392 PROCEEDINGS OF THE AMERICAN ACADEMY 



If, on the other hand, the case is one of the division of precipitates, 

 the anthracene and its solvent may be made to pass the filter, after 

 the water has run through, by adding a little alcoliol to overcome the 

 repulsion between the solution and the water which (ills the pores of 

 the filter, the precipitate wliich stays behind being washed iirst with a 

 solvent of anthracene, and then, if necessary, with alcohol followed by 

 water ; or, if the vacuum filter be used (either [laper or asbestos, ac- 

 cording to the circumstances of the case), both liquids leave the 

 precipitate and traverse the filter together. 



In general, I prefer benzol as the solvent for anthracene, but some 

 advantage may be gained in special cases by a proper clioice of sol- 

 vents. Thus, in removing intermixed sulphur from precipitated 

 sulphides, both the anthracene and the sulphur may be dissolved in 

 carbon disulphide in a single operation. 



The ready volatility of anthracene, at a temperature very near its 

 melting point, 213° C, makes it easily separable in cases when to 

 remove it by a solvent is not advisable. The treatment of a solution 

 of anthracene, for example, with strong sulphuric or nitric acid, is apt 

 to produce carbonaceous or gummy residues. In such cases it is well 

 either to heat precipitate and filter directly, or to first remove them 

 from the crucible by means of a solvent for anthracene, then evaporate 

 this and raise the heat gently until the anthracene has vanished. The 

 purification of precipitated baric sulphate, by dissolving it in hot, strong 

 sulphuric acid, and reprecipitating by dilution, is a case in point ; and 

 one, too, in which the reversed filter may be used with great advan- 

 tage. It may be remarked, in passing, that, if one does not happen to 

 possess a platinum rose, and does happen to have at disposal a per- 

 forated crucible, a very fair reversed filter may be improvisetl of the 

 crucible, a piece of glass tubing, and a rubber stopper, the last being 

 fitted to the crucible, and the tube passed through nearly to the 

 perforated bottom. 



At every point in the preparation and use of the anthracene filter. 

 I have found the manipulation peculiarly easy. 



