132 BULLETIN 1059, U. S. DEPARTMENT OF AGRICULTURE. 



should be added one or two drops of potassium chromate (K 2 Cr 2 4 ) 

 solution and titrated from a dropper by a weak solution of silver 

 nitrate (AgN0 3 ). If chlorine is present it will be precipitated as 

 silver chloride. The test for chlorine can be made also more simply 

 by taking some of the soil solution in a test tube and adding silver 

 nitrate solution. 



For tests of the presence of other chemical substances which 

 may be of importance in the life of plants, the following procedure 

 is suggested : 



Three hundred cubic centimeters of the soil solution are poured 

 into a porcelain dish and slowly evaporated, the drying being con- 

 tinued almost to red heat in order to burn any organic matter. If 

 the organic matter is not burned up in the porcelain dish contain- 

 ing the dry residue, aqua regia is added and the liquid evaporated 

 to dryness at least twice. The residue is then heated to red heat in 

 order to render the silicic acid insoluble. The soluble residue is 

 dissolved by heating in a weak solution of hydrochloric acid, and 

 the liquid is filtered off from the white amorphous residue of the 

 acid. The filtrate is collected into a graduate and water is added 

 to bring it up to 300 cubic centimeters. Of this the following 

 amounts are taken for further tests : 



1. One hundred cubic centimeters for determining the entire 

 amount of Fe 2 3 (ferric oxide) -\-F 2 5 (phosphorus pentoxide) + 

 A1 2 3 (aluminum oxide) -f-CaO (calcium oxide) +MgO (magnesium 

 oxide). 



The solution is neutralized with sodium carbonate (Na 2 C0 3 ) 

 until some cloudiness appears, then from 5 to 10 cubic centimeters 

 of sodium acetate (NaC 2 H 3 2 ) are added and the solution is heated; 

 the entire amount of ferric oxide and aluminum oxide will be pre- 

 cipitated in the form of basic acetates. These are filtered off. The 

 filtrate is heated and neutralized with ammonia (NH 3 ) until an 

 alkaline reaction is obtained, then 1 or 2 cubic centimeters of am- 

 monium chloride (NH 4 C1) and ammonium oxalate (NH 4 ) 2 (C00) 2 

 are added. The calcium is precipitated and is filtered off. 



To the filtrate, after it has been cooled off, are added several 

 cubic centimeters of sodium ammonium phosphte (NH 4 NaHP0 3 ), 

 and it is left to stand for several hours. If magnesium is present 

 it will be precipitated. 



2. One hundred cubic centimeters for determining S0 3 (sulphur 

 trioxide). 



For this determination the 100 cubic centimeters are heated and 

 to the solution are added several drops of barium chloride (BaCl 2 ). 

 If S0 3 is present, it should precipitate in the form of barium sul- 

 phate (BaSOJ. If it is not precipitated at once, the solution to 



