to the Estimation of Arsenic^ etc. 



401 



Table II. 



Aso0 3 

 taken 

 grm. 



0-0499 

 0-0499 

 0-0499 

 0-0501 

 0-0997 

 0-0997 

 0-0997 

 0-1001 

 0-1496 

 0-1496 

 0-1502 

 0-1994 

 0-1001 



o-iooi 



K 3 FeC 6 N e 

 grm. 



9 

 10 



10 



12 



4 



3 



KOH 



grin. 



1-25 



1-25 



1-25 



1-25 



1-25 



1-25 



1-25 



1-25 



1-25 



1-25 



1-25 



1-25 



4- 



4- 



Vol. 

 of 

 sol. 

 cm 3 



100 



75 



75 



75 



100 



90 



90 



100 



110 



110 



110 



125 



75 



75 



As 2 3 

 found 

 grm. 



0-0502 

 0-0499 

 0-0501 

 0-0500 

 0*0999 

 0-0993 

 0-0993 

 0*0998 

 0*1492 

 0-1496 

 0*1502 

 0-1994 

 0-0998 

 0-0998 



Error 

 grm. 



+ 0-0003 

 ±0-0000 

 + 0-0002 



—o-oooi 



+ 0-0002 



— 0-0004 



— 0-0004 



— 0-0003 



— 00004 

 + 0-0000 

 + 0-0000 

 ±0-0000 

 -0-0003 



— 0-0003 



(1) 

 (2) 

 (3) 



W 



(5) 



(«) 



(?) 



(8) 



(9) 



(10) 



(ID 

 (12) 



(13) 



(14) 



ting free ammonia, and about 100 cubic centimeters of the 

 magnesia mixture are added. After settling, the ammonium 

 magnesium arseniate is filtered off on asbestos, and washed 

 with faintly aminoniacal water. The filtrate is strongly acidi- 

 fied with dilute sulphuric acid, and titrated with permanganate. 

 As Griitzner* has shown, during the titration of large 

 amounts of ferrocyanide by permanganate, a precipitate of 

 K 2 MnFeC 6 ]N 6 often forms by the action of the manganese 

 sulphate, which is formed by reduction of the permanganate, 

 on the unchanged ferrocyanide. This precipitate slowly clears 

 up as more permanganate is added, clearing up entirely as the end 

 point is reached, but it tends to cause high results, on account 

 of the difficulty in noting the end point exactly. It was found, 

 in connection with the present work, that by titrating in the 

 presence of a large amount of sulphuric acid, the formation of 

 this precipitate is prevented. The titration may safely be 

 made in the cold in the presence of ten per cent of sulphuric 

 acid, and this amount will generally be sufficient to prevent the 

 formation of the precipitate. 



Determination of Antimony. 



A solution of antimony trichloride was made up by dissolv- 

 ing pure antimony trioxide in hydrochloric acid, and diluting 

 to a definite volume with the addition of sufficient hydrochloric 

 acid to prevent the formation of the basic salt; the standard 

 of this solution was determined by titrating with standard 

 iodine. 



*Chein. Centralblatt, 1902, I, 500. 



Am. Jour. Sci.— Fourth Series, Vol. XXIX, No. 173. -May, 1910. 

 27 



