The temperature required for baking earthenware is 1250 degrees—­1310 degrees, C.,; hotel china, 1330 degrees; hard porcelain, 1390 degrees-1410 degrees.  These temperatures can not be obtained in the above kiln by means of the ordinary Bunsen burner.  If will be necessary either to buy the largest size Bunsen, or make one yourself, if you have the materials.  If you can get a cone which can be screwed into an inch pipe, file the opening of the cone to 1/16 in. diameter, and jacket the whole with a 2-1/2-in. pipe.  The flame end of this burner tube should be about 4-1/2 in. above the cone opening and should be covered with gauze to prevent flame from snapping back.  When lighted, the point of the blue flame, which is the hottest part, should be just in the hole in the bottom of the kiln.  Such a burner will be cheaply made and will furnish a kiln temperature of 1400 degrees, but it will burn a great deal of gas.

A plumber’s torch of medium size will cost more in the beginning, but will be cheaper in operation.  Whatever burner is used, the firing should be gradual, and with especial caution the first time.  By experiment you will find that a higher temperature is obtained by placing a 1-in. pipe 2-ft. long over the lid hole as a chimney.  It would be still more effective to get another iron pail, 2 in. wider than the kiln, and get a down draft by inverting it over the kiln at whatever height proves most suitable. —­G.  L. W.

** How to Make a Small Medical Induction Coil [63]

The coil to be described is 3-1/2 in., full length of iron core, and 3/4 in. in diameter.

Procure a bundle of small iron wire, say 1/4 in. in diameter, and cut it 3-1/2 in. long; bind neatly with coarse thread and file the ends smooth (Fig. 1).  This done, make two wood ends, 1-1/4 by 1-1/4 in. and 3/8 in. thick, and varnish.  Bore holes in the center of each so the core will fit in snugly and leave about 1/4 in. projecting from each end (Fig. 1).

After finishing the core, shellac two layers of thick paper over it between the ends; let this dry thoroughly.  Wind two layers of bell magnet wire over this, allowing several inches of free wire to come through a hole in the end.  Cover with paper and shellac as before.  Wind about 1/8 in. of fine wire, such

[Illustration:  Medical Induction Coil]

as used on telephone generators, around the coil, leaving long terminals.  Soak the whole in melted paraffin and let cool; bind tightly with black silk.

The vibrator is made of a piece of thin tin to which is soldered the head of an iron screw and on the other side a small piece of platinum, which can be taken from an old electric bell (Fig. 2).

Of course, a regulator must be had for the vibrator; this can be accomplished by bending a stout piece of copper wire as shown.  The connections and the base for setting up are shown in the figures.  —­Contributed by J. T. R., Washington, D. C.