1(3 Mr. T. Bayley on the Analysis of Alloys 



in which ammonia is estimated by Nessler's method, was em- 

 ployed. Dilute standard solutions of pure nickel and cobalt 

 haying been carefully prepared, a measured quantity of cobalt 

 solution was placed in the cylinder, and the nickel added from 

 a burette until the neutral point was reached. It is difficult 

 bv this method to distinguish the exact point of neutrality, but 

 easv to determine that the colour-coefficient of nickel with 

 regard to cobalt lies between 3*1 and 3*2. That is to say, if a 

 quantity of cobalt in solution be mixed with a solution con- 

 taining 3*1 times its weight of nickel, the cobalt colour will 

 slightly predominate in the mixture, which w T ill have a reddish 

 tinge ; while if a solution containing 3*2 times its weight of 

 nickel be added, the nickel colour will be slightly in excess 

 and the solution will have an olive-green tinge. It is only 

 with dilute solutions containing not more than about 2*5 

 grams of the metals per litre that it is possible to determine 

 the coefficient with this accuracy. 



I now sought for some method of indicating more exactly 

 the neutral point. After several attempts, it was found that 

 the addition of ammonium carbonate to the solution of the two 

 metals affords a means of determining whether the slightest 

 excess of either metal is present. 



If we take 25 cubic centims. of solution containing '03125 

 gram of Co, and add to this 39*25 cubic centims. of solution 

 containing '098125 gram of nickel, the resulting liquid appears 

 perfectly colourless. If w r e now dilute the mixed solutions to 

 100 cubic centims., and transfer 25 cubic centims. of that so- 

 lution, containing '0078125 gram of cobalt and '02453125 

 gram of nickel, to a tall glass jar, add 25 cubic centims. of 

 the solution of ammonium carbonate, described hereafter, and 

 then dilute to 150 cubic centims., the result is a liquid of deep 

 purple colour. If we repeat this experiment, using in the first 

 instance '03125 gram of cobalt and '099375 gram of nickel, 

 the colour of the 150 cubic centims. is not purple, but of a 

 distinct blue colour. The ammonium carbonate for this pur- 

 pose must be neutral, as the excess of either base or acid 

 destroys the delicacy of the reaction. 



The solution of neutral carbonate, (NH 4 ) 2 C0 3 , was prepared 

 as follows : — A few ounces of the commercial carbonate having 

 been dissolved in w r ater, 10 cubic centims. of the solution were 

 neutralized by standard solution of sulphuric acid. The quan- 

 tity of NH 3 in the 10 cubic centims. was found to be '085 

 gram. The quantity of C0 2 in an equal quantity of the solu- 

 tion was found to be, in two experiments, '348 gram and '350 

 gram (mean '349 gram): the amount of C0 2 required to form 

 the neutral carbonate with '085 gram of NH 3 being '110, it 



