 mm. square. All the medium-sized grains produced by the crushing were added, with the excep- tion of a small amount of fine powder, which was added to the slime. The amount of lime used was 2 per cent., and the grinding was done by hand. The firing was carried out in an ordinary brick kiln, which baked the brick in five days, the temperature being limited to that of cone No. 19—1,500 degs. in theory, but between 1,400 and 1,450 degs. in point of fact—because experi- ment has shown that the point of fusion of the cones varies by 50 to 100 degs. Cent., according as they are heated slowly or quickly. With these test pieces, the authors compared bricks of similar make and composition, except that a quan- tity of rather finely-powdered quartz (but not impal- pable) was substituted for the slimes. This powder was obtained by sifting through a No. 100 sieve, the finest portions of the crushed quartz furnishing the coarse ingredients of the mixture. In other words, the 0-01 mm. grains were replaced by those of 0-1 mm. diameter. The results are tabulated as follow: — Composition of mixtures. 75 crude quartzite 25 impalpable 2 lime 75 crude quartzite 25 fine 2 lime 25 crude quartzite 75 impalpable 2 lime 25 crude quartz 75 fine 2 lime Table I. Density. Linear (-------- Resistance in kilogs. In the cold.