70 Gooc/i and Browning — Method for the Reduction, etc. 



KI 



H„SO, _ 



Jl:ll 



As a O, 





As 2 : 











taken. 



taken. 



taken 





found 





Erroi 







1 grm. 



10 « 



:mi 3 



0-0383 g 



Till. 



0-0380 g 



Till. 



0-0003 



grm. 



— 



1 « 



TO 



u 



0-03S3 



a 



0-0385 



it 



0-0002 



a 



+ 



0-5" 



10 



<■( 



0-0383 



a. 



0-0384 



it 



o-oooi 



« 



+ 



0-4" 



10 



a 



0-0383 



a 



0-0385 



a 



0-0002 



u 



+ 



0-3" 



10 



CI 



0-0383 



c< 



0-0386 



It 



0-0003 



tt 



+ 



0-2" 



10 



a 



0-0383 



a 



0-0384 



« 



o-oooi 



u 



+ 



0-2" 



10 



a 



0-0076 



(C 



0-0074 



CC 



0-0002 



a 





0-2" 



10 



a 



0-0076 



a 



0-0074 



u 



0-0002 



a 



— 



0-2" 



10 



u 



0-0038 



u 



0-0034 



a 



0-0004 



u 



— 



0-2" 



10 



a 



0-003S 



a 



0-0034 



a 



0-0004 



(( 



— 



concentration. In the following experiments colorless solutions 

 were obtained and, for the sake of comparison with the previous 

 results, these solutions were neutralized and titrated without 

 treatment with sulphurous acid, there being no apparent need 

 for adding it in these cases. 



KI 



taken. 

 0*2 grm. 

 0-2 " 



H„S0 4 [1: 1] 

 taken. 



10 cm 3 

 10 " 



As 2 5 

 taken. 



0-0038 grm. 

 0-0038 " 



As 2 5 



found. 



0-0035 grm. 



0-0035 " 



Error. 

 0-0003 grm. — 

 0-0003 ' " - 



Tt appears, therefore, that the average error of the whole 

 number of determinations (twenty-four) made by this process 

 amounts to rather less than 0-0002 grm. — , falling between 

 extremes of 0*0003 grm. + and 0*0007 grm. — . The entire 

 amount of arsenic pentoxide handled in the twenty-four deter- 

 minations was 3*7852 grms. ; and of this 3*7309 grm. were 

 indicated in the titration as reduced to the arsenious condition. 

 The loss 0*0047 grm. — the entire error of the process — amounts 

 to 013 per cent, of the amount taken. 



Certain experiments were made to see whether the period 

 of evaporation might not be dispensed with by so modifying 

 the process that the entire amount of iodine set free in the 

 action of the sulphuric acid, the arseniate, and the iodide 

 might be reconverted at once by sulphurous acid to the condi- 

 tion of hydriodic acid. The conversion was apparently suc- 

 cessful, but the results of the modification were several per 

 cent below the. truth, indicating that the digestion during 

 evaporation, or the removal of the free iodine, or the combined 

 effect of the two, is essential to the completion of the reduction 

 of the arsenic. 



The process as we recommend it may be summarized briefly 

 as follows : — To the arseniate in solution are to be added potas- 

 sium iodide in excess of the amount needed according to the 

 equation to complete the reduction, and 10 cm 3 of half and 

 half sulphuric acid. The liquid is to be diluted to about 100 

 cm 3 and boiled rapidly (with the precautions of trapping as 



