A B C of television; or, Seeing by radio; a complete and comprehensive treatise dealing with the theory, construction and operation of telephotographic and television transmitters and receivers; written especially for home experimenters, radio fans and students.. (1929)

Record Details:

Title:
A B C of television; or, Seeing by radio; a complete and comprehensive treatise dealing with the theory, construction and operation of telephotographic and television transmitters and receivers; written especially for home experimenters, radio fans and students..
Date:
1929
Publisher:
New York, The Norman W, Henley publishing co.
Volume:
A B C of television; or, Seeing by radio; a complete and comprehensive treatise dealing with the theory, construction and operation of telephotographic and television transmitters and receivers; written especially for home experimenters, radio fans and students..
Leaf #:
000180
Language:
English
Contributor:
Prelinger Library
Sponsor:
MSN
Coordinator:
Media History Digital Library
Date Added:
July 20, 2022
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SELENIUM CELLS 149 Experimenters may use their own ingenuity in devising other means for mounting selenium. Selenium is found among the rare minerals and is related to both sulphur and tellurium in the periodic table. The source of the metal in this country is in the anode muds of our elec trolytic copper refineries. Only a few tons of it are produced each year and its retail price in large amounts ranges from $1.60 to $1.80 per pound. Experimenters may obtain it from any large chemical supply house and when chemically pure its price ranges as high as $1.50 an ounce. One ounce, however, is sufficient for the construction of a number of cells. The selenium marketed is an amorphous substance taking on the appearance of pitch. It is usually sold in sticks about j/ 2 inch thick and 4 inches long. Pure selenium has a boiling point of 690 degrees C. and an atomic weight of 79.2. Assuming that a proper form has been constructed, we shall proceed with the details of the annealing process to which selenium must be subjected before it will exhibit the light- sensitive properties previously mentioned. At this point the author takes the liberty of quoting the well-known authority Samuel Wein. (See Fig. 51 for set-up of equipment.) "After the selenium has been applied to the surface and a satisfactory coating has been obtained, it is placed in either an oven previously heated to 120 degrees C; or a plain laboratory retort stand about 16 inches high may be used. If the oven is used, the temperature will be much easier to control than with an open flame. "In a few minutes the lustrous black surface will change to a dull gray. It is most important that the temperature be con trolled at this point with great care; since the selenium will crystallize if the temperature is not high enough; if the tem perature is too high, the selenium will collect in drops, being