10 RESEARCHES UPON ATOMIC WEIGHTS. 



It was shown in our determination of the specific gravity of cadmium chloride, 

 that the salt when prepared in this way contains no ammonium chloride. It 

 is probable that the cadmium chloride contained no basic compound, since no 

 insoluble salt was produced when the chloride was dissolved in water. The 

 aqueous solution of the salt invariably contained a few tenths of a milhgram of 

 black insoluble matter which consisted chiefly of platinum. The presence of 

 this platinum was undoubtedly due partially to sUght attacking of the boat, 

 owing perhaps to contamination of the hydrochloric acid with traces of air. 

 The sHght loss in weight of the boat which resulted in most of the analyses was 

 not sufficient to account for all the insoluble residue, which, therefore, must 

 have had its source, in part, in the original material. Whether the platinum 

 was dissolved from the platinum condenser during the distillation of the hydro- 

 chloric acid, or from the platinum dish during the solution of the cadmium is 

 uncertain. At all events, the temperature to which the salt was heated must 

 have been sufficient to decompose all the platinic or platinous chlorides present, 

 and since the insoluble residue was filtered out and weighed, and corrections 

 applied to the weight of the salt both for the loss in weight of the boat and for 

 the insoluble matter, no appreciable error could have been introduced by 

 the platinum. 



THE METHOD OF ANALYSIS. 



After the salt had been weighed, the boat was transferred to a flask and the 

 salt was dissolved in about 200 c.c. of the purest water. The weighing-bottle 

 was rinsed and the rinsings were added to the solution. Next the solution was 

 filtered into the precipitating flask through a tiny filter to collect the insoluble 

 matter. Filter-paper and residue were then ignited in a weighed porcelain 

 crucible. 



In the preHminary analyses the ratio of cadmium chloride to silver chloride 

 was determined by adding to the solution of cadmium chloride, which had been 

 diluted in the (Erlenmeyer) precipitating flask until not stronger than i per 

 cent, a solution of a slight excess of silver nitrate of very nearly the same con- 

 centration. The flask, which was provided with a ground-glass stopper, was 

 shaken for some time, and was allowed to stand until the solution was clear. 

 Then the precipitate of silver chloride was transferred to a Gooch crucible, after 

 it had been washed by decantation six or eight times with about 150 c.c. of a 

 0.00 1 normal silver nitrate solution, and finally several times with pure water. 

 Needless to say, the operations of precipitation and filtration were performed 

 in a room lighted only with ruby light. The crucible with the precipitate was 

 placed in an air-bath and heated for several hours at 130° to 140° C, and after 

 it had cooled in a desiccator it was weighed. In order to determine how much 

 moisture was retained by the precipitate in each case, it was transferred to a 

 clean porcelain crucible and weighed, then the salt was fused by heating the 

 small crucible, contained in a larger covered crucible, and again weighed. Two 



