115 



a ...operator in the past, the referee thought it best not. to ask for too much work, and 

 in accordance with this view only one other line of investigation was requested of 

 those who expressed a willingness to cooperate. In the opinion of the referee, the 

 sodium peroxid fusion method for total phosphorus had some very serious disad- 

 vantages, particularly as to manipulation and length of time required for the determi- 

 nation. It was thought desirable to ask that a method in use in this laboratory be 

 tested with a view to proposing it as a provisional method for total phosphorus in 

 soils. 



This method, which may be known as the magnesium nitrate method, is easy of 

 manipulation and rapid, and in this laboratory has given uniformly as good results 

 as the sodium peroxid fusion. Accordingly, it was asked that these two methods be 

 compared. 



Two well-known Kentucky soils were selected for this work. No. 1 is a cultivated 

 soil from the western coal field. A complete analysis made by this station shows it 

 to l.e poor in pho-phaies, organic matter, and nitrogen. No. 2 is a virgin soil from 

 thr I >e\onian in the eastern part of Clark County, known by analysis, as in the case of 

 NM. 1. i" !> particularly rich in phosphates, organic matter, and potash. 



uples were prepared and sent to fourteen chemists, who volunteered to aid in 

 t hi- work, with the following instructions: 



INSTRUCTIONS. 



(a) Make a determination of moisture by the official method, reporting the per- 

 centi 



(6) \\ eiL-h lo irraiiH of sodium peroxid into an iron or porcelain crucible and thor- 

 euiirhl) mi \ \\ iih it 5 grains of the soil. If the soil is very low in organic matter, add 

 a link .-larch '" ha.-teu the action. Heat the mixture carefully by applying the 

 flame of a Hun-en burner directly upon the surface of the charge and the sides of the 

 crucible until the action start- < 'over crucible until the reaction is over, and keep 

 at a low red heat for fifteen minutes; do not allow fusion to take place. By means 

 of a large funnel and a stream of hot water transfer the charge to a 500 cc measuring 

 flask. Acidify with hydnx-hloric acid and boil. Let cool and make up to the mark. 

 If the action has taken pi. ire properly there should be no particles of undecomposed 

 soil in the bottom of the flask. Allow the silica to settle and draw off 200 cc of the 

 clear sol u i 



Precipitate the iron, alumina, and phosphorus with ammonium hydroxid; filter, 

 wash, return the precipitate to the beaker with a stream of water, holding the funnel 

 the beaker, and dissolve the precipitate in hot hydrochloric acid, pouring the 

 acid upon the filter to dissolve any precipitate remaining. Evaporate the solution 

 and to complete dryness on the water bath. Take up with dilute hydro- 



chloric acid, heating if necessary, and filter out the silica. Evaporate filtrate and 

 to about lo cc, add '2 cc of concentrated nitric acid, and just neutralize with 

 ammonium hydroxid. Clear up with nitric acid, avoiding an excess. Heat from 40 

 to 50 on water bath, add 15 cc of molybdic solution, keeping at this temperature 

 f.r from one to two hours. Let stand overnight, filter, and wash free of acid with 

 0.1 per cent solution of ammonium nitrate; finally, once or twice with cold water. 

 Iter to beaker and dissolve in standard potassium hydroxid (1 cc equal to 

 0/J mi; of phosphoru.- , titrate the excess of potassium hydroxid with standard nitric 

 acid, using phenolphthaleiu as indicator. 



(c) Weigh into a 50 cc porcelain dish 5 grams of soil. Moisten with 5 to 7 cc of 

 magnesium nitrate solution ( (g) p. 2, Bui. 107, Bureau of Chemistry). Bring to 

 dryness on water bath, burn off the organic matter at low redness; when cool, moisten 

 slightly with water, add 10 cc of concentrated hydrochloric acid, digest two hours 

 on wafer l.ath, keeping the dish covered with a watch glass; stir up two or three 

 times during digestion. 



Make up to i'50 cc, mix well and throw on a dry folded filter, pouring back on the 

 filter till the solution runs through clear. Take aliquots corresponding to 2 or 4 

 irrams <4 Drains in Xo. 1, 2 grams in No. 2), depending upon the amount of phos- 

 phorus pre-ent . Hrin.u' to dryness, take up with hydrochloric acid and water, filtering 

 over pump. Filtrate and washings should not exceed 30 or 40 cc. Make alkaline 

 with ammonia, and dissolve the precipitate with concentrated nitric acid, using a 

 slight excess. Add gradually, while shaking, 5 to 15 cc molybdate solution (p. 2, 

 Bui. 107). After standing a minute or two add 15 cc of ammonium nitrate (p. 2, 



