182 SCIOPTICON MANUAL, 



AN ECONOMICAL FORM OF GAS MOLBEK FOR Till 

 LIME LIGHT. 



BY J. B. KNIGHT, SECBKTABY FBAWKLIN INSTITUTE. 



" In the summer of 1875 the Franklin Institute determined 

 to put in a pair of holders of considerable capacity, for 

 oxygen and hydrogen, so as to avoid the necessity of 

 preparing the gases on each occasion that they were to be 

 used, and other inconveniences in the use of bags and 

 press-boards in connection with the lime-light. As it was 

 desirable to use as great economy as was consistent with 

 effectiveness and durability, the design shown in the accom- 

 panying illustration was adopted, as covering these points. 



"Fig. 50 is a sectional and Fig. 51 a perspective view, a 

 represents a wooden tank or tub, 4 feet in diameter, and 5 

 feet high, made of cedar wood, and hooped with iron in the 

 usual manner ; b represents the holder, made of No. 10 

 galvanized iron, and is 4 feet diameter by 5 feet high. The 

 roof or top, c, is conical in shape, rising on each side at an 

 angle of about 30, and is attached to the sides of the holder 

 18 inches below the top edge, thus forming a receptacle for 

 water, to act as a weight to produce the required pressure 

 when the gas is being used. 



" In the centre of the holder, and extending its extreme 

 height, is placed the tube d, passing through and fastened 

 by a water- and gas-tight joint to the roof c, and being held 

 firmly in the centre, at its lower end, by the four braces n. 

 The holder is given additional stiffness by the diagonal 

 braces m, which, however, may be dispensed with in holders 

 of this size or smaller. From the centre of the bottom of 

 the wooden tank rises a bar or post of 1-inch round iron, 

 passing through the tube d, and reaching to the ceiling of 

 the room, thus forming a simple and almost frictionlesa 

 guide for the holder in its vertical movements. 



