190 



necessary to subject the crucible to several successive heatings and 

 treatment with strong hydrochloric acid in order to remove all of the 

 iron absobed in a single fusion. 



In order to determine whether this amount of iron is what might 

 be considered merely a "trace" or whether it is sufficient to make an 

 appreciable difference in the results of a quantitative analysis, several 

 determinations were made. A platinum crucible was heated to constant 

 weight after it had been subjected a number of times to the treatment 

 just mentioned. A clay fusion was then made and the product removed 

 by the aid of 20 per cent hydrochloric acid. The heating and treat- 

 ment with the acid was then repeated until no further change was 

 observed. The combined solutions of ferric chloride was reduced with 

 stannous chloride, excess of mercuric chloride added, and the amount 

 of iron determined by means of a standard solution of potassium 

 dichromate. Some of the results obtained are as follows: 



Weight of platinum crucible (from previous fusion) after successive 

 heatings over an ordinary burner: 



25.0089 25.0089 25.0090 25.0089 

 Same crucible after successive heatings of fifteen minutes each 

 over a Meeker burner: 



25.0097 25.0097 25.0095 25.0097 

 After treatment with the acid and complete removal of the iron: 

 25.0089 25.0090 25.0090 25.0089 25.0089 



A fusion of a mixture of 0.5 gram of clay and 2.5 grams of sodium 

 carbonate was then made and the product removed by the aid of the 

 acid. Successive heatings over the Meeker burner, each followed by re- 

 moval of the iron present, left the crucible weighing as follows: 

 25.0099 25.0097 25.0099 25.0103 

 After removal of the iron successive heatings gave 



25.0089 25.0084 25.0088 

 After further treatment with the acid and successive heatings, the 

 weights ran as follows: 



25.0084 25.0083 25.0084 25.0081 25.0081 25.0082 

 The total amount of iron oxide found by titration with the potassium 

 dichromate was 0.00459 gram. 



