Arsenic Acid, 



157 



ably regular and accurate without the application of an 

 arbitrary correction. This process, moreover, may be shortened 

 by restricting the volume at which heating begins so that the 

 boiling need not be extended beyond five or six minutes. 

 According to this slight modification, the solution of the 

 arseniate is heated in an Erlenmeyer flask with potassium 

 iodide to an amount about 0*5 gram in excess of the amount 

 theoretically required and 10 cm3 of sulphuric acid of half 

 strength in a total volume of between 50 cm3 and 75 0ra \ The 

 liquid is boiled till the iodine vapors are no longer visible in 

 the flask above the liquid, the iodine color in the still hot 

 liquid is bleached by the cautious addition of sulphurous acid, 

 the whole is diluted with cold water, and cooled quickly. The 

 solution is nearly neutralized with potassium hydroxide and 

 the neutralization is completed with acid potassium carbonate. 

 The reduced acid is titrated with iodine after adding the starch 

 indicator. By this procedure the results of the following table 

 were obtained. 





H 3 3 AsO 



H 3 3 AsO 





Volume. 



taken. 



found. 



Error. 



cm 3 . 



gram. 



gram. 



gram. 



35 



0-1559 



0-1559 



o-oooo 



35 



0-1559 



0-1560 



+ 0-0001 



40 



0-1559 



0-1559 



o-oooo 



65 



0-1559 



0-1559 



o-oooo 



50 



0-2495 



0-2499 



+ 0-0004 



50 



0-2557 



0-2449 



— 0-0008 



60 



0-3119 



0-3117 



— 0-0002 



60 



0-3119 



0-3120 



+ 0-0001 



75 



0-3119 



0-3124 



+ 0-0005 



75 



0-3119 



0-3132 



+ 0-0013 



75 



0-3119 



0-3121 



+ 0-0002 



75 



0-3119 



0-3115 



— 0-0004 



75 



0-3119 



0-3124 



+ 0-0005 



