A small metal box must be secured to hold the pitch.  The illustration shows an iron receptacle.  The pitch is prepared by heating the following materials in these proportions:  pitch, 5 lb.; plaster of Paris, 5 lb.; tallow, 1/2

[Illustration:  Design for the Frame]

lb.  To put it in another way, use pitch and plaster in equal parts with 1/10 part tallow.  See that the pitch and plaster are dry so that the moisture will not cause the pitch to boil over.  Keep stirring the mass so that it never boils.  Melt the pitch first and add the plaster by degrees.

For a piece of repousse such as the frame shown, secure a piece of brass of about No. 18 gauge.  With carbon paper trace the design on the brass.  Place the metal on the pitch bed and work over the outline of the design.  Use the chisel-edged tool and try to make the lines continuous.  When this has been done, heat the pitch slightly

[Illustration:  Working Out The Design]

and place the metal, design down, on the pitch, and with the raising punches work up the shape as desired after the pitch has hardened.  When the desired form has been obtained, turn the metal over and “touch up” any places improperly raised.  The metal will probably be warped somewhat.  To remedy this, place a board on the metal and pound until the metal assumes a flat shape again.  Next drill a hole in the center waste and saw out for the opening, using a small metal saw.  Trim up the edges and file them smooth.  Clean the metal thoroughly, using powdered pumice with lye.  Cotton batting fastened to the end of a stick will make a good brush.  Upon the cleansed metal put a lacquer to prevent tarnishing.  Metal clips may be soldered to the back to hold the picture in place and also a metal strip to hold the frame upright.  These should be placed before the metal is lacquered.

** Finding the Horsepower of Small Motors [238]

A small motor often excites curiosity as to its true horsepower, or fraction of a horsepower.  Guesses in this direction vary remarkably for the same motor or engine.  It is comparatively easy to determine the horsepower put out by almost any machine by the following method which is intended for small battery motors and small steam engines.

Before giving the description, it may be well to know what horsepower means.  Horsepower is the rate of work and a unit is equal to 33,000 ft. lb. per minute, or 550 ft. lb. per second.  That is lifting 33,000 lb. 1 ft. in one minute or 550 lb. 1 ft. in one second.  This may be applied to the problem of finding the horsepower of a motor by fastening a piece of twine about 25 ft. long to the shaft of the engine or motor to be tested in such a way that when the shaft revolves it will wind up the string similar to a windlass.  Place the motor in such a position that the twine will hang freely without touching anything:  out of a high window will do.  Fasten a weight to the other end of the line