188 On Tribasic Phosphoric Acid. 



In tin- filtrate from the Bolphide of iron, after proper treat- 

 ment, ii" indication of phosphoric acid was produced by mo- 

 Ivbdic acid Bolution. The residue was carefully dried, mixed 

 with carbonate of soda and potassa, and then fused. 



The washing out of this latter residue of sesqnioxide of iron 

 ]ia«l i" be repeated several times, as it ran very easily through 

 the filter. The residue and filter were then ignited, dissolved 

 in BCl, filtered and precipitated by Nil . I find that in 

 cases where it is difficult to separate the residue completely 

 from the filter paper it is better to ignite the paper than to 

 treat it directly with acid. The residue of sesqnioxide of iron 

 obtained by fusion, as every one knows who has ever made an 

 analysis of iron ores, will not very easily dissolve in acid; by 

 digesting the filter with warm hydrochloric acid, some organic 

 substances will be introduced into the solution which will pre- 

 vent the complete precipitation of iron by ammonia. Sulphide 

 of ammonium will nol effeel a more complete separation. The 

 method itself is very difticull and troublesome, and requires 

 much care ami circumspection. 



The results are a- follow- : 



L.1825 (b)— 1.291] (c)— 1.5425 (d)— -1.0429 



PO, 35.98 35.85 35.88 



I V () ::i.:.:; :; - : -''.' ' 84.87 (32.67) 34..M (32.50) 



I In 29.49 29.78 29.61 



mean PO 35.90 



Fe.O 34.47 

 llo 29.63 



VI. Fusing Method. 

 Tin- substance was heated with three parts of a mixture of 



6 NaO, <<» 

 1— K<>. No 

 for not longer than fifteen minutes over the fiameof a single 

 Bunsen burner. Tb utinated ma-.- was triturated with 



