On the Purification of Mercury by Distillation in vacuo. 25 



of the cistern dc, and terminates at b a little below the tube/. 

 The cistern (d c) is made from a piece of glass tube 1 inch 

 in diameter and from 8 to 12 inches long, with two short 

 pieces of quill-tubing, e and/, sealed into it. The lower end 

 is also securely closed with a cork through which passes a 

 piece of ordinary Sprengel-tube, i, 36 inches long, with a 

 piece of quill-tubing, A, about 24 inches in length fused 

 onto the upper end. The top of this tube is nearly in contact 

 with a. The internal diameter of the Sprengel-tube should 

 not much exceed 1 millim., and the bend at its low r er end is 

 best w r hen not much more than one inch in radius. Instead of 

 india-rubber corks, ordinary corks soaked in melted paraffin 

 or covered with sealing-wax may be used, but the apparatus 

 then loses in flexibility. 



The base of the stand consists of a wooden tray, C D, from 

 which rises a stout board, D E, carrying a shelf, A E, perforated 

 in the centre with a hole of sufficient size to allow the glass 

 bulb to pass through it. In the Physical Laboratory of Uni- 

 versity College the board DE which carries the distiller is 

 fixed to the wall over the mercury table. This renders the 

 tray C D unnecessary. A large cork, F, is bored with a hole 

 of rather less diameter than the tube ab, and the cork is cut 

 in halves. By placing the tube in the position shown in the 

 figure and twisting a piece of copper wire round the periphery 

 of the halves of the cork, the tube is firmly supported on the 

 shelf. The cistern is secured by string which passes through 

 holes in the projecting piece of wood, B. A block of wood 

 may be placed as a support for the end of the tube i. A tin 

 cylinder, slightly notched round the top and covered with a 

 flat tin plate, keeps the bulb surrounded with hot air, whilst 

 a mica window at the side allows the height of the mercury in 

 the bulb to be easily seen. The pipe of the brass ring-burner 

 passes through a hole in the tin case. The diameter of the 

 ring is about half an inch greater than that of the glass bulb, 

 and on the inner side it has a large number of very small holes. 



The constant-level reservoir (fig. 2) is made from a large 

 bottle provided with a tubulure at the side. Into this passes 

 (through a cork if the tubulure be sufficiently wide — if not, 

 cemented in with sealing-wax) a glass tube, K, about 3 inches 

 in length and \ inch in diameter. Its outer end is closed, 

 and into the upper and under sides are sealed two pieces of 

 quill-tubing, I and/ The top of the upper one is open, but 

 the lower (j) is connected with the cistern of the distiller by 

 a narrow piece of india-rubber tubing, mm, about 3^ feet 

 long, enclosed in a canvas tube. By means of an india- 

 rubber (or paraffined) cork the thistle-funnel and small glass 



