PRACTICE XXXV 



EFFECT OF SOLUBLE SALTS ON RETENTION OF 

 CAPILLARY WATER 



Use the stock soils, loose and compact, in the same tubes as 

 in Practices XX, XXI, and XXII. 



Make separate determinations for each solution, but run loose 

 and compact soil at the same time. 



Use distilled water and the following solutions: one-half 

 normal ^ sodium chloride (NaCl), normal and three times normal 

 solutions, and one-half normal and three times normal solutions 

 of the following mixture of salts : sodium chloride (NaCl), sodium 

 carbonate (Na2C03), sodium nitrate (NaNOg), sodium sulfate 

 (NagSO^), potassium nitrate (KNO3), and potassium chloride 

 (KCl). If desirable other salts may be added or substituted 

 for any of these. 



Determine the percentage of water retained and the acre 

 inches, as in the preceding practices. 



Explain your results. 



References. 



'^Physical Properties of Soil/' Warington, pp. 211-231. 

 " Principles and Practice of Agricultural Analysis," Wiley, Vol. I^ 

 p. 170. 



1 By a normal solution is understood one which contains one " gram-equivalent '* 

 of the active reagent dissolved in one liter of solution. By "gram-equivalent" is 

 meant the amount of substance corresponding to one gram-atom (1.01 g.) of hj^dro- 

 gen ("Analytical Chemistry," Treadwell and Hall, Vol. II, p. 423). A normal solu- 

 tion of sodium chloride then is one in which one liter of solution contains the 

 number of grams of NaCl represented by its molecular weight, or 58.5 g. of 

 NaCl (Na = 23.05 4- CI = 35.45). 



A twice normal solution contains twice as much NaCl, or 117.0 g. per liter of 

 solution. 



A normal solution of sodium carbonate (NagCOs) contains the number of grams 

 per liter of solution represented by one half of the molecular weight, as there are two 

 hydrogen equivalents in the molecule of Na2C03. 



NagCOg (Nas = 46.1 + C = 12 + O3 = 48) = 106.1 ; then 53.05 g. of NagCOg per liter 

 is a normal solution. 



A one-half normal solution of NaCl is equivalent to 29,250 parts per million, or 

 2.925 per cent of the solution is NaCl; a normal solution of NaCl, 58,500 parts per 

 million, or 5.85 per cent. A one-half normal solution of Na2C03 is equivalent to 26,525 

 parts per million, or 2.65 per cent; a normal solution of Na2C03, 53,050 parts per 

 million, or 5.305 per cent. 



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