Gooch and Phelps — Separation of Arsenic from Copper. 491 



ammoniacal, 20-5 cm3 , it was dried over a low Bunsen flame 

 until all ammonia was driven off, and then ignited. The 

 weights of the ignited residues obtained after cooling in a 











Table II 

















Mg 2 A 



s 2 7 





Error in 

















terms of 

 arsenic. 



No. CuS0 4 



H 2 KAs0 4 



MgMx 



Theory 



Found 



Error 





grm. 



cm 3 . 



cm 3 . 



grm. 



grm. 



grm. 



grm. 



(1) 



2 



0-2 



25-25 



0-0015 



0-0012 



0-0003 — 



o-oooi — 



(2) 



2 



0'2 



25-25 



0-0015 



0-0009 



0-0006 — 



0-0003 — 



(3) 



2 



1 



25-25 



0-0077 



0-0072 



0-0005 — 



0-0002 — 



M 



2 



1 



25-25 



0-0077 



0-0079 



0-0002 + 



0-0001 + 



(5) 



9 



5 



25-25 



0-0386 



0-0389 



0-0003 + 



0-0001 + 



(6) 



2 



5 



25-25 



0-0386 



0-0383 



0-0003 — 



o-oooi — 



(<) 



2 



10 



25-25 



0-0766 



0-0754 



0-0012 — 



0-0006 — 



(8) 



2 



10 



25-25 



0-0766 



0-0754 



0-0012 — 



0-0006 — 



(9) 



2 



25 



25-25 



0-1931 



0-1927 



0-0004 — 



0-0002 — 



(10) 



2 



25 



100-100 



0-1931 



0-1919 



0-0012 — 



0-0006 — 



(11) 



o 



50 



' 50-50 



0-3862 



0-3867 



0-0005 + 



0-0002 + 



(12) 



2 



50 



25-25 



0-3862 



0-3864 



0-0002 + 



0-0001 + 



(13) 



2 



100 



50-50 



0-7660 



0-7724 



0-0064 + 



0-0031 + 



(14) 



2 



100 



50-50 



0-7660 



0-7694 



0-0034 + 



0-0016 + 



(15) 



2 



100 



100-50 



0-7660 



0-7723 



00063 + 



0-0030 + 



desiccator, indicate that the ammonium magnesium arseniate is 

 essentially free from copper in combination, except where the 

 arsenic is present in amounts as large as three-tenths of a gram 

 or more. For such amounts the second precipitate was dis- 

 solved in hydrochloric acid and reprecipitated by pouring into 

 magnesia mixture after cooling and making nearly neutral. 

 This treatment, as is shown in the results given in Table III, 

 gives the arseniate free from copper, in ideal condition as the 

 ammonium magnesium arseniate. 



Where the amounts of arsenic were very small it was a 

 matter of difficulty to recover the arsenic after solution in 

 hydrochloric acid in such volumes as are necessary in every 

 case where resolution is made — from 100-300 cm3 — although in 

 some cases the solution was made distinctly ammoniacal before 

 pouring into the magnesia mixture, stirred about five minutes 

 to help bring the crystals out of solution and allowed to 



Table III. 













Mg 2 As 2 7 





Error in 













A 





terms of 

 arsenic. 



Xo. 



CuS0 4 



H 2 KAsO 



4 MgMx 



Theory 



Found 



Error 





grm. 



em 3 . 



cm 3 . 



grm. 



grm. 



grm. 



grm. 



(1) 



2 



50 



50- 50-50 



0-3830 



0-3822 



0-0008 — 



0-0004 — 



(2) 



2 



100 



50- 50-50 



0-7660 



0-7653 



0-0007— 



0-0003 — 



(3) 



2 



100 



50- 50-50 



0-7660 



0-7656 



0-0004 — 



0-0002 — 



W 



2 



100 



100-100-100 



0-7724 



0-7726 



0-0002 + 



0-0001 + 



