It is generally preferable to have the bar taper to a slightly narrower width at its free end, and near this free end it is necessary to solder a small strip of platinum at the point where the end of thumbscrew comes in contact.
"G", "H", "I" and "J" are ventilating holes one inch in diameter and covered by a swinging slide so that the holes can be opened or closed as desired for regulating the ventilation. "K". Is a shelf of brass screen located about five inches from the top and on which the watches and a thermometer are placed in testing.
"L". Is a handle for the purpose of convenience in carrying the box. The front is to be enclosed by a door made in two parts, the upper section of which is glass which will admit of observing the thermometer. Proper adjustment of the thumbscrew and bar makes the box ready for use.
[9.]The Lower Temperature Box.
Fig. 2 shows a box specially made for testing watches in cold. It is constructed of wood and stands about twenty-four inches high without the legs and about eighteen inches square.
A double partition packed with about one inch of sawdust will be most reliable.
The upper half of the box should contain a watertight zinc tank for holding cracked ice and about an inch of space should be left above for circulation of the air.
The chamber for receiving the watches may be about six inches square and supported by a crosspiece and attachment to the front. It should be covered above to prevent particles of ice from falling on the watches which are to be placed on the floor or on a shelf of the chamber, but the sides may be left partly open to improve the circulation of cold air. The door may also be filled with sawdust but does not require glass as the moisture would prevent observation of the thermometer which should be inside for checking up the temperature when the door is opened.
Fig. 2