for the Distillation of Mercury in a Vacuum. 371 



" bumping ,J and spirting which are so noticeable when mer- 

 cury is distilled under the ordinary atmospheric pressure. 



The rate of distillation is mainly dependent on the capacity 

 of the bulb A. We have generally worked with a bulb 

 rather smaller than that described above, because it is easier 

 to blow it of sufficient thickness. As the still is automatic 

 in its action and needs no attention the quick distillation of 

 a large quantity of mercury is not a point of much importance. 

 It has frequently happened that the distillation has come to 

 an end during the night, both the reservoir and the bulb being 

 discovered nearly if not quite empty. This, however, has oc- 

 casioned no inconvenience ; it is only necessary to introduce 

 more mercury into the reservoir and from thence into the bulb. 

 This can be done without extinguishing the burner. The 

 stopcock J is closed and the tap K is opened. Mercury is then 

 poured through the funnel L. The stopcock F is now opened 

 very gradually, so that cold mercury may not suddenly rush 

 against the hot glass, until the bulb is half full, when the stop- 

 cock J is closed again. A piece of rubber- tubing is now attached 

 to K, and air is sucked out until bubbles begin to rise through 

 the mercury in the reservoir, when K is shut ; after the lapse 

 of about half an hour the stopcock J is opened. When a dis- 

 tillation has been finished and the apparatus is not further 

 required for the present, it may be left standing with the 

 stopcock J closed, and the end F dipping into mercury or 

 otherwise sealed ; it can then be started again at any moment. 

 To empty the still, F is closed and the apparatus is carefully 

 tilted so that the mercury remaining in C may flow into the 

 chamber D. If now the end F be cautiously unclosed air will 

 enter the apparatus through the empty limb C, 



When this apparatus is at work in a dark room the re- 

 markable phenomenon of the " flashing " of mercury is 

 observed. It is seen in the condensation-chamber D. As the 

 mercury liquefies flashes of green light are produced, which 

 exhibit the spectrum of mercury. It would seem that this 

 is an electrical effect arising from friction between mercury 

 and glass. We have noticed that it is enormously intensified 

 when one of the dischargers of a Wirnshurst machine is 

 brought near the chamber D. Under these circumstances the 

 entire chamber becomes illuminated with a magnificent green 

 light. 



The apparatus may also be conveniently employed for 

 observing the electrical discharge through mercury-vapour at 

 different temperatures. For this purpose the ascending 

 column of mercury in B and the descending column of mer- 

 cury in are used as electrodes. One terminal from the coil 

 dips into the mercury in the reservoir H, the other into the 



