134 Laboratory Arts 



may again be tested, and if still insufficiently cleaned and 

 purified nothing short of distillation will suffice. 



Many devices are on the market for the distillation of 

 mercury ; many of them doubtless very good, but a six-ounce 

 Jena retort, heated by a Fletcher argand gas-ring, and sur- 

 rounded with an asbestos millboard jacket, produces the greatest 

 yield at least cost, both of apparatus and trouble. The retort 

 is rested on wire gauze, and the asbestos millboard is cut so 

 as to surround the bulb of the retort, and the top is almost 

 covered with a sheet of millboard having two slits or holes 

 about i" diameter pierced through to let the heated gases escape. 

 No cooling arrangements are necessary, but it is necessary to 

 cool down the apparatus before the addition of fresh mercury, 

 and it is advisable not to use more than 3 Ibs. of mercury at 

 a time, as bumping is dangerous to the retort in such case. 

 Of course, the whole of this apparatus is stood meanwhile upon 

 a tray, so that in event of a breakage no loss of metal may occur. 

 Slow distillation with a fairly small flame is the most 

 satisfactory. 



It is a good plan to keep a separating funnel partly filled 

 with concentrated sulphuric acid, into which all laboratory 

 mercury residues are put immediately after use. The mercury 

 drawn off from the bottom of such a funnel is usually in 

 excellent condition, and needs no preparation before use. 



VI. CARE OF LABORATORY IRONWORK. 



The fumes in a laboratory cause considerable annoyance by 

 their effect upon ironwork, which needs almost constant atten- 

 tion in consequence. The usual method is to coat the ironwork 

 annually with Brunswick black, and this is a source of annoyance 

 during the rest of the year to any one who has to use apparatus 

 so treated. Retort stands, clamps and rings, tripod stands, 

 Bunsen burners, and similar appliances must be protected, and 

 it is a matter of importance to choose some method that will 

 give satisfaction to all concerned. 



For the above ironwork, if a black enamel be required, 

 nothing better can be obtained than the <l Eggshell black," 



