168 THOMAS COOKSEY. 



Examples — 

 Fe 2 3 found by iodine thio-sulphate 

 P 2 O s in filtrate 



Total P 2 5 added to solution 



P 2 5 in filtrate 



P 2 5 combined with Fe 2 3 and A1 2 3 ... '0960 '0953 

 Calculated P a Oy combined with Pe 2 3 found 



above *0342 *0340 



I. 



II. 



•0386 



•0384 



•1406 



•1413 



•2366 



•2366 



•1406 



•1413 



P,0 5 combined with A1 2 3 '0618 *0613 



A1 2 3 calculated from last figures ... *0446 '0443 



AloOs in solution (mean of 5 determ. as A1 2 3 ) '0445 

 Estimation of iron and alumina by weighing as phos- 

 phates.— Both iron and alumina can be accurately estimated 

 by precipitating the phosphates of these metals in the 

 manner previously described and given more in detail later. 

 The method is more especially useful in the estimation of 

 alumina when occurring with phosphoric acid. 



Estimation of Iron. 

 Example — 



a. Fe a (P0 4 ) a '0766 equivalent to 



b. Fe 3 (P0 4 )a '0761 equivalent to 



Fe 2 3 found by iodine and thio-sulphate 

 Fe 2 3 by weighing as such 



Estimation of Alumina. 

 Example — A1 2 (P0 4 ) 2 '1620 equivalent to 

 AI0O3 by weighing as such ... 



The estimation of iron, aluminium, and phosphoric acid 

 when present together in solution.— The estimation of these 

 three substances when occurring together has always been 

 a somewhat lengthy operation and is usually carried out 

 by the preliminary precipitation of the phosphoric acid by 

 means of ammonic-uitro-molybdate. Other methods are 

 available, but in any case the processes are tedious and a 



•0407 Fe 



2 3 



•0403 Fe 



2 3 



•0404 Fe 



2 o 3 



•0408 





•0678 A1 2 3 



•0680 





