CHEMISTRY. 105 



ignite to coustaiit -weigiit. The -weight liually accepted must not change even after 

 half an hour's ignition. Upon this reiinirement especial stress must be hiid. I'ure 

 magnesium pyrophosphate does not suffer any loss even after several hours' ignition, 

 nor does a good platinum crucible. To the weighed amount of pyrophosphate add 

 the correction given in the table. Multiplication of the sum by 64 gives the amount 

 of phosphoric acid in the weight taken for analysis." 



As an additional precaution against loss of phosphoric acid, it is rec- 

 ommended to cover the under side of the crucible lid with magnesium 

 hydroxid, igniting it until magnesium oxid is formed and the weight is 

 constant before the precipitate is ignited. 



The direct estimation of citrate-soluble phosphoric acid, B. B. 

 EOSS {Jour. Amer. Ghem. Soc, 1(! [1894), Wo. 5, pp. 304-308).— The 

 essential features of the article were presented in a paper before the 

 Association of Official Agricultural Chemists at its meeting in August, 

 1893.^ The method proposed is as follows: 



"After the completion of the 30 minutes' digestion of the samx)le with 100 cc. of 

 citrate solution, 25 cc. of the liqnid is at once filtered out into a dry vessel, pref- 

 erably into a burette. . . . 



"Bring the aliquot, thus measured, into a digestion llask of 250 to 300 cc. capacity, 

 add about 15 cc. concentrated sulphuric acid, and place the flask on a piece of gauze 

 over a moderately brisk flame. 



"Within about 8 minutes the li(iuid will have become quite concentrated and 

 will begin to darken appreciably and at the same time Ibaming will commence, 

 but will occasion no trouble if an extremely high or a very low flame be avoided. 



"After a further lapse of 3 or 4 minutes the foaming ceases and the contents of 

 the flask appear quite black; about 1 gm. of mercuric oxid or metallic mercury is 

 now added and the digestion continued over a high flame. 



"The operation can be readily completed within less than half an hour, and, in 

 many cases, within 25 minutes, a clear and almost colorless li([uid being obtained. 



"After cooling, the solution is washed into a beaker, ammonia is added in slight 

 excess, the solution acidifled with nitric acid, and the regular molybdate method 

 followed, after addition of ammonium nitrate. 



"In case as large an amount as 50 cc. (corresponding to 1 gm. of the sample) of 

 the filtrate from the citrate treatment is employed, 10 cc. of strong sulphuric acid 

 is at first added and the digestion conducted in a flask of 350 to 500 cc. capacity; 

 after the contents of the flask liave blackened and the foaming has progressed con- 

 siderably, the flask is removed from the flame and 15 cc. more of sulphuric acid is 

 added and the flask and contents heated with a low flame for 2 or 3 minutes; 

 mercuric oxid is next added and the digestion is completed as before described." 



The results obtained by this method in a series of determinations by 

 R. E. Blouin agree well with those obtained by the "difference" or 

 official method. The use of the (Tunning modification of the Kjeldalil 

 method proved impracticable on account of excessive frothing 



Some sources of error in our methods of determining potash in 

 fertilizers and G-erman potash salts, IST. Kobinson {Joi(r. Amcr. 

 (Jhem. ^Soc, 16 {1894), No. 0, pp. 364-372). — In this paper, read before 

 the World's Congress of Chemists at Chicago, sources of error in the 



'See Proceedings of the Tenth Annual Convention of the Association of Official 

 Agricultural Chemists, U. 8. Dept. Agr., Chemical Division, Bui. 38, p. 16 (E. S. R,, 

 5, p. 510). 



