Manganese as the Pyrophosphate. 243 



surely, according to our experience, by following the method 

 of the experiments of Table Y. The slightly acid solution, 

 containing in a volume of 200 cm3 (in platinum or glass) an 

 amount of manganese not more than enough to make 0*4 grm. 

 of the pyrophosphate, 20 grm. of ammonium chloride and 5 

 to 10 cm3 of a cold saturated solution of microcosmic salt, is 

 precipitated in the cold by the careful addition of dilute 

 ammonia in only slight excess. The mixture is heated until 

 the precipitate becomes silky and crystalline, the whole is 

 allowed to stand and cool a half hour, the precipitate is col- 

 lected upon asbestos in a perforated platinum crucible, washed 

 (best with slightly ammoniacal water), dried at gentle heat 

 and ignited as usual. By this process determinations of the 

 larger amounts of manganese — # 4 grm. of the pyrophosphate 

 — approximate rather more closely to the theoretical values 

 than do those of the smaller amounts — 0*15 grm. In either 

 case the average error should not exceed 0*0010 grm. in terms 

 of manganese. 



