COMPRESSED air has such a wide application in experimental work and in so many of the arts that it may not be amiss to point out thl possibilities of ordinary bicycle sUfpplies in this line of work. Co nsiderin g its cost, lightness, and simplicity, the ordinary ten-c8nt bicycle pump is a remarkable piece of apparatus. Ii we desire a moderate supply of compressed air to operate, for example, an air brush or a torch-it is only necessary to solder a bicycle valve to a suitable tank and connect our pump. But, you say, how are we to get the air out of the tank? In Figs. 1 to 4 is shown the method of converting a bicycle valve into a needle valve^and an excellent needle valve, too, because when it comes to holding air it is hard to beat a bicycle valve. It will retain air for months. The valve in Fig. 1 is drilled at the base of the threaded portion, and is “provi de d with a small brass tube, fitted into the drilled hole and securely soldered. The cap is drilled through the top and threaded for a screw, which, when screwed far enough down, pushes the little valve stem down and thus lets the air escape. A very small leakage may occur around the rubber gasket in the cap, but this is negligible, as it occurs only when the air is being drawn. If cutting threads is an inconvenient operation, procure an ordinary nipple and spoke. File off the top of the cap, drill a hole in its top, fit on the nLpple and secure it with solder. The resulting cap will then be as in Fig. 2. Cut off the threaded end of the spoke and solder on a round cap, so as to form a suitable screw. The somewhat neater valve shown in Fig. 3 may b made by filing off all the threaded portion of the original valve and discarding the cap entirely. The smiall side outlet tube is provided as before, and the nipple is fitted and soldered directly into the top. The regulation of the air supply is very sensitive. lf three ordinary ten-cent bicycle pumps are arI',anged so as to be operated from a crank shaft with a fly wheel, we obtain a small triplex pump of good capacity and very uniform delivery. In such- arrangements it will usually be found more satisfactory to make the delivery from the lower end instead of through the hollow piston rod, in which event the latter mUJst be soldered up and the lower end provided with a suitable outlet tube. Where it is not practicable to have the valve attached to the air tank, solder it to the lower end of the pump, as in Fig. 5. Fig. 6 shows the ordinary bicycle pump changed into a vacuum pump. The cup leather is reversed, the piston rod is closed, and a valve is soldered to the lower end in the position illustrated. It is hardly necessary to remark that such a pump will not produce a high vacuum, but it wiII compare very favorably with the best piston pumps, and will be found useful in many experiments requiring a greatly reduced air pressure. Sometimes tin cans, such as groceries come in, FIG. E. Air apparatus made of bicycle supplies. will serve as air tanls, but if the pressure is rather high choose one having a length of two or more diameters and brace it by running some straight bicycle spokes clear through and soldering them tight at the ends.