[Illustration:  Fig. 29.]

132. Q.—­What is the tender of a locomotive?

A.—­It is a carriage attached to the locomotive, of which the purpose is to contain coke for feeding the furnace, and water for replenishing the boiler.

133. Q.—­Can you give examples of modern locomotives?

[Illustration:  Fig. 30.]

[Illustration:  Fig. 31.]

A.—­The most recent locomotives resemble in their material features the locomotive represented in fig. 29.  I can, however, give examples of some of the most powerful engines of recent construction.  Fig. 30 represents Gooch’s express engine, adapted for the wide gauge of the Great Western Railway; and fig. 31 represents Crampton’s express engine, adapted for the ordinary or narrow gauge railways.  The cylinders of Gooch’s engine are each 18 inches diameter, and 24 inches stroke; the driving wheels are 8 feet in diameter; the fire grate contains 21 square feet of area; and the heating surface of the fire box is 153 square feet.  There are in all 305 tubes in the boiler, each of 2 inches diameter, giving a heating surface in the tubes of 1799 square feet.  The total heating surface, therefore, is 1952 square feet.  Mr. Gooch states that an engine of this class will evaporate from 300 to 360 cubic feet of water in the hour, and will convey a load of 236 tons at a speed of 40 miles an hour, or a load of 181 tons at a speed of 60 miles an hour.  The weight of this engine empty is 31 tons; of the tender 8-1/2 tons; and the total weight of the engine when loaded is 50 tons.  In one of Crampton’s locomotives, the Liverpool, with one set more of carrying wheels than the fig., the cylinders are of 24 inches diameter and 18 inches stroke; the driving wheels are 8 feet in diameter; the fire grate contains 21-1/2 square feet of area; and the heating surface of the fire box is 154 square feet.  There are in all 300 tubes in the boiler of 2-3/16 inches external diameter, giving a surface in the tubes of 2136 square feet, and a total heating surface of 2290 square feet.  The weight of this engine is stated to be 35 tons when ready to proceed on a journey.  Both engines were displayed at the Great Exhibition in 1851, as examples of the most powerful locomotive engines then made.  The weight of such engines is very injurious to the railway; bending, crushing, and disturbing the rails, and trying very severely the whole of the railway works.  No doubt the weight may be distributed upon a greater number of wheels, but if the weight resting on the driving wheels be much reduced, they will not have sufficient bite upon the rails to propel the train without slipping.  This, however, is only one of the evils which the demand for high rates of speed has produced.  The width of the railway, or, as it is termed, the gauge of the rails, being in most of the railways in this kingdom limited to 4 feet 8-1/2 inches, a corresponding limitation is imposed on the diameter of the boiler; which in