Peters — Volumetric Estimation of Copper. 365 



Experiments 33-35 stood six hours before filtering. Experiments 

 36 and 37 stood over night. Copper is separated from more 

 than twice its weight of cadmium, and the results are accurate. 



Separation from Arsenic, in Both Conditions of Oxidation. 



For the separation from arsenic, arsenious oxide dissolved in 

 sodium carbonate, and di-hydrogen sodium arseniate were the 

 forms of arsenic used. The results are accurate and are given 

 in sections G and H of the table. In experiments 38-40 and 

 44 and 45 no nitric acid was added. While the presence of the 

 nitric acid is not necessary for the separation of the copper 

 from the arsenic; still the filtration in the absence of the nitric 

 acid is so slow as to be objectionable. The presence of the 

 nitric acid causes the precipitate to come down in a coarser 

 condition, and in such condition it filters easily and is capable 

 of being washed quickly. 



Separation from Tin, in Both Conditions of Oxidation. 



For the separation of copper from tin a preparation of stan- 

 nous chloride (20 cm3 giving 0*3746 gm. metallic tin by the 

 battery) containing sufficient hydrochloric acid to prevent depo- 

 sition of oxy -salts was used. The solution of stannic chloride 

 contained 1*0 gm. metallic tin to every 10 cm3 , and was used 

 without hydrochloric acid. The results of the work are found 

 in sections I and K of the table. The experiments go to show 

 that while copper may be separated from small amounts of tin 

 as stannous chloride yet there is a limit to the amount of tin 

 which may be present. One-tenth of a gram of metallic tin is 

 the largest amount that can be present, with 0*15 gm. copper 

 oxide taken as the sulphate, without significant error. Practi- 

 cally the same statement can be made of the separation of cop- 

 per from tin taken as stannic chloride. Experiment 57 shows 

 a greater loss of copper when the nitric acid is omitted. 



Separation of Copper from Iron. 



A solution of ferric nitrate was used for the work on the 

 separation of copper from iron. Low results were obtained 

 when a solution of ferrous or ferric sulphate was used as the 

 source of iron. The results of the experiments are recorded 

 in section L of the table, and show that - 20 gm. copper oxide 

 as the sulphate may be separated from 0'2-0*3 gm. iron oxide 

 taken as the nitrate. In experiment 64 a good result was 

 obtained when no nitric acid was present, save that added in 

 combination with the iron. A comparison of experiments 63 

 and 65 shows that it is best to avoid the use of large amounts 



