. Elementary and dental radiography . ig. -4. Acid hydrometer. happen if the core were wound with uninsulated wire. If this were donethe current would not follow the windings of the wire at all. but wouldchoose the shorter path of less resistance, passing along the iron core,making a short circuit. ) ( )ver the primary winding is placed a heavyinsulation of mica or vulcanite, and around this is wound more insulatedwire the secondary winding. (Figs. 32 and 33.) There is positively no electric connection between the primary andsecondary windings. The primary current passes through the primary 2S
. Elementary and dental radiography . ig. -4. Acid hydrometer. happen if the core were wound with uninsulated wire. If this were donethe current would not follow the windings of the wire at all. but wouldchoose the shorter path of less resistance, passing along the iron core,making a short circuit. ) ( )ver the primary winding is placed a heavyinsulation of mica or vulcanite, and around this is wound more insulatedwire the secondary winding. (Figs. 32 and 33.) There is positively no electric connection between the primary andsecondary windings. The primary current passes through the primary 2S ELEMEXTARY RADIOGRAPHY winding and into the negative lead wire. But in its passage it has in-duced or created a secondary current in the secondary winding. Coils are rated and designated according to the maximum num-ber of inches of atmosphere the secondary current can be made to the current jumps from one terminal to the other of the secondarywinding, a spark occurs, due to the resistance of the atmosphere to the P n t 4- B. Fig. 25. Fig. 26. Fig. 25. A. movable arm with fulcrum at B. C, electro-magnet. D, break. E, 26. A, piece of ribbon steel. B, point where circuit is broken. C, electro-magnet. flow of the current. When we speak of a coil as, say a 12-inch coil, wemean that the spark gap of that coil is twelve inches long; that its sec-ondary current can be made to jump twelve inches of atmosphere. Thelarger the coil the longer the spark gap. From 6-inch to as high as 40-inch coils are manufactured. From 8-inch to about 18-inch coils are thesizes generally used. The wire of the primary winding is from \2- to 8-gauge; of the sec-ondary from 34- to 29-gaUge. The length of the windings varies accord-ing to the size of the coil, of course. The wire in the primary of a [2-inchcoil is about 100 feet long, in the secondary about 28 miles long. Thewin- in the primary of an [8-inch coil is about [40 feet, and in the sec-ondary 38 miles long. X-RAY MACHIXES 29
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