SOLUTION IN SODIUM CARBONATE 6oi 



chlorid solution. The barium sulfate formed is separated, 

 washed, dried, and weighed in the usual manner. 



(3) Iron and Alumina. To the other half of the solution a 

 little nitric acid is added and boiled to convert any ferrous into 

 ferric iron. On the addition of ammonia the iron and alumina 

 are separated as hydroxids, collected on a gooch, washed, dried, 

 ignited, and weighed as oxids. 



(4) Lime. In the filtrate the lime is thrown out as oxalate, 

 and separated and weighed in the usual way as oxid. One part 

 of CaO is equal to 2.4286 parts of CaSO 4 . 



(5) Moisture. Two grams of the sample are dried to con- 

 stant weight at 80. 



(6) Water of Crystallization. The residue from the above 

 drying is heated to 150, until a constant weight is obtained. The 

 loss represents water of crystallization. 



(7) Carbonates. The carbon dioxid is evolved by the usual 

 process, and calculated to calcium carbonate. 



507. Solution in Sodium Carbonate. Gypsum is also easily 

 decomposed by boiling with a solution of about 10 times its 

 weight of sodium carbonate. The calcium, by this operation, is 

 converted into carbonate and can be collected on a gooch, washed, 

 and estimated as usual, but in this case it will contain all the 

 insoluble matters, from which the lime can be separated by solu- 

 tion in hydrochloric acid. 



In the filtrate from the above separation the excess of sodium 

 carbonate is removed by the addition of hydrochloric to slight 

 acidity, and the sulfuric acid estimated as described in the pre- 

 ceding paragraph. 



Pure gypsum has a composition represented by the follow- 

 ing formula: CaSO 4 .2H 2 O. 



It contains: 



Per cent. 



Sulfur trioxid 46.51 



Lime 32.56 



Water 20.93 



A commercial sample of ordinary gypsum should have about 

 the following composition : 77 



77 Frankland, Agricultural Chemical Analysis, 1883 : 240. 



