160 Austin — Double Ammoniuin Phosphates in Analysis. 



that salt proportionate to the strength of the alcohol employed. 

 This is shown in the accompanying statement. 



So it appears that in washing with ammonium phosphate 

 and alcohol, according to Dakin's procedure, the precipitate 

 of the double ammonium phosphate must be loaded with 

 foreign material to a degree dependent upon the conditions. 

 This error is in the same direction as that introduced by the 

 solubility of the serpentine in nitric acid. With these two 

 sources of error active, the most remarkable thing about 

 Dakin's results is that they happen to agree so closely with 

 mine, the solubility of the serpentine asbestos and the insolu- 

 bility of the ammonium phosphate in alcohol together counter- 

 balancing the deficiency due to imperfect constitution of the 

 double ammonium phosphate. 



As to the experience of Miller and Page^ upon the ammo- 

 nium cadmium phosphate, in consequence of which they 

 concluded not only that my method for the estimation of 

 cadmium is unsatisfactory, but that "asbestos filters should 

 be avoided on account of the solvent action of either ammo- 

 nium phosphate or nitric acid," it is sufficient to direct atten- 

 tion to the fact that their analytical examination of this process 

 is wholly worthless by reason of their use of serpentine asbestos. 



With suitable anhydrous asbestos at disposal, the estimation 

 of magnesium, manganese, cadmium and zinc precipitated as 

 the double ammonium phosphates, according to the directions 

 and with the precautions laid down in the former papers from 

 this laboratory to which reference has been made, is perfectly 

 practicable. Concerning the manganese and zinc phosphates, 

 in particular, it may be reiterated that with a sufficiency of 

 ammonium salt, preferably the chloride, and with an excess of 

 the precipitant present, the precipitation is complete and the 

 phosphate formed of nearly ideal constitution. In the pre- 

 cipitation of the ammonium cadmium phosphate the propor- 

 tions of the reagents must be regulated with care. The use of 

 ammonium phosphate followed by rinsing in alcohol is not 

 only wholly unnecessary but always altogether undesirable. 



* Scliool of Mines Quarteiij, xxii, 391. 



