112 



the (jiiestion of tlie relative (jiiantities of the soil and solvents used as the present 

 amcunts — 200 grams soil to 1 liter of solvent — seems to involve too small a vol- 

 ume of solvent. While we feel encouraged by the outcome of the work reported 

 above, it must be borne in mind that before any method of soil testing can be con- 

 sidered satisfactory, it must give reliable indications on soils of different types 

 that have been subjected to investigation by field tests ; and these tests must not 

 be confined to one crop, but must relate to all the crops likely to be produced on 

 the land under investigation. From data now at hand it seems probable that 

 certain soils may have ample potash in an available form to produce good crops 

 of cereals, while not having enough to produce profitable crops of corn, potatoes, 

 or tobacco. This phase of the matter must be kept in mind in deciding upon any 

 definite amount of soluble ingredients which shall be used as a minimum in judg- 

 ing of th-" fertilizer needs of a soil. 



Purdue Agricultural Experiment Station, November, 1896. 



(1) Jour. Chem. Soc, London, March, 1894. This paper contains a resume of 



suggestions by various authors and special investigations by Dr. Dyer. 



(2) Chem. Div. U. S. Dept. Agr., Bull. 47, p. 32. 



(8) Rhode Island Agr. Exp. Sta., 7th Ann. Rpt., p. 152. 



(4) Chem. Div. U. S. Dept. Agr., Bull. 38, p. 84; Wiley's Agr. Analysis, vol. 1, 



p. 32(5. 



(5) Chem. Div. U. S. Dept. Agr., Bull. 31, p. 99. 



(6) Determined by Harry Sn3'der. See Bull. 47, l^. S. Dept. Agr., Chem. Div., 



p. 49. 



Action <>i' Ammonium Citrate and Citric Acid on Basic Slag. By H. 

 A. Huston and W. J. Jones, Jr. 



[Abstract.] 



This is a continuation of the work carried on for several years by the authors 

 under the general head of the availability of commercial phosphates. This paper 

 deals with the two most prominent materials proposed for determining the avail- 

 ability of the phosphoric acid in the slag. The factors controlling the action of 

 the reagents are discussed under the following heads: 

 I. Influence of time of digestion. 

 II. Influence of temperature. 



III. Influence of acid (citric) ar.d alkali (ammonia). 



IV. Influence of quantity of slag used. 



