14 



after adding two or three drops of rosolic acid solution (made by dissolving 

 one gramme of rosolic acid crystals in 100 c.c. of 96 per cent, alcohol), 

 .ammonia is added, very cautiously, by means of a dropping tube, until a 

 permanent pinkish colour is produced in the supernatant liquid. The 

 mixture is then boiled until the pink colour almost disappears again, the 

 .alumina and oxide of iron being thus precipitated. After cooling, the 

 flask is filled up to the mark, thoroughly shaken, and the contents filtered 

 into a 300 c.c. bottle. 100 c.c. of this clear filtrate (equal to 10 grammes 

 -of fine earth) are removed by a pipette into a 300 c.c. Erlenmeyer flask ; 

 three to five drops of acetic acid are added, which should render the mix- 

 ture feebly acid; the liquid is then heated to near boiling, and treated 

 with 20 c.c. of a four per cent, ammonium oxalate solution. The mix- 

 ture is placed on a water oven for six hours, and the precipitate is then 

 collected, ignited, weighed, and the lime calculated as CaO. 



Determination of Potash. Other 50 c.c. of the filtered soil extract 

 -(equivalent to 25 grammes of fine earth) are placed in a 300 c.c. Erlen- 

 meyer flask and boiled. 5 c.c. of a ten per cent. Barium chloride solution 

 .are added, and the mixture is boiled for another five minutes for the 

 precipitation of sulphates as Barium sulphate. After filtering into a 

 marked 250 c.c. flask, a few drops of rosolic acid are added, and boiling 

 with ammonia is proceeded with as in the case of the lime determination. 

 When partly cooled down, two or three grammes of crystalline ammonium 

 carbonate are thrown in, and the temperature is once more raised to the 

 boiling point, in order to separate calcium and barium. After complete 

 precipitation of these, the liquid is cooled, the flask filled up to the mark 

 with distilled water, and the contents filtered. Of this filtrate 100 c.c. 

 equivalent to 10 grammes* of fine earth) are placed in a platinum basin, and 

 evaporated to dryness on a water bath. The dish containing the residue is 

 heated, at first on asbestos sheet, and then carefully over a small open flame, 

 until all ammonium salts have been expelled. By means of boiling water 

 the residue is then washed through a filter into a glass dish : 2 c.c. of a 

 10 per cent, solution of platinic chloride are added, and the mixture is 

 ^evaporated to dryness on the water bath. After cooling, some dilute 

 alcohol (81 to 82 per cent.) is added to the residue, and it is allowed to 

 stand for at least half an hour. It is now filtered through a Gooch 

 -crucible by the aid of a filter pump, washed, at first, with 96 per cent., 

 and then with absolute alcohol, and dried for two hours in a water oven. 

 The weight of the crucible containing the Potassium platino-chloride hav- 

 ing been taken, the precipitate is washed through the filter with boiling 

 water, and the crucible, after again washing with alcohol, is dried and 

 -weighed. The difference between the two weighings, multiplied by *193, 

 gives the quantity of potash (K 2 0) in the ten grammes of fine earth taken. 



Determination of Phosphoric oxide. 25 grammes of fine earth are 

 placed in a marked 500 c.c. flask, 25 c.c. of concentrated nitric acid are 

 added, and the mixture is thoroughly shaken. 50 c.c. of concentrated 

 sulphuric acid are next added, and the mixture is again carefully shaken 

 up. It is then gently heated, shaking at frequent intervals. If this does 

 r.ot lead to complete oxidation, more nitric acid is added, and the heating 

 continued. Finally the mixture is cooled, and diluted to the mark with 

 distilled water; it is then well shaken and filtered. 200 c.c. of the 

 filtrate (equivalent to ten grammes of fine earth) are placed in an Erlen- 

 meyer flask of suitable size, and very nearly neutralised with strong 

 ammonia solution, a few drops of nitric acid being used to acidify the 

 mixture in case the limit is overstepped. 200 c.c. of Molybdio solution 

 prepared by dissolving 150 grammes of ammonium molybdate in a litre 



* In the citric acid extraction process (see post) this quantity will be equivalent to 20 

 grammes of the soil taken. 



