468 PRACTICAL ORGANIC CHEMISTRY 8 cm. of water. The constant pressure stream of oxygen is delivered to the apparatus through the side-arm B, and any excess from the cylinder escapes around the outside of the outer tube and through the hole C. When the appara-tus is in use there should be a small but regular excess of bubbles escaping through the liquid and out at C. The potash in A serves to remove any traces of carbon dioxide that may remain in the oxygen. The side-arm B is connected by a length of narrow-bore pressure tubing to a small open-ended manometer D. This rubber tubing, and all the rest employed up to the point V, have previously been impregnated with paraffin wax by immersing the lengths of tubing in paraffin wax boiling under reduced pressure. By these means the wax is driven into the pores of the tubing, which is rendered quite impermeable to the passage of gas through its walls. The orifice of the tube is usually found to be blocked with wax, and after removal of the obvious
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