CONTACT BREAKS Mechanical, devices for automatically " mak ing " and." breaking " the current flowing. through the primary winding of an induction coil (which see). Several forms of contact breaks are in use, the most popular being the hammer, electrolytic, and motor-mercury breaks. The first-named con sists of a metal spring carrying a soft iron head and pressing against a platinum point which completes the circuit when no current is passing through the coil ; but when the current is switched on the soft iron core becomes a magnet, attracts the block of soft iron, and draws the metal spring from the platinum point,, thus " breaking " contact. The metal spring, or " hammer " rapidly vibrates, " making " and " breaking " contact while the coil is working. In the electrolytic break, the current is com pleted by a platinum point projecting from a porcelain cylinder immersed in an electrolyte.
When the current is turned on, electrolytic bubbles immediately form round the metal point and break the circuit; the bubbles disperse, and the contact of the platinum with the water again completes the circuit. The rapidity with which the bubbles form and disperse makes the electro lytic break a highly efficient one. The motor mercury break consists of a jet of mercury rapidly revolving in a sealed chamber with two or more strips of metal fixed in the sides. When the jet strikes a metal strip the current flows through the coil; when the metal is passed the contact is broken.
Contact breaks make and break the flow of electricity through the coil from a few hundred to several thousand times a minute. In X-ray work an efficient contact break is of the highest importance.