LEKOY C. COOLEY. 137 



Disconnection is made at this point always while the as- 

 pirator is still running to prevent the water in the bottle, 

 s, from backing over into the vacuum produced in the 

 filter flask or Other vessel employed. 



For evaporation, a glass funnel is selected whose di- 

 ameter is a trifle less or a trifle more than that of the 

 evaporating dish, and whose stem is six or eight inches 

 long, and bent at right angles, close to the body. Let 

 this funnel be inverted over the evaporating dish and 

 rest ivpon it, (fig. 2), and let its stem be connected with 

 the aspirator by being thrust through the rubber tube 

 at b ; then turn on the water and apply the heat. Air 

 will be drawn into the funnel, entering between its edge 

 and that of the dish and out through the aspirator into 

 the waste-pipe, carrying the corrosive vapors with it. 



Since the edge of the funnel may rest either inside or 

 outside that of the dish with the same result, one funnel 

 will fit dishes of different sizes. One of three inches in 

 diameter for evaporating dishes, and another of one and 

 a half inches for crucibles, are in use. 



With this ventilating funnel strong nitric acid can be 

 evaporated to dryness on the open work-table without 

 inconvenience from its fumes. 



Or a ventilating flask may be used for the same pur- 

 pose. Close a flask with an air-tight stopper pierced 

 with two glass tubes, one reaching well down toward the 

 surface of the liquid within, the other only through the 

 cork (fig. 3). The latter is to be connected with the as- 

 pirator. A rapid current of fresh air will thus be drawn 

 over the surface of the evaporating liquid and with the 

 corrosive vapors off into waste. 



Or, let the cork be pierced with a single tube to con- 

 nect with the aspirator. A partial vacuum will then be 

 formed within, and the evaporation will occur under di- 

 minished pressure and at lower temperature. 



89 



