150 Analysis and Valuation of Manures [251, 252 



paper with strong alcohol, well washed, dried, and weighed as 

 described in paragraph 32. The NaCl is added to turn all 

 K 2 S0 4 into KC1. The preliminary washing with PtCl 4 is to 

 remove any double compounds of platinum with magnesium 

 and sodium, which would be insoluble in alcohol. 



251. Another Method. — Weigh out about -5 gram of the 

 substance. Dissolve in water. To the solution, which con- 

 tains the sand in suspension, add Ba(OH) 2 solution until 

 alkaline. Allow the precipitate to settle, keeping the beaker 

 on the water bath. Filter rapidly, and wash well with boiling 

 water. The precipitate consists of barium sulphate and mag- 

 nesia, which may be rejected. Make the solution acid with 

 HC1. Raise it to boiling-point, then add hot BaCl 2 drop by 

 drop, until ho further precipitate occurs. This is best done by 

 keeping the beaker on a water bath, and allowing the precipitate 

 to subside after each few drops. When no further precipitate 

 forms there will be a small amount of BaCl 2 in solution, 

 together with all the potassium in the state of chloride. The 

 barium must be removed by a drop or two of dilute H 2 S0 4 

 and the BaS0 4 filtered off and washed. The filtrate is evapo- 

 rated down and estimated as in paragraphs 33-35. As small 

 quantities of Mg and Na may be present, it is best to moisten 

 the pasty substance with a little PtCl 4 solution and decant 

 through the filter paper before using alcohol. 



ANALYSIS OF AMMONIUM SALTS 



252. As these salts are generally prepared as by pro- 

 ducts in coal gas manufacture, it is always possible that they 

 may contain traces of ammonium sulphocyanate, which is a 

 strong plant poison. They should therefore be tested quali- 

 tatively for NH 4 CNS with Fe 2 Cl 6 , which should give no red 

 colouration. 



