APPARATUS. 327 



Chloride of Sodium Standard Solution. Dissolve 

 forty-four grains pure nitrate of silver in 3,000 grains 

 of distilled water; employ a clear white glass bottle 

 and set the same in the sunlight for eight or ten hours. 

 A dark brown or black precipitate will probably form ; 

 when this settles to the bottom, filter into a clean bot- 

 tle, decanting carefully so as not to disturb the sedi- 

 ment; 200 grains of this standard solution should equal 

 one grain of chloride of sodium. Before being put to 

 practical use the solution must be tested. 



Solution of Chromate of Potash is made by saturat- 

 ing three or four ounces of distilled water; an excess 

 of potash remaining undissolved is not objectionable. 



To Test the Standard Solution.. Procure a nice 

 clean lump of " rock salt," crush, and select of the 

 cleanest, ten or fifteen grains ; powder roughly and dry 

 with care, using but gentle heat. When thoroughly 

 dry, dissolve two grains in two hundred grains of dis- 

 tilled Avater, and of this measure fifty grains into a 

 wine-glass, add a little water and one or two drops of 

 the potash solution. Fill the burette and tritate. The 

 addition of the first drops of silver to the salt solution 

 may be followed by the appearance of a red precipi- 

 tate, but on stirring with the glass rod this will re- 

 dissolve ; continue the addition of the silver little by 

 little, stirring well after each addition, until the further 

 delivery of the silver is followed by a permanent pre- 

 cipitate imparting a red color to the contents of the 

 wine-glass. This finishes the test, and if the standard 

 solution is of the proper strength, the burette will 



