§ 37. EVAPOEATIOX. 27 



covered with one of the large watch-glasses now so much 

 used for this purpose. The flask with the funnel in its 

 mouth is better for the solution of carbonates, since fresh 

 quantities of acid can be conveniently added from time to 

 time. When the solution is finished, carefully rinse the 

 funnel or watch-glass into the flask or beaker. 



Heat is most conveniently applied to a mixture of sub- 

 stance and solvent with the aid of the water-bath, or sand- 

 bath, in making solutions for quantitative purposes, and 

 often in qualitative analysis also. When it is necessary 

 to boil the mixture of substance and solvent for a consid- 

 erable time, and the solvent is more or less volatile, it 

 is best to connect the flask with the loioer end of a Lieb- 

 ig's condenser ; the vapor of the liquid as it is condensed' 

 flows back into the flask, and it is unnecessary to renew 

 the solvent until it is quite saturated. See § 39, c. 



EVAPORATION. 



37 • A liquid may be evaporated either to get rid of a 

 superabundance of water, that makes the solution too di- 

 lute, or to expel an excess of acid, or for the purpose of 

 weighing what it has in solution. In the first and second 

 cases, the operation may be performed in porcelain dishes, 

 unless the solution is strongly alkaline. 



a. In the third case, if the quantity of the liquid is 

 large, it may be evaporated to a small bulk in a porcelain 

 dish, and then carefully transferred to a platinum dish or 

 crucible. Or the original solution may be put into the 

 platinum dish in small quantities at a time ; if, however, 

 the solution contains free chlorine, or nitric and hydro- 

 chloric acids together, it must be evaporated in a porcelain 

 dish until no more fumes of chlorine are evolved ; the 

 residue may then be transferred to the platinum vessel, 

 and the evaporation continued. 



When a cpnsiderable quantity of a liquid is to be evap- 



