METHOD OF HESS 233 



alumina. In every case it is necessary to dissolve the precipi- 

 tate and determine the phosphoric acid in the regular way. 

 .Hess proposes the following method for carrying out the acetate 

 process of separation: 



The mineral phosphate should be dissolved in hydrochloric 

 acid and the solution made up to such a volume as shall contain 

 in each 50 cubic centimeters one gram of the original sub- 

 stance. This quantity of the solution is diluted with two or 

 three times its volume of water to which a drop of methyl orange 

 solution ( 1:100) is added, and ammonia added with constant 

 stirring until the solution is just colored and still reacts slightly 

 acid. Without taking any account of the precipitate which is 

 produced by this approximate neutralization of the solution, there 

 are added 50 cubic centimeters of acid ammonium acetate which, 

 in one liter, contains 250 grams of commercial ammonium acetate. 

 The acidity of the solution is due to an excess of acetic hi the 

 commercial salt. The temperature is carried to 70 and the pre- 

 cipitate produced immediately separated by filtration, washed 

 four times with water below 70, and again dissolved in dilute 

 hydrochloric acid. The solution is mixed with 10 cubic centi- 

 meters of a 10 per cent, ammonium phosphate solution and again 

 almost neutralized as described above, and 25 cubic centimeters 

 of the ammonium acetate solution added and warmed to 70. 



The precipitate obtained is once more dissolved and precipita- 

 ted as above described, and is then collected upon a filter, washed 

 ignited and weighed. The residue after ignition is dissolved in 

 the crucible by heating with a little concentrated hydrochloric 

 acid, and washed into a beaker. Any silicic acid present is sepa- 

 rated by filtration, ignited, weighed, and subtracted from the 

 total weight of the precipitate. To the filtrate is added ammonia 

 to diminish the acidity, but not sufficient to produce a precipitate, 

 and the clear solution is mixed with 30 cubic centimeters of the 

 ordinary ammoniacal citrate solution and 15 cubic centimeters of 

 magnesium mixture, and the precipitation of the ammonium mag- 

 nesium phosphate hastened by stirring with a glass rod. 



It is advisable to make the filtrate from the third precipitation 

 slightly ammoniacal and to boil it for a long time. If the opera- 



