250 ANALYTICAL CHEMISTRY. 



we may calculate from the volume of soda solution used the weight of 

 sodium hydroxide, and from this the weight of copper which has been 

 precipitated. The operation of volumetric analysis is termed titration. 



Gravimetric methods. While the quantitative determinations by 

 these methods differ widely in some cases, there are a number of oper- 

 ations so often and so generally employed that a few remarks may be 

 of advantage to the beginner. A small quantity (generally from 0.5 

 to 1 gramme) of the substance to be analyzed is very exactly weighed 

 on a delicate balance, transferred to a beaker, and dissolved in a suit- 

 able agent (water or acid). From this solution the constituent to be 



FIG. 28. 



Drying-oven. 



determined is precipitated completely, which is ascertained by allow- 

 ing the precipitate to subside and adding to the clear liquid a few 

 drops more of the agent used for precipitation. The, precipitate is 

 next collected upon a small filter of good filter paper containing as 

 little of inorganic constituents (ash) as possible ; the particles of pre- 

 cipitate which may adhere to the beaker are carefully washed off by 

 means of a camel 7 s-hair brush. The precipitate is well washed (gen- 

 erally with pure water) until free from adhering solution, and dried 

 by placing funnel and contents in a drying-oven, Fig. 28, in which a 

 constant temperature of about 100 C. (212 F.) is maintained. The 

 dried filter is then taken from the funnel and its contents are trans- 

 ferred to a platinum (or porcelain) crucible, which has been previously 



