290 



Mr. Gr. A. Hemsalech on the Origin of the 



furnace. For the better conducting vapours of iron, cobalt,. 

 and nickel could thus be conceived to convey an electric 

 current under the pressure of the small potential gradient in 

 the furnace-tube more easily than the less conducting vapours 

 of zinc, copper, and silver ; the first three metals would 

 therefore be able to emit a line spectrum at lower potential 

 gradients than the last three metals. Thus the inability of 

 the vapours of zinc, copper, and silver to emit a spectrum 

 at the highest furnace temperature can be satisfactorily 

 accounted for by assuming them to possess a low degree of 

 electric conductivity. 



§ 6. Observations on the Spectrum Emission of Metal 

 Vapours in the absence of Electric Actions. 



All the facts observed so far point to electric actions as 

 being the determining factor in the line emission of metal 

 vapours in the high-temperature resistance-tube furnace. 

 It was therefore felt desirable to de\ise a test experiment 

 with a furnace in which electric actions were, if not 

 altogether suppressed, at least reduced to a minimum. After 

 several trials the following type of furnace was constructed 

 which seemed to fulfil these conditions (fig. 2). A graphite 



Fig. 2. . 



+ 



Sectional View of Plate Furnace, 



plate AB, 245 mm. long, 20 mm. wide, and 1*9 mm. thick, 

 is clamped in a horizontal position between two pairs of 

 stout graphite bars which carry the current from the mains. 

 On the middle part of AB, at 0, a small furnace is built up 

 of the small graphite plates a, a', and b: each of these plates 

 is 20 mm. wide, and a, a' are about 20 mm. long each, 

 h somewhat longer. The lower edges of a and o! are cut 



