370 Messrs. Dimstan and Dyniond on an Apparatus 



reservoir H will now be automatically supplied to the bulb A. 

 As the mercury distils out of the bulb more rises from the 

 reservoir to take its place, and air enters from the funnel L 

 and bubbles through the mercury in the reservoir into the 

 closed space above. Through this action of the reservoir the 

 level of the mercury in the bulb will remain the same until 

 the whole of the mercury contained in the reservoir has been 

 distilled. 



In order to heat the bulb A the tubes just below it are 

 surrounded by the ring-burner M, which may be a circular piece 

 of metal or glass tubing perforated at regular intervals with 

 small holes ; the flames proceeding from these perforations 

 should be very small, and must on no account be allowed to 

 impinge on the bulb or on either of the tubes. The bulb is 

 now enclosed on all sides so that a hot air-chamber may 

 result. This is best done by cutting a circular disk N, whose 

 circumference is somewhat greater than that of the ring- 

 burner, out of asbestos millboard, incisions being made to 

 correspond with the tubes so that the disk may slide under 

 the bulb and rest on the burner itself. On this disk as a 

 base a cylinder of the same material, or of glass, is placed, 

 the cylinder being wider and taller than the bulb. The 

 cylinder is closed at the top by a rather larger and circular 

 piece of asbestos millboard, in the centre of which a small 

 round hole should be cut. By partially or entirely cover- 

 ing this hole with a small disk of millboard, it is easy to 

 regulate the admission of air to the chamber. The cylinder 

 is prepared from the millboard by thoroughly wetting it and 

 rolling it round a bottle or wooden block of the proper size. 

 When dry the cylinder is removed and secured by twisting a 

 piece of thin copper wire round it. The bulb is thus heated 

 in the air-chamber, and not by direct contact with the flames, 

 and the bulb is effectually protected from the disastrous 

 effects of draughts of cold air. 



The temperature of the air-bath when distillation is pro- 

 ceeding ranges between 200° and 300° C. Since fresh mer- 

 cury is automatically supplied to the bulb the still requires 

 no attention, and may safely be left at work day and night 

 provided that the gas pressure is almost constant. This may 

 of course be ensured by fixing a gas-regulator in the air-bath. 

 We have found, however, that an ordinary Sugg's dry governor 

 introduced between the gas supply and the burner answers 

 the purpose sufficiently well. 



When the still is started for the first time the air-film on 

 the glass is detached and passes away down the liinb C. The 

 distillation consists in continuous evaporation from the 

 liquid surface unaccompanied by actual ebullition, or by the 



