132 Proceedings of the Royal Irish Academy. 



lution obtained by mixing strong solutions of nickel and cobalt is not 

 grey, but reddish brown in colour. 



Having so far demonstrated the complementary character of the 

 two metals, I next endeavoured to find in what proportions they must 

 be mixed in order to neutralize each other. For this purpose a tall 

 glass cylinder (150 c. c. capacity), in which ammonia is estimated by 

 Nessler's method, was employed. Dilute standard solutions of pure 

 nickel and cobalt having 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 

 by this method to distinguish the exact point of neutrality, but easy 

 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 containing 3"1 times its weight of 

 nickel, the cobalt colour will slightly predominate in the mixture, 

 which will 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 neu- 

 tral 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 c. c. of solution containing -03125 gram of cobalt, 

 and add to this 39"25 c. c. of solution containing "098125 gram of 

 nickel, the resulting liquid appears perfectly colourless. If we now 

 dilute the mixed solutions to 100 c. c. and transfer 25 c. c. of that 

 solution, containing -0078125 gram of cobalt, and -02453125 gram 

 of nickel, to a tall glass jar, add 25 c. c. of the solution of ammonium 

 carbonate, described hereafter, and then dilute to 150 c. c, 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 c. c. is not purple, but of a distinct 

 blue colour. The ammonium carbonate for this purpose must be 

 neutral, as the excess of either base or acid destroys the delicacy of 

 the reaction. 



The solution of neutral carbonate (^114)2 CO3 was prepared as 

 follows. A few ounces of the commercial carbonate having been dis- 

 solved in watei', 10 c. c. of the solution were neutralized by stan- 

 dard solution of sulphuric acid. The quantity of NII3 in the 10 c. c. 

 was found to be -085 gramme. The quantity of CO2 in an equal 

 quantity of the solution was found to be in two experiments -348 

 gram, and -350 gram (mean -349 gram) : the amount of CO2 required 

 to form the neutral carbonate with -085 gram of iNHs being -110, it 

 follows that there was an excess of COo equal to -259 gram in every 

 10 c. c. of the original solution of commercial carbonate. To neu- 



