BOX EXPERIIMENTS WITH PHOSPHORIC ACID. 67 



beginning- of the first experiment this phosphate had the follow- 

 ing composition : 20.60 per cent total phosphoric acid, of which 

 16.90 per cent was available (14.97 per cent soluble, 1.93 per 

 cent citrate soluble). In the later work it was found that the 

 composition had changed somewhat, but the amount of avail- 

 able phosphate remained about the same. 



2. Crude, finely ground Florida rock (floats), containing 

 32.88 per cent total phosphoric acid, none of which was soluble, 

 with only 2.46 per cent soluble in ammonium citrate. This was 

 obtained from the commercial ground rock by stirring it with 

 water, allowing the coarse particles to subside and then pouring 

 off the turbid water. The "floats" used in this experiment con- 

 sisted of the sediment deposited from these washings. 



3. A phosphate of iron and alumina (Redonda). The first 

 sample used contained 49.58 per cent phosphoric acid, a large 

 part of which, 42.77 per cent, was soluble in ammonium citrate. 

 The Redonda underwent such rapid changes in the intervals 

 between the experiments that it became necessary to prepare 

 fresh quantities at each successive planting. The analysis given 

 above is fairly representative of all. 



Twenty grams of the floats, containing 6.58 grams total phos- 

 phoric acid, were used for a single box. The other phosphates 

 used were first analyzed and such quantities used for each box 

 that the total quantity present was in each case the same, 6.58 

 grams. The actual amounts of available phosphoric acid thus 

 supplied to each box by the various phosphates were : by the 

 acid rock, 5.39 grams ; by the floats, .49 grams ; by the Redonda, 

 5.67 grams. 



DETAILS OF THE EXPERIMENT. 



The experiments were conducted in one of the green houses, 

 the plants being grown in wooden boxes, fourteen inches square 

 and twelve inches deep. When filled to within one and one-half 

 inches of the top, these boxes contained 120 pounds of sand. 

 The sand used was taken from a knoll near the river at a depth 

 of three or four feet, and was nearly free from organic matter. 

 Traces of phosphoric acid were present, but as this was in the 

 insoluble form and the quantity in each box was the same, its 

 presence is not considered objectionable. The sand was care- 



5 



