for the Distillation of Mercury in a Vacuum. 369 



tance of about 5 centim. from the bulb, is expanded to form a 

 chamber D for the condensation of the mercury vapour ; this 

 chamber is 1 decim. long and 1 centim. wide. The other end 

 of the limb is for convenience bent twice at right angles F, 

 and beneath it is placed a receptacle for the distilled mercury. 

 The movable reservoir H, attached by means of at least 

 1 metre of stout rubber-tubing, known as " pressure " tubing, 

 to E is a large tap-funnel having a capacity at least twice 

 as great as that of the bulb A. It is provided with a tightly- 

 fitting indiarubber cork carrying a small tapped tube K, which 

 projects just below the cork, and a thistle-funnel L which 

 extends to the bottom of the reservoir. The apparatus is 

 supported by a clamp immediately below the chamber D, 

 and it rests on the bend E of the stout limb B. 



Before the still is set in action it must be thoroughly dried. 

 The reservoir H is then filled with dry mercury and raised 

 until the liquid has ascended to the summit of the bulb A, and 

 has commenced to fall over into the limb C. The reservoir 

 is now slightly lowered, and by means of the tap J the flow 

 of mercury is checked until it falls only moderately fast (as 

 in a Sprengel pump) down the limb C. In about five minutes 

 the chamber D will have been exhausted of air. As soon as 

 the sharp " click " of the falling mercury is heard and the 

 descending column in C is almost continuous, the reservoir is 

 lowered until the bulb A is about half full. The reservoir H 

 is now adjusted to act automatically in maintaining a constant 

 level of mercury in the bulb A. The stopcock J having been 

 shut, the bulb is heated and the distillation allowed to proceed 

 for about half an hour until the vapour-pressure of the 

 mercury for the maximum temperature to which the bulb will 

 be raised has been attained. Air is then sucked out of the 

 tube K until bubbles pass up through the mercury, when the 

 tap in K is instantly closed. The tube of the funnel L now con- 

 tains no mercury, the pressure of the air and of the mercury in 

 the reservoir being exactly equal to the atmospheric pressure 

 acting through L. The level of the mercury in the reservoir 

 must now be adjusted until the surface of the mercury in the 

 bulb is distant from the bottom of the reservoir (above J) by the 

 height of the barometric column less the vapour-pressure of 

 mercury for the temperature at which distillation occurs. This 

 temperature having been ascertained, the adjustment may be 

 made after direct measurement of the mercurial column. It may 

 also be effected perhaps more readily by raising the reservoir 

 little by little until on momentarily opening the stopcock J air 

 is observed to bubble through the mercury. As soon as this 

 occurs, the stopcock J is left open. The mercury from the 



