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Rh on to them from heights of 10, 15, and 20 ft. until the tyre deflects under the blows a specified amount without breaking.

Chemical Tests. Each railway company has, in addition to a mechanical testing shop, a well equipped laboratory in which samples of the above materials are analyzed. Chemical tests are not often specified for the materials, beyond limiting the amounts of sulphur and phosphorus in steel, both of which are deleterious. Thus boiler plates must not show more than 0·05 per cent. of either of these elements, but in the case of springs, tyres, and axles, these limits are reduced to 0·035 per cent. Copper firebox plates are specified to contain from 0·25 to 0·55 per cent. of arsenic, which has the valuable property of reducing wear in service.

Trial Trips of Completed Locomotives. Contrary to what might be supposed, new locomotives do not, except under special circumstances, undergo any elaborate tests, such as are usual with large marine or mill engines. An engine built at a railway company’s works is immediately sent out on a trial run of some 20 to 25 miles without a train. During the trial the working of the motion, springs, brakes, injectors and sandgear is noted carefully. The big end and axlebox bearings must run perfectly cool, and there must be no leakages at any of the joints, to which the fittings and mountings on the