142 Analysis and Valuation of Manures [229, 230 



contains the soluble phosphoric acid, together with a certain 

 amount of H 2 S0 4 and CaS0 4 . 



The only thing to be estimated is the P 2 5 . The liquid is 

 treated exactly as the solution of mineral phosphate (paragraphs 

 198 and 199), rejecting the lime precipitate and weighing the 

 Mg 2 P 2 7 . Only 1 gram of ammonium oxalate and 25 c.c. of 

 MgCl 2 mixture must be used. 



229. Treatment of the Insoluble Portion.— The 

 filter paper containing the insoluble part of the manure is 

 transferred without drying to a platinum dish, and heated over 

 an Argand, very slightly at first, but as soon as the substance is 

 dry at the highest temperature obtainable. When the paper is 

 quite burned, the dish is allowed to cool and the substance 

 washed out with dilute HC1 into a beaker of the same size as 

 that which was used for washing out the soluble portion. 

 Twenty c.c. of strong HO are added, and allowed to digest for 

 five minutes on the water bath. Fifty c.c. of water are added 

 to complete the solution of any CaS0 4 which may be left. 

 This will take about a quarter of an hour. Finally, the sand is 

 filtered off, washed, and treated as described in the case of 

 mineral phosphates (paragraph 197). The filtrate is raised to 

 a boil, and ammonia added in excess. This precipitates 

 all the P 2 5 left by the water, in combination with iron, 

 aluminium, and lime. It is filtered off, dried, ignited, and 

 weighed. 



230. Calculation. — From the amount of Mg 2 P 2 7 

 the P 2 5 is calculated, and the correction of -33 per cent, 

 made (see paragraph 200). The percentage thus found is 

 multiplied by 99 and divided by 71 to give the percentage 

 of soluble phosphate, CaP 2 6 (the anhydrous form of 

 CaH 4 P 2 8 ). 



For purposes of valuation, the P 2 O r) is also calculated into 



