METHOD OV LASNE 251 



nia be not added in excess. The mixture is then boiled for five 

 minutes. It is allowed to rest for some moments and then fil- 

 tered still hot. The precipitate is drained upon the filter and the 

 filter and the precipitate in the erlenmeyer washed only once. 

 The precipitate both on the filter and remaining in the erlen- 

 meyer is then redissolved in from 20 to 25 cubic centimeters of 

 hydrochloric acid diluted to one-twentieth and heated to 100. 

 The solution in the erlenmeyer and the wash-waters from the 

 filter are united in an erlenmeyer and treated with 3.5 cubic centi- 

 meters of a 10 per cent, solution of ammonium phosphate. This 

 solution should contain about 53.4 grams of phosphoric acid per 

 liter. There is then 0.187 gram of phosphoric acid in 

 excess, and this condition should be realized as nearly 

 as possible. Ammonia is added until a light precipitate 

 persists which is dissolved with great care in a few drops of 

 dilute hydrochloric acid, in such a manner that the mixture 

 clears up gradually after agitation. This having been accom- 

 plished, 1.5 grams of hyposulfite of ammonia are added, or 10 

 cubic centimeters of a solution of this salt containing 150 grams 

 per liter. The volume of the mixture is completed to about 250 

 cubic centimeters, and afterwards it is carried to boiling, which is 

 continued 30 minutes, the volume of water being kept up by oc- 

 casional additions. At the end of this time the precipitation is 

 easily completed. Nevertheless, in order to have a greater cer- 

 tainty, there should be added, after suspending the boiling for a 

 moment, from four to five drops of a saturated solution of ammo- 

 nium acetate. This salt, which in large quantities dissolves phos- 

 phate of alumina, has no influence in so small a quantity. The boil- 

 ing is then continued for five minutes longer. After allowing to 

 settle for a few minutes the liquor is filtered still hot. The pre- 

 cipitate does not adhere to the walls of the flask and is easily 

 collected upon the filter where it is washed seven or eight times 

 with boiling water. The collected precipitate, after drying, is 

 incinerated and kept at a white heat for 15 minutes in the blow- 

 pipe before weighing. The composition of this precipitate is ex- 

 actly P 2 O r ,Al.;PO 3 . The weight of the precipitate multiplied by 

 0.418 gives the weight of the alumina therein. 



