An air pump for a blowlamp, and particularly suitable for the apparatus described on p. 151, may be made from brass tube l in. in diameter and 6 in. long. Take a thick circular disc of brass of the same diameter as the tube, and drill a conical opening in the side, and also a cross channel to join it as at D; then braze the drilled disc on the end of the tube. File away the surplus spelter, and with emery and oil grind the conical opening true, so that when the metal ball shown is dropped in it will completely close the passage. If any difficulty is experienced in making the ball fit air-tight, line the cone with thin leather; the ball will then act satisfactorily. C is a plug of leather well soaked in oil, and attached to the plunger rod by means of a small nut as shown. When in use, the back pressure exerted on the lower end of the plug causes it to expand on the down stroke, and so closely fit the tube that all the air in it is forced through the outlet D. On the upward stroke commencing the ball closes down the hole at D, and air passes the sides of the plunger as it is drawn upwards.

A screwed cap B made to fit the barrel completes the pump.

Air Pump for Blowlamp.