210 EXPERIMENT STATION EECOED. 



to consider (1) The recognition of the problem at hand in deciding on the methods 

 for its solntion ; (2) the methods utilized for sampling the soil in the field; 

 (3) the size of the soil particles in the sample to be examined; (4) the quality 

 and quantity of the solvent employed; and (5) other factors which affect the 

 solution, such as temperature, time of exposure to solvent, concentration, etc. 

 The various points are further analyzed and discussed. 



Preparation of the soil extract for chemical analysis, A. Vesterbeeg (/J. 

 Conf. Agrog^ol. Internat. Stockholm, 1910, R^sum^ [1], pp. 3^, 35). — The 

 author points out that in order to judge the characteristics of the soil properly, 

 particularly its content of plant nutrients and products of weathering, it is 

 necessary to utilize a comparatively stroug solvent. Other factors to be con- 

 sidered in this connection are the nature and amount of solvent, the tempera- 

 ture, and the time of exposure to the solvent. 



The author recommends the following procedure for mineral soils: Extract 

 1 part of soil with 5 parts of a hydrochloric acid solution (six times normal) 

 boil for a period of 1 hour, and determine in the resulting extract K2O, PzOb 

 and (Fe Al)203. The amount of (Fe Al)j03 found in the extract is a measure 

 as to the amount of the weathering-silicates (zeolithic) contained in the soil. 

 For the sake of completeness the author also recommends determining the 

 soluble silicic acid itresent in the residue after extracting with hydrochloric 

 acid solution. The calcium content can be calculated from the results of the 

 carbon dioxid determination, or it can be extracted with a cold 2 per cent 

 solution of acetic acid (or a warm ammonium chlorid solution) and the amount 

 of calcium determined directly. 



The electrical bridge for the determination of soluble salts in soils, 

 R. O. E. Davis and H. Bryan (U. S. Dept. Agr.. Bur. Soils Bui. 61, pp. 36, 

 pis. 5, figs. 7). — This is a discussion of the principles of the slide wire bridge 

 as used by the Bureau of Soils of this Department, with a detailed description 

 of a modification of the apparatus, previously described (E. S. R., 11, p. 32.5; 

 12, p. 320). The bulletin also includes some experimental results obtained with 

 the instrument, and which Lave particularly to do with determining the causes 

 for certain differences in the results obtained with the method. 



The conclusions from this work were as follows : " The resistance of a soil 

 having the same salt content increases with an increase in the fineness of 

 texture of the soil. Where the salt is partly carbonates the resistance is much 

 greater than when other salts alone are present. The presence of organic 

 matter increases the resistance for~the same salt content. If a soil is dry, the 

 reading for resistance should not be made until 20 minutes have elapsed after 

 moistening. Accurate enough results may be obtained with concentrated solu- 

 tions by reading resistances with the cup partly filled." 



The authors point out that when considering these conclusions for field work 

 it must be noted that the method only reaches its full accuracy when the 

 alkalis contain very little or no carbonate and when the amount of organic 

 matter is small. For eliminating the error caused by carbonates, the authors 

 have constructed special tables giving ratios for various combinations of car- 

 bonates and other alkalis as determined in the area under investigation, though 

 in areas whei'e much variation exists the bridge results must be considered only 

 as approximate. The method is not recommended for soils which contain much 

 organic matter owing to the difficulty of preparing standards for such soils. 



The bulletin also describes field directions for the use of the bridge. 



Volumetric determination of copper, E. B. Holland (Massachusetts Sta. 

 Rpt. 1909, pt. 1, pp. l-'/O, HI). — This method is an adaptation of the Low zinc- 

 acetate method and has been employed by the author for estimating the copper 

 in the cuprous oxid obtained in the AHihn tubes in sugar estimations. Its chief 



