258 ANALYTICAL CHEMISTRY. 



neutralize 7.6 c.c. of the acid, then 24 c.c. of water have to be added 

 to every 76 c.c. of the acid in order to obtain a normal solution. 

 Normal sulphuric acid contains 48.91 grammes of H 2 SO 4 , and normal 

 hydrochloric acid 36.37 grammes of HC1 per liter. 



These normal solutions can be made conveniently by diluting either 30 c.c. 

 of pure, concentrated sulphuric acid of sp. gr. 1.84, or 130 c.c. of hydrochloric 

 acid of sp. gr. 1.16 to 1000 c.c. The solutions thus obtained are yet too con- 

 centrated and are adjusted as described above. 



Other methods of determining the exact standard of normal acids depend 

 upon the precipitation of 10 c.c. of the sulphuric acid solution by barium 

 chloride, or of 10 c.c. of the hydrochloric acid solution by silver nitrate, and 

 weighing the precipitated barium sulphate or silver chloride. Ten c.c. of 

 normal sulphuric acid give 1.1736 gramme of barium sulphate, and 10 c.c. of 

 normal hydrochloric acid 1.43 gramme of silver chloride. 



A third method depends on the formation of, and the weighing as, an 

 ammonium salt. Ten c.c. of either acid are neutralized (or slightly super- 

 saturated) with ammonia water. The solution is evaporated in a previously 

 weighed platinum dish over a water-bath, the dry salt is repeatedly moistened 

 with alcohol, and finally dried in an air-bath at a temperature of 105 C. 

 (221 F.) for about half an hour. Ten c.c. of normal sulphuric acid give of 

 ammonium sulphate 0.6592 gramme, and 10 c.c. of normal hydrochloric acid 

 of ammonium chloride 0.5338 gramme. 



Normal alkali solution. A normal solution of sodium carbonate 

 may be made by dissolving 52.92 grammes (one-half the molecular 

 weight) of pure sodium carbonate (obtainable by heating pure sodium 

 bicarbonate to a low red-heat) in water, and diluting to one liter. 

 This solution, however, is not often used, but may serve for standard- 

 izing acid solutions, as it has the advantage of being prepared from a 

 substance that can be easily obtained in a pure condition, which is 

 not the case in preparing the otherwise more useful normal solutions 

 of potassium or sodium hydroxide, both of which substances contain 

 and absorb water. 



The solutions are made by dissolving about 60 grammes of potas- 

 sium hydroxide or 50 grammes of sodium hydroxide in about 1000 

 c.c. of water, titrating this solution with normal acid, and diluting it 

 with water, until equal volumes of both solutions neutralize one 

 another exactly. 



The indicators used in alkalimetry are chiefly solution of litmus 

 or phenol phtalein, only a few drops of either solution being needed 

 for a determination. 



Whenever carbonates are titrated with acids, or vice versa, the 

 solution has to be boiled towaid the end of the reaction in order to 



