188 Gooch and Austin — Constitution of the 



of the solution, were it not for the fact pointed out by 

 Kichards and Kogers* that the oxide of magnesiurn retains on 

 ignition occluded nitrogen and oxygen enough to increase its 

 weight sensibly. For this reason the nitrate was converted 

 to the sulphate and weighed as such— either by^ evaporating to 

 dryness in a weighed platinum crucible a definite volume of 

 the solution, igniting as oxide, and changing to the sulphate 

 by heating with sulphuric acid ; or, by evaporating the mag- 

 nesium nitrate directly with an excess of sulphuric acid of 

 half strength. In this treatment the excess of acid was 

 removed by heating the platinum crucible upon a porcelain 

 ring or triangle so placed within a porcelain crucible that the 

 bottom and wails of the inner crucible were distant about one 

 centimeter from the bottom and walls of the outer crucible. 

 The excess of acid is easily removed in this way, and the outer 

 crucible may be heated to redness without danger of breaking 

 up the magnesium sulphate. The results of this work, taking 

 O = 16, Mg = 24-3, 1ST = 14-03, S = 32*06, are given in the 

 accompanying table. 



Table I. 



MgS0 4 obtained by- 



MgS0 4 obtained 



Theoretical amount 



converting ignited MgO 



directly from 



of MgO in 



into the sulphate. 



50 cm3 Mg(N0 3 ) 2 . 



MgS0 4 . 



grm. 



grm. 



grm. 



0-5748 







0-1924 



6-5739 







0-1923 





0-5741 



0-1922 





0-5750 



0-1925 



The magnesium oxide obtained by direct ignition of the 

 nitrate weighed on the average about 0*0010 grm. more than 

 the oxide theoretically present in the weighed sulphate from 

 equal portions of the solution. 



Before proceeding to study possible chemical effects of 

 ammonium chloride in determining the constitution of the 

 ammonium magnesium phosphate, it is obviously necessary to 

 define the extent to which the ammonium salt may exert a 

 solvent action in presence of the precipitant. Fresenius esti- 

 mated that ammonium magnesium phosphate is soluble in 

 15293 parts of cold water, but the method of investigation 

 employed did not entirely preclude the possibility of counting 

 as ammonium magnesium phosphate soluble material included 

 and held in the original precipitate. f According to Kissel;}: 

 the phosphate, which dissolves in a mixture of ammonia and 

 water in the proportion of 0*0040 grams to the liter and in the 

 proportion of 0*0110 grams to the liter in a similar mixture 



* Am. Chem. Jour., xvi, 567. 



f Fresenius, 6 te Aufl., p. 805. % Zeitschr. fur Analyt. Chemie, viii, 173. 





