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Page:Popular Science Monthly Volume 90.djvu/488

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472

��Popular Science Monthly

��Making a Practical Fluoroscope at Home

��M

��ANY electrical experimenters pos- apparatus such as Tesla,

��sess

��or high frequency apparatus, a large spark-coil, or a static machine, which may be used very well for X-ray ex- periments with only a few accessories. The high cost of the most important of these accessories, the X-ray tube and the fluoroscope, has caused many amateurs to defer, not without reluct- ance, work in this most interesting and instructive field.

It is impossible to make an X-ray tube in the ordi- nary shop or labo- ratory, but it may now be purchased at a very reason- able price. In or- der to secure the best results, care should be taken to select a tube designed especial- ly for use with the particular type of apparatus to be used. There is considerable dif- ference in the de- sign of tubes for the diff'erent types of apparatus. A tube made for use upon a static ma- chine may give

���Frame and pyramid for cutting out the side lights from the fluorescent screen

��very poor results upon a coil or for other purposes, and last only a short time. It is best to get a tube with some form of vacuum-regulating device, as it great- ly increases its usefulness and life.

A fluorescent screen or fluoroscope may be constructed in the laboratory, and may be used equally well with any form of apparatus or tube. To make the fluorescent screen, the fluorescent substance is mounted upon any suit- able supporting surface, such as card- board, in an even continuous layer, so that the rays act through the support and excite the active substance.

A great deal of experimenting has been done in order to ascertain just what substances are fluorescent, and which possess this property in the highest degree. Perhaps the substance best suited for the use of the average

��experimenter is calcium tungstate. This is sometimes found in a sufficiently pure state for use in the natural mineral scheelite, or it may be purchased from a reliable chemist, or made in the lab- oratory. Great care should be taken in order to secure a good crystalline variety.

In order to prepare calcium tung- state (CaW04), in the laboratory, 294 parts, by weight, of sodium tungstate, (Naa WO4) ; III parts-of calcium chlor- ide, (CaCl2); and 59 parts of common salt, sodium chloride, (NaCl) are thor- oughly mixed. The commercial, chem- ically pure sodium tungstate should first be pulverized and heated in an air bath to about 110° C. or 225° F. until the water of crystallization has been driven off", and the salt is thoroughly dry. The calcium chlor- ide and salt should also be pulverized and dried at about the same tempera- ture. This should be done before weighing the chemicals.

The mixture is placed in a cruci- ble and heated in a blast lamp until The crucible cooled, and extracted by

��a furnace or with

it is thoroughly fused.

is then very gradually

when cold, the mass is

dissolving out the sodium chloride with

water, which leaves a mass of calcium

tungstate crystals. These are separated

from the liquid by filtering, washed

well with water to remove any trace

of the chloride, and thoroughly dried.

These crystals should be sifted through

a sieve with a mesh of about 30 to

the linear inch, and preserved for use

in a well stoppered bottle.

Another method of preparing this salt is to precipitate the calcium tung- state from a solution of sodium tung- state in water, with calcium chloride or nitrate. The precipitate is removed by filtering, thoroughly washed, dried and mixed with about twice its

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