436 Mr. C. C. Hutchinson on the Separation and 



during ignition ; otherwise reduction of the oxide will occur, 

 and loss by volatilization as the well-known brown cadmium 

 vapour. The filter-paper is saturated with ammonium nitrate 

 to prevent volatilization of the small amount of adherent parti- 

 cles; it is then ignited in the usual way, either upon the lid of the 

 crucible and not in contact with the oxide, or, more conveni- 

 ently, in a smaller crucible : carefully conducted, little or no 

 loss by reduction occurs. The filtrate containing the zinc is 

 evaporated down to a small bulk to drive off the excess of am- 

 monium salts, diluted to a convenient extent, and titrated with 

 a standard solution of sodium sulphide in the usual manner. 



The following examples may be given, to show the success of 

 this method. 10 cub. centims. of solution of each of the pure 

 sulphates containing known amounts were mixed, excess of 

 ammonia added, and their complete precipitation effected by 

 addition of ammonium sulphide in excess. The washed sul- 

 phides were then dissolved in hydrochloric acid, and the solu- 

 tion treated as above described. The following are the results 

 obtained in each instance : — 



grm. 



Cadmium actually present 0*112 



„ „ found 0*117 



Error 0*005 + 



gi'in. 



Zinc actually present 0*065 



„ „ found 0*065 



No- 2. ^ 



Cadmium actuallv present 0*1163 



„ „ " found 0*1239 



Error 0*0076 + 



grm. 



Zinc actually present 0*065 



„ „ found 0*065 



To ensure rigorous comparison in each of the above cases, 

 the amount of each metal present in the 10 cub. centims. of 

 solution taken was directly determined by taking at the same 

 time a corresponding separate quantity of each of the solu- 

 tions : the zinc solution was titrated with sodium sulphide, and 

 the cadmium precipitated as the carbonate, ignited, and weighed 

 as the oxide. 



Other examples could be given, in which the error in the cad- 

 mium-estimation did not exceed 0*5 of a milligramme in 0*112 

 gramme total amount present; the zinc estimations were 

 equally as favourable as the two examples above quoted. In 



