18 Analysis of Alloys containing Copper, Zinc, and Nickel, 



If the Cylinders, after the addition of tho ammonium car- 

 bonate be allowed to stand, the differences of tint disappear in 

 :i few hours, and a uniform deep purple-red tint is produced. 

 This is caused by the cobalt absorbing oxygen from the air 

 to form the double compounds of cobalt and ammonia. A 

 small quantity of a sulphite destroys the reaction, as it changes 

 the tint to a deep brown. Thiosulphates and some other re- 

 ducing-agents do not act in this way. 



These experiments lead to the conclusion that the colour- 

 coefficient of nickel with regard to cobalt is 3*16 in all cases, 

 or, in other words, that the tint of nickel and cobalt solutions 

 is independent of the acid radical in combination with the 

 metals, and depends only upon the metal in solution. 



It is evident that nickel and cobalt may be estimated by 

 means of this reaction. As an example of its application to 

 this purpose, I give the following account of the manner in 

 which small quantities of nickel may be estimated. 



The nickel must be dissolved in an acid and the solution 

 diluted to any convenient quantity, e. g. 50 or 100 cubic cen- 

 tims. Into each of three cylinders '0078125 grin, of Co as 

 CoCl 2 is placed. This amount of cobalt is afforded by 6*25 

 cub. centims. of the standard CoCl 2 solution. Calling the 

 cylinders No. 1, No. 2, and No. 3, we place in No. 1 -024531 

 grm. of nickel in solution, and in No. 3 '0248458 grm. To 

 the three cylinders we then add 25 cubic centims. of the stan- 

 dard ammonium carbonate. Cylinder No. 2, which contains 

 only cobalt solution and ammonium carbonate, is then made 

 up nearly to 150 cub. centims., and No. 1 and No. 3 are filled 

 up to that quantity. Cylinder No. 1 has then a purple tinge, 

 while cylinder No. 3 has a blue tinge. By adding from a 

 burette the solution whose strength we wish to determine to 

 No. 2 until its tint is intermediate between No. 1 and No. 3, 

 we make with great accuracy the required determination. In 

 all cases the cylinders should be held, whilst under compari- 

 son, with their lower extremities at some inches distance 

 above a sheet of white paper. Three experiments that by no 

 means reached the highest limit of accuracy, gave the follow- 

 ing results : — 



Ni in solution. Ni found. 



'02469 grm. (1) '02425 



„ „ (2) -02475 



„ „ (3) -02500 



•02466 = mean. 



It is evident that a similar plan of estimating cobalt would 

 be still more accurate on account of the higher colour-effici- 

 ency of that metal. 



