INORGANIC COMPOUNDS. 177 



which is to be used for the determination, and heat the residue 

 to red heat. Copper sulphate contains 31.87 per cent, of CuO. 



3. DETERMINATION OF WATER OF CRYSTALLIZATION IN 

 COPPER SULPHATE. 



Place in a porcelain crucible a known weight about 0.5 

 to 0.6 g. of copper sulphate, weigh accurately, heat for 

 some hours in an air-bath to 110-115, and continue heating 

 at this temperature until a constant weight is obtained. 

 Copper sulphate loses four molecules of its water of crys- 

 tallization at this temperature, i.e., 28.8 per cent. 



4. DETERMINATION OF CALCIUM IN CALCIUM CARBONATE, 

 CaC0 3 , AS CALCIUM OXIDE. 



Place 0.3-0.4 g. (accurately weighed) of pure calcium 

 carbonate, previously gently heated, in a 150- to 200-cc. 

 beaker, cover with water, dissolve by cautiously adding 

 dilute hydrochloric acid (the beaker should be covered with 

 a watch-glass, which is afterwards to be rinsed off), and 

 dilute with water, so that the beaker is at most one-third 

 filled (or the carbonate may be dissolved in a flask, the solution 

 poured into a beaker, and the flask well rinsed). Heat the 

 solution in the beaker on the wire gauze until it begins to boil, 

 and add about 15 cc. of ammonium oxalate solution. If a 

 precipitate forms, it is dissolved by adding hydrochloric acid. 

 Then, in any case, add ammonia to distinctly alkaline reac- 

 tion, and after several hours of standing best till next day 

 filter, wash the precipitate thoroughly with warm water (the 

 last wash-water should give no turbidity with nitric acid and 

 silver nitrate), dry, and incinerate. Finally heat strongly 

 with the blast-lamp for at least five minutes. After- weigh- 

 ing repeat the heating with the blast-lamp, and heat even a 

 third time until the weighings agree. Test the calcium 

 oxide obtained for calcium carbonate: when covered with 



