CH. V] MAGIC LANTERN WITH ACETYLENE LAMP 129 



212. Connecting the burner to the gas supply. For this a 

 heavy and perfect rubber tube or a flexible metallic tube (fig. 60) 

 should be used and the connections with the supply and with the 

 burner should be tied unless special fittings are present. 



As with illuminating gas, the best light is obtained when the 

 correct amount of gas is delivered at the tip of the burner. If too 

 much gas is flowing the jets will blow, and if too little, there will 

 not be light enough. 



If a tank of compressed acetylene in acetone is used (fig. 7 1 A) , 

 the adjustments must be made at the valve on the cylinder. If one 

 turned this on full head and tried to regulate by the stop-cock at 

 the burner the pressure accumulating in the rubber tube would 

 probably blow the tube from its connections or burst it ( 2 1 2 a) . 



212a. Prestolite tanks supplying acetylene for the Magic Lantern. A 



steel cylinder is packed with asbestos and this is saturated with acetone. 

 Acetylene gas is then pumped into the cylinder and is dissolved by the acetone. 



The tanks are charged under a pressure of approximately 15 atmospheres at 

 i8J-^ degrees centigrade (65 F.) this is 15.82 kilos per square centimeter or 225 

 Ibs. to the square inch. 



The tanks are of various sizes, and their holding capacities, under 15 atmos- 

 pheres pressure, are as follows: 



"A" contains 70 cubic feet of gas, (1982 liters), cost $25.00 



"B" contains 40 cubic feet of gas, (1132.6 liters), cost $18.00 



"E" contains 30 cubic feet of gas, (849.5 liters), cost $15.00 



Motor-cycle tank contains 10 cubic feet of gas, (283 liters), cost $ 8.00 



The burner for a magic lantern requires from one to two cubic feet of acety- 

 lene gas per hour. The motor-cycle tank full of gas will then supply light, for 

 from five to ten hours. It costs less than $1.00 to have the tank recharged, 

 hence, the cost of gas per hour is from 10 to 20 cents. 



It is of importance to know at any given time whether there is gas enough 

 to last for an exhibition or for a number of exhibitions. As shown with the 

 lime light the cylinders are supplied with a gauge showing the pressure of the 

 gas within the cylinder, and from Boyle's law that the amount of a gas in a 

 given space depends on the pressure, it is easy to determine at any time the 

 amount of gas available. It is only necessary to know the capacity of the 

 cylinder under ordinary atmospheric pressure and to multiply that volume by 

 the number of atmospheres indicated on the pressure gauge (see also 156). 



For example, the gauge of a motor-cycle tank (fig. 71 B), shows that the 

 pressure is 12 atmospheres, how many cubic feet of acetylene gas arc avail- 

 able? 



As the tank under 15 atmospheres holds 10 cubic feet of gas its capacity at 

 atmospheric pressure must be 10 -=- 15 = % of a cubic foot. If it holds % of 

 a cubic foot under one atmosphere, under 12 atmospheres pressure it will hold 

 % multiplied by 12 = 8 cubic feet. 



The tank will then supply gas for four or for eight hours of continuous light 

 depending upon the capacity of the burner. 



