A crude form of this type of interrupter may be made by heating the end of a test tube in a pin flame, and then blowing on the open end of the tube so as to burst the soft glass and form a small hole. Several such test tubes should be prepared having holes varying from 1/32 to 1/8 of an inch in diameter. The one which gives the best results upon trial is selected for use. A number of holes in a single tube, if not too many or too large in diameter, increases the efficiency and the speed of interruption. The tube should be immersed in a glass jar containing dilute sulphuric acid. One lead electrode is placed inside of the test tube and the other outside. It makes no difference which way the current flows through this interrupter.
The Caldwell interrupter is a modification of the Simon type in which the size of the aperture is made adjustable by means of a pointed glass rod which may be raised or lowered in the hole and the speed of interruption varied. An interrupter of the test tube type as described above may be modified to this form by locating the hole directly in the center of the bottom of the tube and inserting in it a hard glass rod which has been drawn out to a point.
Electrolytic interrupters do not require any condenser connected across the break.
Fig. 41. Construction of Electrolytic Interrupters.
Fig. 41 shows in section more substantial forms of both the Wehnelt and Simon-Caldwell interrupters. The containers are ordinary 5 x 7 inch battery jars. They are fitted with covers made of two thicknesses, C and B, of 3/4-inch wood. The upper piece, C, is 6 inches in diameter, while the under one should fit snugly into the interior of the jar. The wood must be boiled in paraffin to protect it from the action of the acid. A slit is made in the left-hand side of both covers for the passage of a lead electrode, L, 1 inch wide and 1/4 inch thick. The upper end of the electrode is bent over and fitted with a binding post.
Fig. 42. Details of Electrolytic Interrupters.
The mechanism for adjusting the interrupters is the same in both cases. The dimensions are indicated in Fig. 42. A brass yoke, Y, is mounted on the cover in the position shown. A 1/2-inch hole is bored through the upper part of the yoke and a piece of brass tubing, S, 1 inch long soldered in a vertical position in the hole. A 1/4-inch threaded brass rod passes through the tube, 5. A groove is milled in A along its entire length and engages a pin in the wall of S. The rod is thus enabled to slide up and down in the tube but is prevented from revolving. A fiber head, H, is fitted with a brass sleeve or bushing in its center. The bushing should fit tightly into the fiber head and is threaded to fit the rod, A. The electrode may then be carefully raised or lowered by revolving the head. The tube, V, for the Simon-Caldwell interrupter is a hard glass test tube. A 1/8-inch hole is blown in the bottom of the tube. A hard glass rod, G, is drawn out to a point and fastened to the lower end of the rod, A, by means of a short length of flexible rubber tubing, R.
The tube, N, for the Wehnelt break is made from a piece of hard rubber tubing 6 inches long, having a bore of J inch.