Manchester Memoirs, Vol. xlviii. (1904), No. 11. 7 



test it is necessary to work the apparatus with some pure 

 dilute sulphuric acid before igniting the escaping hydrogen, 

 and that the tube should previously be heated to redness 

 in front of the drawn out portion on which the mirror is 

 to be deposited. A small piece of platinum wire gauze 

 encircles the tube extending from the edge of the flame 

 to within i^ mm. of the wet tissue paper, which is kept 

 cool by a flow of cold water over it. 



It is also of advantage to use 3 rather than 5 amperes, 

 from the fact that this current can more readily be 

 obtained, and with less loss, from the ordinary electric 

 light wires of a town supply. In Manchester, where the 

 voltage is about lOO, the 3 amperes can be obtained 

 simply and conveniently by fixing two wires, A and B, 

 shown in the accompanying Fig. i, along a strip of wood, 



^^^6ro\ 



}M>i 



iw 



Fig. I. 



attaching a series of holders for filament electric lamps 

 between them ; any number of lamps can then be put in 

 parallel till the desired amperage is obtained, the lamps 

 themselves thus acting the part of the special plugs used 

 by the Committee for adjusting the electric light supply 

 for their apparatus. I find that one 50 and two 32 candle 

 lamps, when put in parallel between the wires A and B, 

 raised the amperage to three, whilst it required four 

 50 candle power lamps so placed to give 5 amperes. 

 The dots on the disjoined wires shew how the lamps are 



