A few of the blowpipe-made articles, such, for example, as glass stopcocks, need more careful annealing, and for this purpose a small sheet-iron oven which can be heated to dull redness over a collection of gas burners will serve. Better still, a small clay muffle can be used. In either case, the article to be annealed should be laid on a clean, smooth, fireclay surface, the temperature should be maintained at a very dull red for two or three hours and then reduced steadily until the oven is cold. This cooling should take anything from three to twelve hours, according to the nature of the article to be annealed. A thick article, or one having great irregularities in thickness will need much longer annealing than one thinner or more regular. As a rule, soda-glass will need more annealing than lead-glass. _Drilling Glass._--Small holes may be drilled in glass by means of a rod of hard steel which has been broken off, thus giving a more or less irregular and crystalline end. There are several conditions necessary to enable the drilling of small holes to be carried out successfully:--the first of these is that the "drill" should be driven at a high speed. This may be done by means of a geared hand-drill such as the American pattern drill, although a somewhat higher speed than this will give is even more satisfactory. The second condition is that the pressure on the drill is neither too light nor too heavy; this is conveniently regulated by hand. The third condition is that the drill be prevented from "straying" over the surface of the glass; for this purpose a small metal guide is useful. The fourth condition is that a suitable lubricant be used; a strong solution of camphor in oil of turpentine is perhaps the most suitable. For commercial work, a diamond drill is often used, but this is scarcely necessary for the occasional work of a laboratory. _Larger Holes in Glass._--The method of drilling with a hard steel rod is not highly satisfactory for anything but small holes. When a larger hole, say one of an eighth of an inch or more, is needed it is better to use a copper or brass tube. This tube may be held in an American hand-drill, but a mixture of carborundum or emery and water is supplied to the rotating end. Tube or drill must be lifted at frequent intervals in order to allow a fresh supply of the grinding material to reach the end. In this case, also, a guide is quite essential in the early stages of drilling; otherwise the end of the tube will stray. The speed of cutting may be increased slightly by making a number of radial slots in the end of the tube; these serve to hold a supply of the grinding material.