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The Kinematograph Year Book.
UNIVERSAL FILM CEMENT.
Acetone . . . . . . . . . . . . . . 3 oz.
" Amyl acetate . . . . . . . . . . ... 2. oz.
Glacial Acetic acid . . . . . . . . . . ' . . 2 oz.
Shake well before using. Tins cement will stick either ordinary or nonflam film, and some workers find it possible to use it without scraping the lap, though this is not recommended as a general rule.
GROUND GLASS VARNISH FOR ELECTRIC LAMPS.
Dip the lamps (which should be small and of the vacuum type) in the following solution, which must be made up by adding the various constituents in the order stated : —
Commercial ether Gum sandarac
Gum mastic .. .. -..
Benzole
Do not add the benzole until the gums are completely ether, and on no account use heat for the solution, or let the 'ether come near to a naked light. Cork up tightly when not being used. The lamps must not be warm when dipped, or the varnish coating will dry bright on the glass instead of with a matt finish.
1 pint.
2 oz. . i oz.
I pint.
dissolved in the
MATT SOLUTION WITH WATER BASE.
Use a cold, saturated solution in water of Epsom salts, dip lamps and hang up to dry in a warm place. This matt surface stands heat fairly well, but is removed at once by washing.
WASHING THE GEARS.
Dust, pieces of metal, and other obstacles are attracted and stick to the gear, in time forming hard cakes which render the working jumpy and far from easy. It is advisable occasionally to clear these gears by soaking well in kerosene, paraffin, or benzine.
THE RATIO OF GURRENT TO RESISTANCE IN A CIRCUIT.
Divide the voltage of the supply by the amperes required, and the result will give the resistance in ohms. Conversely, if the supply voltage is divided by the resistance in ohms, the result will give the current in amperes flowing through the conductor. The above facts form a part of what is known in electrical parlance as " Ohm's Law." The equivalent electrical formula are :
Let V stand for voltage or potential difference. ,, C , ,, current. „ R ,, resistance
V V .
Then R = — and C = — C B
When calculating out resistance for an arc lamp circuit (D.C.) on the above formula it must be remembered that the arc itself possesses a back voltage varying from 35 to 50 or more volts according to the current taken For kinematograph projection purposes this back voltage may conveniently be reckoned as 45. Thus the rule for computing resistance in the case of a kine, arc will be : Deduct 45 from the line voltage (represented as " V " in the above formulas), and proceed to apply " Ohm's Law" :
" V-45 R == — , etc. C
where " V " still represents total line voltage