180 THE ANALYSIS OF MANURES. VIII. 



In the case of basic slag the tetracalcium phosphate is 

 soluble in citrate solution, but as there is always more or less 

 free lime present, Wagner recommends that sufficient citric 

 acid be added to neutralise the free lime in 5 grammes of the 

 slag, and then 200 c.c. of acid ammonium citrate (made by 

 dissolving 160 grammes of citric acid in water, adding 27'93 

 grammes of real NH 3 and diluting to 1 litre). After filtering, 

 the phosphorus pentoxide in solution is estimated by separa- 

 tion with ammonium molybdate solution and precipitation by 

 magnesia mixture as usual. 



Potassium in presence of sulphuric acid, iron, lime, and 

 magnesia. Usually the above bases and the sulphuric acid 

 have first to be removed by means of ammonia, ammonium 

 carbonate or oxalate, and barium chloride, necessitating the 

 subsequent removal of the ammonium compounds and excess 

 of barium. By direct addition of platinum chloride to the 

 hydrochloric acid solution of the original substance, evapora- 

 tion to dryness, and washing, first with a little platinum 

 chloride solution, then with alcohol, next with a 20% solution 

 of ammonium chloride, to which sufficient solid K 2 PtCl fi has 

 been added to saturate it, and lastly again with alcohol, a 

 pure double chloride of potassium and platinum may be 

 obtained. 



THE VALUATION OF MANURES FROM ANALYSIS. 



From the percentage amounts of the valuable constituents in 

 a manure and its commercial value per ton, it is easy to calcu- 

 late the cost of the actual valuable ingredient per H)., or, as is 

 perhaps more usual in this country, " per unit," i.e., the value 

 per ton of each per cent. 



For example, take nitrate of soda, containing, say, 15'75% 

 nitrogen, and assume its price per ton to be 8. 

 Nitrogen in this form costs 

 8 x 20 x 100 

 2240x15-75 =: 



or its value " per unit" = . = ]0'2s. 10s. 2 



