Estimation of Minute Quantities of Arsenic in Copper. 293 



It has been shown by Headden and Sadler* that the presence 

 of copper in the Marsh generator is instrumental in holding 

 back the arsenic and our own experience is similar. It is obvi- 

 ous, therefore, that means must be employed for the complete 

 removal of the copper from the arsenic before the solution of 

 the latter is put into the reduction-flask. So far as our experi- 

 ence goes there is no method by which arsenic may be removed 

 from copper easily, and without loss, aside from those methods 

 which depend upon the volatility of arsenious chloride from 

 solution in strong hydrochloric acid, and of such methods 

 we give the preference on the score of rapidity in execution, 

 accessibility of pure materials, and compactness of apparatus, 

 to a process recently developed in this laboratoryf and based 

 upon the simultaneous action of strong hydrochloric acid and 

 potassium bromide upon the salt of arsenic. 



To get the copper into condition for the application of the 

 process of separation from arsenic we find it sufficient to dis- 

 solve an amount not exceeding one gram in nitric acid some- 

 what diluted with water, to add to the solution two or three 

 cubic centimeters of strong sulphuric acid, and to evaporate 

 the liquid until fumes of the sulphuric acid are disengaged 

 abundantly. A single treatment of this sort serves to remove 

 the nitric acid so completely that no interference with the 

 normal action of the Marsh apparatus is apparent' in the subse- 

 quent operation. The residue after concentration is diluted 

 with water to about 5 cm 3 and washed into the distillation flask 

 with an amount of the strongest hydrochloric acid (sp. gr. 1*20) 

 equal to that of the remainder of the liquid. It is desirable 

 that the entire volume of the liquid should not much exceed 

 10 cm 3 . The flask which has a capacity of forty or fifty cubic 

 centimeters, is inclined at an angle of about 45° and joined by 

 means of a pure rubber stopper to a bent pipette which serves 

 as a distillation tube. The lower end of the vertical limb of 

 the pipette dips beneath the surface of about 5 cm 3 of hydro- 

 chloric acid of half strength contained in a test tube which is 

 cooled and supported by water nearly filling an Erlenmeyer 

 flask. A single gram of potassium bromide is introduced, and 

 the distillation (which may be completed in three or four 

 minutes) is pushed nearly to dryness. The flask is washed out, 

 another portion of potassium bromide is introduced, and the 

 first distillate is introduced and redistilled as before excepting 

 that the condensation is this time effected in pure water. This 

 second operation serves merely to hold back traces of copper 

 carried over in the first distillation, but experiment has shown 

 that the addition of the potassium bromide in the second dis- 

 tillation is quite as necessary as in the first, since the bromine 



* Am. Chem. Jour , vii, 342. f Gooch and Phelps. This Jour., xlviii, p. 216. 



