A small stopcock may be easily made out of two glass tubes and a rubber sleeve. The outside diameter of one tube is smaller than the inside diameter of the other. The end of the smaller tube is softened in the flame of a Bunsen burner and closed. With a file a small slot is cut in the side of this tube. A piece of rubber tubing is fitted over the two glass tubes, as shown in Fig. 164. The smaller tube is not held so tightly by the rubber sleeve as is the larger tube, and it will slide quite readily therein. When the smaller tube is drawn outward, the rubber sleeve covers the slot therein, preventing the passage of liquids or gases through the two tubes. To open the cock, the smaller tube is forced inward, as shown in the sectional view, and the liquids or gases can then flow freely through the two tubes by way of the slot in the smaller tube.

Fig. 160- Stopcock of glass tubing.