GENERAL CONCLUSIONS 259 



if any, washing the filter thoroughly, add 50 cubic centimeters of 

 25 per cent, ammonium chlorid solution and ammonia until alka- 

 line, then hydrochloric acid until the precipitate just dissolves. 

 Cool, dilute to about 250 cubic centimeters, and add 50 per cent, 

 sodium thiosulfate solution, drop by drop, until the solution is 

 colorless, adding in all 20 cubic centimeters ; cover with a watch- 

 glass, boil half an hour, filter, wash back into the same beaker, 

 and dissolve in boiling hydrochloric acid; reprecipitate exactly 

 as before, after adding two cubic centimeters of a 10 per 

 cent, ammonium phosphate solution. Wash 20 times with five 

 per cent, ammonium nitrate solution, and ignite to constant 

 weight. For the second precipitation ammonium thiosulfate may 

 also be used, but it is not necessary. 



The greatest difficulty to be overcome in the execution of 

 this method in the case of natural phosphates is the error pro- 

 duced by the presence of fluorin; hence it is necessary to heat 

 the substance for a long time with sulfuric acid to insure the 

 complete removal of fluorin before beginning the separation of 

 the aluminum phosphate. 



An attempt to overcome this source of error by adding an 

 alkaline acetate before boiling with thiosulfate gave no satisfac- 

 tory result. 



Estimation of Ferric Oxid. The determination of ferric oxid 

 is made as follows: Dissolve one gram of the substance in 20 

 cubic centimeters of sulfuric acid, dilute, filter, washing the filter 

 thoroughly, and if any organic matter is present add a little potas- 

 sium chlorate and boil until chlorin is expelled. Reduce the iron 

 with zinc, filter, and titrate at once with potassium permanganate 

 solution, one cubic centimeter of which equals 0.0025 gram of 

 ferric oxid. 



222. Separation of Alumina from Iron by Phenylhydrazine. 

 This method of separation was proposed by Hess and Campbell 

 and elaborated by Allen. 19 It is based on the reduction of the 

 iron by a sulfite and the precipitation of the alumina by phenyl- 

 hydrazine. 



223. General Conclusions. It is evident from the foregoing 



19 Journal of the American Chemical Society, 1899, 21 : 776. 

 Journal of the American Chemical Society, 1903, 25 : 421. 



