Tin is the best material to use for the tender, as no great strength is required--indeed it should be made as light as possible. The wheels and axles you must finish in the same manner as those on the engine, and it can be made into a tank to hold an extra supply of alcohol by soldering a piece of tin round the inside and covering it in with another piece cut to shape and fitted with a screw nut to fill by as shown in Fig. 18. Such is the method of constructing a model locomotive which will run without complicated machinery. The boy who has succeeded in following these directions will no doubt be ambitious to try his hand on a more complete model on a larger scale, something like Fig. 20 for instance, which is a side view of a large model locomotive in a finished state. HOW TO BUILD A LARGE MODEL LOCOMOTIVE. In building a large model the first thing to be done is to decide how large you want it. Sketch your model carefully, or, if not able to draw plans, get some one who is to help you. Make your plan the exact size of the model you intend to build, then you can take all the measurements from it and save yourself a lot of trouble and time. Remember, however, that the larger you make the engine the more expensive the castings and materials will be. Should you persevere, however, and by good fortune succeed, you will have a model locomotive that would cost you two or three hundred dollars to buy ready made. If you have a lathe and can turn the wooden models for the castings yourself, use sheet iron for the frame-work, etc., where possible; the total expense will not be so very great. Begin your work in the same way you did on the other model. If you want a bigger engine than the one shown in Fig. 20, there would be no trouble in increasing the measurements, which we are about to give, proportionately, remembering that Fig. 20 is drawn to an eighth-inch scale. DIMENSIONS. Make your dimensions as follows: Length over all, 3 ft. 2 in. Length of bed-plate, 3.5 in. Width of bed-plate, 9 in. Diameter of driving wheels, 8-1/4 in. Diameter of leading wheels, 5-1/4 in. Gauge--that is width of track on which model can run--6-1/2 in. Cylinders, 1-3/4 in. bore by 2-1/2 in. stroke. Length of boiler, including smoke box, 28 in. Diameter of boiler, 5 in. Cylinders of the above dimensions will drive the engine at a high rate of speed, with from 30 to 50 lbs. of steam. DESCRIPTION OF LARGE MODEL LOCOMOTIVES. In Fig. 20, the different parts of the engine are lettered, and it will be well for the boy who desires to make a locomotive like it to compare the following description with the cut, before he does anything else. [Illustration: Fig. 20.]