638 



SCIENCE 



[N. S. Vol. XLVII. No. 1226 



edge at what may be a new angle to some one 

 else who may thereby perceive a generalization 

 or means to discover one. This, which seems 

 to be the purpose of discussion, will be served 

 as well even though I may have fallen into 

 errors far more grievous than the apparent one 

 that has occasioned this communication. 

 Horatio Hughes 



the true soil solution 

 Just recently. Dr. C. B. Lipman has pub- 

 lishedi a preliminary paper describing a " new 

 method of extracting the soil solution," by 

 subjecting the soil to a maximum direct pres- 

 sure of 53,000 pounds to the square inch. 

 This preliminary article describes briefly the 

 apparatus used in obtaining this enormous 

 pressure and claims for this new method the 

 "obtaining of the soil solution as it exists^ in 

 relatively thin films aroimd the soil particles. 

 The procedure is rapid, clean and of high 

 efEieiency. With further improvements in ap- 

 paratus which we now are planning, the 

 m.ethod should supplant all other methods 

 known to-day, including even the Morgan 

 procedure." The fault found with the Morgan 

 method is that it is "laborious and slow, and 

 introduces the factor of oil which complicates 

 and renders it extremely time-consuming and 

 untidy." 



Let us look at the important points Dr. 

 Lipman claims for his direct-pressure method. 



It allows of the direct determination of the con- 

 centration of the soil solution, and of the amounts 

 of each of the solutes contained therein. 



The physical chemist is familiar with the 

 fact that pressiu'e is a considerable factor in 

 influencing solubilities and it does not seem 

 logical that a method employing such enor- 

 mous pressures could obtain the sail solution 

 " as it exists " in the soil without upsetting 

 the whole physico-chemical equilibrium of the 

 real soil solution; its specific gravity, vis- 

 cosity, surface tension, osmotic pressure, spe- 



1 Lipman, C. B., "A New Method of Extracting 

 the Soil Solution," TJniv. of Calif. Publ. in Agr. 

 Sciences, Vol. 3, No. 7, pp. 131-134, March 15, 

 1918. 



2 Italics ours. 



cific conductivity and its chemical composi- 

 tion would all suffer more or less of a change 

 which would combine to render the solution 

 worthless to the plant physiologist or to the 

 plant physiological pathologist from a scien- 

 tific point of view. The reason that the soil 

 solutions obtained by other methods are at 

 fault is largely because the water added in 

 extracting the soil changes the solubilities of 

 certain of the ingredients. The van Suchtelen- 

 Itano paraflin-oil displacement-pressure method 

 described by Morgan^ was worked out care- 

 fully with just the opposite idea in mind, i. e., 

 to subject the soil to as little pressure as pos- 

 sihle so as to preserve intact the physico-chem- 

 ical equilibrium of the solution obtained. To 

 this end the most inert oil was carefuUy 

 selected as the displacement medium and pres- 

 sures not exceeding 500 pounds per square 

 inch were employed for forcing the oil into the 

 soil. The preliminary tests^ of the paraffin- 

 oil displacement-pressure method, run by van 

 Suchtelen and Itano before extensive work 

 was done by these investigators and by Morgan, 

 show that the inactive paraffin oil when 

 brought into intimate contact with the soil 

 solution did not change the electrical con- 

 ductivity, chemical composition nor surface 

 tension. The solution is literally pushed out 

 of the soil by the inert oil, only sufficient 

 pressure being used to force the viscous oil 

 into the soil. 



The oil-pressure method is somewhat time- 

 consuming, laborious and untidy, but common 

 workmen after being carefully instructed can 

 do this work under the supervision of the 

 trained scientists ; again, not one but a battery 

 of as many cylinders as desired can be used to 

 obtain sufficient quantities of solution in a 

 minimum time. However if Dr. Lipman's 

 above contentions did hold true in every re- 

 spect the end in view, i. e., the obtaining of a 

 solution representing Tnost nearly in all re- 



3 Morgan, J. ¥., ' ' The Soil Solution Obtained by 

 the Oil Pressure Method," Soil Science, Vol. II., 

 No. 6, 1917, pp. 531-545, PI. 1. 



* Report of the Bacteriologist, 26th Annual Ee- 

 port of the Michigan State Board of Agriculture, 

 pp. 152-153. 



