Author: Digby, W P;Fairthorne, R B
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Digby, W P;Fairthorne, R B
The Department of Scientific and Industrial Research has just issued, through H.M. Stationery Office, a volume of its special reports on the mineral resources of Great Britain. It deals with the geological relations, nature and uses, and mineral, chemical and physical properties of ball clays, that is to say, of those plastic "transported" clays which, when fired in an oxidising atmosphere to the temperature of certain pottery ovens approximately 1,150 deg.-1,200 deg. C.-have a white or nearly white colour. They are formed by the decomposition of felspathic rocks, by natural agencies. In this decomposition, silicates such as the felspars break down, and the products ultimately undergo hydration with the formation of the hydrated silicate of aluminium, kaolinite, and, in many cases, mixtures of hydrated oxides. Where these products are found resting in the parent rock, the clays are termed residual; where they have been transported and deposited elsewhere, they are known as transported clays. The china clays of Cornwall are typical examples of the former; the ball clays discussed in this memoir are characteristic examples of the latter. Dr. Alex Scott
The preliminary report by Mott, Hay and Anderson, consulting engineers, of Westminster, to the Ministry of Transport regarding a proposed road bridge over the Forth at Queensferry has been sent to the local authorities for consideration. The report recommends that the bridge be constructed about a mile dwnstream from the railway bridge, the cost being estimated at £5,570,000 or £6,110,000, according to the route selected for the north approach. A bridge of the suspension type and having a main span of 2,400 ft. with a minimum clearance of 150 ft.-the same as the Forth Bridge-is recommended. The report states thathe present railway bridge was completed in 1889 and was located at the narrowest part of the river, advantage being taken of the rocky island of Inch-Garvie for the site of one of the main piers. It therefore occupies the best position in this stretch of the river. The bridge consists of a main span of 2,400 ft., with a minimum clearance above H.W.O.S.T. of 150 ft. This clearance is the same as that of the Forth Bridge, but while in the case of that bridge the clearance rapidly diminishes under the cantilevers, in the proposed bridge the clearance is maintained under the whole span. The side spans are each 1,040 ft. with clearance above H.W.O.S.T., diminishing from about 150 ft.
At first glance it may appear somewhat absurd to talk to Structural Engineers, or, indeed, any engineer, about welding or the high temperature treatment of modern industrial metals; most members of the engineering profession are more or less familiar with the theory and main principles governing the use of one or other of the half dozen fusive agents now universally employed by the specialist, but one finds quite commonly that an impression exists that welding has positive and well-defined limitations, or that its employment is only possible in certain classes of work and in relation to the union of certain metals. This prejudice is so widespread that it may be well at, the outset to assert without qualification that, in mechanical repairs and reconstructions and in the recreation of any of the industrial metals, there is practically no limit to its application. The idea, no doubt, had its origin in the unfortunate experience a certain number who have been the victims of incompetent operators, who have either failed to do what was required to be done or have employed an unsuitable process or fusive agent, with the inevitable result that the unit or member treated has lost efficiency or been irreparably damaged. C.W. Brett