CHEMISTRY. 193 



alkaline with ammouia. Indeed, theoretically the correct way is to add 

 the sodium phosphate in excess to the slightly acid solution and then 

 precipitate with ammonia. 



It is not necessary to remove the ammonium salts by ignition before 

 precipitation, as only ammonium oxalate interferes, and this may be 

 removed by redissolving the slightly washed precipitate in a little 

 hydrochloric acid, adding some sodium phosphate and reprecipitating 

 with ammonia. If tliis is neglected the results may be slightly too 

 high. The presence of a certain amount of ammonium salts is indis- 

 pensable to the accuracy of the results. Ammonium oxalate does not 

 hinder the precipitation in the least. For especially small precipitates 

 24 hours must be allowed for complete precipitation, and during the 

 interval the solution should be vigorously stirred several times. The 

 excess of sodium phosphate must not be too small. 



The ignition of the precipitate over the blast lamp, or some similar 

 burner, must continue for at least one-half hour, or until there is no 

 further loss in weight. — c. l. I'ARSons. 



Precipitation of phosphoric acid in the citrate extract of 

 Thomas slag by means of molybdic solution, M. Schmoeger 

 {Chem. Ztg., 20 {IsfJO), No. 51, p. 4!)7).— Two methods were tested. In 

 the first, 50 cc. of the extract was mixed with 50 co. of the citrate solu- 

 tion used in the ordinary citric-acid method and the phosphoric acid 

 precipitated with 25 cc. of magnesia mixture in the usual way. After 

 weighing, the precipitate was dissolved in hydrochloric acid, the solu- 

 tion digested for some time in the water bath, evaporated to dryness to 

 remove silica, and the phosphoric acid again precipitated in the usual 

 way. 



In the second method, 100 cc. of molybdic solution' Avas added to 

 500 cc. of extract and heated 10 minutes in a gently boiling water bath. 

 The yellow precipitate was dissolved on the filter, and magnesia mix- 

 ture slowly added to the neutralized (with HOI) and cooled solution. 



Comparisons of the methods on 8 kinds of Thomas slag are reported, 

 which show that where silica was not removed both methods gave too 

 high results, this being more marked in the case of the molybdate 

 method than of the citrate method. 



An accurate volumetric method for determining phosphoric 

 acid and arsenic acid, A. Christensen {Nord.phann. Tidsskr., 1896, 

 p. 77; abs. in Chcm. Zt;/., 20 {1896), Nos. 42, Repert, p. 153; 50, Repert, 

 p. 171). — Solutions of phosphoric acid or arsenic acid are heated with a 

 mixture of potassium bromate and iodid. The following reaction occurs 

 with phosphoric acid: KBrO:,+0KI + ()H3PO4=()IvH>PO4+6l4-KBr-|- 

 3H2O. The separated iodin is titrated with fifth normal thiosulphate in 

 the usual manner, each 1 cc. of thiosulphate corresponding to 0.0071 

 gm. of phosphoric acid. 



'100 gm. molybdic acid, 400 gm. aninioiiium hydrate 0.96 sp. gr., and 1,500 gm. 

 nitric acid 1.2 sp. gr. 



