172 REPORT— 19U0. 



The work under the tirst head was in progress at the time the former 

 part of the report was published by one of the present writers and Mr. 

 Bailey, and was subsequently carried as far as seemed desirable. The 

 results obtained with moderately strong solutions of bismuth were very 

 unsatisfactory, even in presence of much citric acid and when treated 

 with all the care indicated by our former experience. We then proceeded 

 to detei-mine the major limit of concentration at which good determina- 

 tions can be made. 



Taking 150 c.c. as the most convenient volume for use in the electro- 

 lytic capsules employed, we found that excellent results could be obtained 

 in presence of 2-5 gr. of citric acid, so long as the weight of metal in 

 150 c.c. did not exceed 0'22 gr. With stronger solutions we failed to 

 obtain satisfactory reguline deposits, even when the proportion of citric 

 acid was increased and the current at the commencement of the operation 

 was reduced to 0'005 ampere, so that the rate of deposition should be very 

 slow. 



AVe therefore arrived at the conclusion that 150 c.c. of bismuth solution 

 should not contain more than about 0-22 gr. of metal in the form of 

 nitrate or sulphate, and that 2-5 to 3-0 gr. of pure citric acid suffice 

 to control the deposition, provided the initial current used and acting for 

 some hours be about 0-01 ampere, increased at the end, and for a short 

 time, to 0-15 or 02 ampere. 



Scjiaraiiun uf Bismuth fro)n other Metals. 



Extended experience in the electrolytic determination of bismuth in 

 simple solutions of varying strength led us to doubt that the purely 

 electrolytic separation of the element from other metals would prove satis- 

 factory. The results obtained by the present writers have justified this 

 anticipation. 



The least unfavourable determinations of bismuth in such ndxtures 

 with other metals as would probably be met with in practice were those 

 obtained with cadmium and zinc ; but even in these theoretically favour- 

 able cases it was found that, however feeble the currents used, the deposited 

 bismuth carried down sensible amounts of the much more positive metals. 

 The method of experimenting was as follows : — 



A carefully measured volume of a bismuth-nitrate solution known to 

 contain 6-018 gr. of metal per litre, in the form of nitrate, was placed 

 in a platinum capsule. The special treatment to be applied in each case 

 was then carried out ; pure citric acid added, the solution diluted with 

 water to about 150 c.c, and a current passed through the liquid of such 

 strength (generally 0-01 ampere) as to secure a good reguline deposit of 

 bismuth. The whole of the metal was seldom separated under fifteen to 

 twenty hours, and was hastened at the end by passing a current of about 

 0-1 ampere for a short time. The contents of the capsule were then washed 

 with water and alcohol, and the vessel dried and weighed. 



Of the experiments recorded below, the first three aimed at fixing the 

 degree of accuracy with which bismuth could be electrolytically separated 

 from the particular simple nitrate solution used in presence of citric acid. 

 The citric acid used in work of this kind should be tested for lead, &c., 

 before use, as samples are sometimes met with which contain metallic 

 impurities. The total volume of liquid used was the same in these as in all 

 other cases, viz. about 150 c.c. 



