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342 RICHARDSON'S BLUEBOOK OF PROJECTION
(25) In high intensity arcs the metallic parts of the lamps are close to the very hot light source, and here penciling makes damage.
Inspection of Carbons
(26) Newly purchased carbons should be examined carefully. Inspect the core ends, which should, in each carbon, fill the opening completely. There should be no defects, though an occasional small fault need not cause rejection of a bundle of carbons.
(27) It is manifestly essential to steady light production that carbon cores be continuous, and that they fill their space completely, adhering to its walls tightly. Otherwise short sections may drop out as the carbon is consumed, with disastrous effect upon the screen illumination.
(28) No attention need be paid to small cracks running lengthwise in low intensity carbons. They do no particular harm and are, in a manner, characteristic of the product. It is extremely unlikely that any crack will be found so wide or deep as to cause trouble.
(29) Narrow and shallow cracks around low intensity carbons should be tolerated but circumferential cracks of more than superficial depth may cause a carbon to break while in use. Cracks of any sort in high intensity carbons are a cause for rejection. They are very deterimental to screen illumination. It may be assumed safely, however that all carbon manufacturers compel a severe inspection of their product before it leaves the factory.
Using Carbon Stubs
(30) Although projectionists should burn their carbons as short as possible, it is questionable economy to attempt to make use of carbon stubs by joining them, more or .less imperfectly to whole carbons or other carbon stubs. Several devices* have been perfected for the
*The carbon saver marketed by the Projection Improvement Company is very simple and with ordinary care should last indefinitely. It consists of a metal tipped handle, c, as shown in Fig-. 83, a heavy, hollow, coppercoated steel rod, d, a block of soft wood and certain copper caps, a. They