112 AGRICULTURAL ANALYSIS 



ment of the material. This means simply the study of an incom- 

 plete reaction, and one which is interrupted while the solution is 

 very rapidly going on. This, of course, is only clearly brought 

 out by comparison of long-time and short-time work in the 

 various tables. In the opinion of Huston, much more work 

 will have to be done before it can be assumed that we have any 

 very clear knowledge of this subject, and probably the conclusion 

 will be that all kinds of materials can not be examined by the 

 same method. The fact that half a gram of dicalcium phosphate 

 is instantly soluble in 100 cubic centimeters of citrate solution, 

 at ordinary temperatures, while an equal amount of iron and 

 aluminum phosphate is acted upon very slowly at ordinary tem- 

 peratures will probably have to be taken into consideration, as 

 well as the fact that dicalcium phosphate is less soluble in hot 

 solutions of ammonium citrate than it is in cold solutions, while 

 the reverse is true of the precipitated iron and aluminum phos- 

 phate. 



At present the only conclusion that can be safely drawn from 

 the work is that it would be unsafe to make any generalization 

 upon the subject until more facts are at hand, except that the 

 methods generally in use are unscientific and unsatisfactory. As 

 the work progresses, new features present themselves, and in such 

 a way as to show that they must be given careful consideration 

 before drawing any final conclusions in the matter. At best, it 

 must be confessed that the action of a neutral ammonium citrate 

 solution on the various forms of phosphates entering into the 

 composition of commercial fertilizers is a practically continuous 

 process, varying in speed with changing conditions of tempera- 

 ture, time, relation of quantity of sample to volume of substance, 

 and the fineness of subdivision of the sample. Concordant re- 

 sults can therefore only be obtained by observing fixed conditions 

 of work. 



101. Arbitrary Determination of Reverted Phosphoric Acid.. 

 The so-called reverted phosphoric acid, that is, the acid insoluble 

 in water and soluble in a solution of ammonium citrate, is the most 

 annoying constituent of commercial fertilizers from the point 

 of view of the scientific analyst. A review of all the standard 



