273. Adjustable Table. Fig. 124. A table that can be raised or lowered is useful. The one shown at D, Fig. 124, is used for the galvanometer of A[pp. 117]. The dimensions are given in the figure. The upright piece, U, is fastened to D with brass screws, not with nails, as these would affect the needle. It is placed at one side of D so that the compass needle placed in the center of D will also be in the center of the wire coils when used in [App. 117]. The table is fastened in any position by a screw-eye, S I, which presses a copper washer, W, against U. S I works through a narrow slot, S, and screws into the back of the galvanometer. By making S longer, the table may be used for other laboratory purposes, if it is joined with some other form of standard.
Fig. 124.
274. Glue Pot. If you have occasion to use glue, you can make a good glue pot out of 2 tin cans, one being placed inside the other. Put ¼ teacupful of glue in the inside can. If you have time, cover it with cold water, and let it soften. If you are in a hurry, cover it with hot water. Set this inside can into the other, in which you have boiling water. Do not let the water boil over. The solder will not melt from ordinary tomato cans, if you keep water in them. Thin the glue with a little hot water until it drips from the brush in drops. Have the glue hot and fairly thin, and apply quickly. Hold the pieces of wood together by pressure until the glue hardens.
275. Paraffine Paper and Cardboard are extremely useful for insulating purposes. The paraffine used in candles will do, if you cannot get it in block form. While ordinary paper will do for simple apparatus to wind about coils, etc., you will find that paraffine paper can be handled very rapidly. To melt the paraffine you should use a double boiler, or one made of a shallow basin set in a pan of water. The water should be boiled. This will melt the paraffine in the basin. Strips of paper just passed through the melted paraffine will become soaked, and the paraffine will quickly harden in the air. Allow thick cardboard to soak for a minute or two, to drive out all the air. This makes excellent washers for electro-magnets. ([See § 119].) To make one piece of this paper stick to another, merely pass a clean hot nail over the two where they lap. To hold coils of wire together, or to wooden bases, use a few drops of paraffine applied with a large hot nail.