490 Gooch and Phelps — Separation of Arsenic from Copper. 











Table I. 

















Mg 2 As 2 



7 



Error 



in terms 



of arsenic. 



No. 



CuS0 4 



H 2 KAs0 4 



MgMx 



Theory 



Found 



Error 





grin. 



cm 3 . 



cm 3 . 



grm. 



grm. 



grm. 



grm. 



(1) 



2 



0-2 



25 



0*0015 



0-0015 



o-oooo ± 



0-0000 + 



(2) 



2 



0-2 



25 



0-0015 



0-0015 



0-0000 + 



0-0000 + 



(3) 



2 



0-2 



25 



0-0015 



0-0015 



0-0000 ± 



0-0000 + 



w 



2 



1 



25 



0-0077 



0-0086 



0-0009 + 



0-0004 + 



(5) 



2 



5 



25 



0-0386 



0-0415 



0-0029 + 



0-0014 + 



(6) 



2 



10 



50 



0-0766 



0-0798 



0-0032 + 



0-0015 + 



(?) 



2 



50 



50 



0-3830 



0-3922 



0-0092 + 



0-0044 + 



(8) 



2 



50 



100 



0-3830 



0-3910 



0-0080 + 



0-0037 + 



(9) 



2 



50 



50 



0-3830 



0-3957 



0-0127 + 



0-0061 + 



(10) 



2 



50 



25 



0-3830 



0-3952 



0-0122 + 



0-0059 + 



(11) 



2 



50 



50 



0-3830 



0-4120 



0-0290 + 



0-0140 + 



(12) 



2 



50 



50 



0-3830 



0-3960 



0-0130 + 



0-0063 + 



tion. That the copper found here was not hydroxide or basic 

 salt precipitated upon dilution from the ammoniacal solution 

 is shown by the results of experiments (9) to (12), in which 

 the precipitate gathered in the same manner as the previous 

 ones was washed w T ith mixtures of strong ammonia and water 

 — 1 : 8 in experiments (9), (10), and (12), and 1:5 in experi- 

 ment (11). In experiments (11) and (12) the precipitate 

 was rinsed by decantation with faintly ammoniacal water, then 

 with ammonia and water (1 :8) before transferring to the filter. 

 The results make it probable that copper is held in combina- 

 tion in the residue as an arseniate and not as some other com- 

 pound of copper precipitated from the ammonical solution by 

 the water used in rinsing the precipitate. 



In Table II are recorded results obtained by dissolving and 

 reprecipitating the first precipitate. In these experiments a 

 solution of potassium dihydrogen arseniate was run from a 

 burette into the solution of copper sulphate and magnesia 

 mixture in a platinum dish, the precipitate was transferred to 

 a weighed crucible, and, after rinsing once with distilled water 

 made faintly ammoniacal, was dissolved in hot hydrochloric 

 acid, 1 : 4. For convenience in handling the solutions the filtra- 

 tion was made into a beaker inside an evacuated bell-jar rather 

 than into the usual filter flask. After cooling and adding 

 ammonia nearly to neutrality the solution was poured with 

 stirring into an abundance of magnesia mixture kept con- 

 stantly ammoniacal. The precipitate obtained in this way was 

 gathered on the asbestos felt used for the first filtration, the 

 first portion of the filtrate being employed in each case to 

 remove the last portions of the ammonium magnesium arseni- 

 ate from the platinum dish. After rinsing, all traces of 

 reagents from the precipitate vvith distilled water made faintly 



