1880.] On the Spectra of the Compounds of Carbon, §c. 499 



The Sprengel pump employed differs slightly from those in common 

 use. The reservoir is a globe funnel {a, fig. 5), and the valve formed by 

 a glass rod (b) with a conical termination ground into the neck of the 

 funnel. This rod at its upper end passes into an iron ferule (c), which, 

 by means of a screw and a small frame fixed at the top of the globe, 

 can be raised or lowered at pleasure. A little below the globe the 

 tube expands, and the lower part of the tube enters this expansion, 



and terminates upwards in a narrow tube of platinum, round which the 

 glass is fused. By this means the mercury is continually drawn from 

 the centre of a mass of mercury, and there is less chance of air descending 

 with it. Moreover, as the exhaustion proceeds the part of the tube h, 

 above the level of the fall k, becomes vacuous, and is an effectual trap 

 for any air which may be sucked down with the mercury from the 

 globe. The necessity for such a trap is apparent, for when the pump 

 has been in continued use for two or three days there is always a small 

 bubble of air collected in h. 



vol. xxx. 2 N 



