Jan. 21, i9i8 Relation of Carbon Dioxid to Soil Reaction 141 



a simplified form of the apparatus used by McClendon and Magoon (7) 

 and McClendon (6) for investigating the H-ion concentration of sea water, 

 we have been able to obtain the desired data. 



DESCRIPTION OF APPARATUS AND RESULTS OBTAINED 



The hydrogen-electrode apparatus was the same as that previovisly 

 described in this journal. To provide a chamber for mixing the hydrogen 

 and carbon dioxid a graduated i ,000-c. c. cylinder, the base of which had 

 been cut off, was immersed in a larger cylinder filled with mercury. The 

 upper end of the inner cylinder was tightly stoppered and contained two 

 capillary stopcocks for admission and outlet of the gases. A definite 

 quantity of purified hydrogen, electrolytically generated, was admitted to 

 this cylinder through one stopcock. Through the other stopcock there 

 was admitted from a gas burette a known quantity of pure carbon dioxid. 

 Both gases were measured at atmospheric pressure. A sufiicient time 

 „was then allowed for the thorough diffusion of the gases, which was aided 

 by raising and lowering the inner cylinder. The reservoir of mixed gases 

 was then connected to the hydrogen-electrode chamber which contained 

 the soil suspension. Forty to seventy c. c. of the gas mixture were forced 

 into the space above the soil suspension, adjusted to atmospheric pressure, 

 and the hydrogen-electrode cell was then closed. Equilibrium was 

 hastened by the shaking method, and the voltmeter readings were noted. 

 This procedure was repeated with new portions of the gas mixture until 

 the voltmeter readings were constant to within 0.005 volt. The experi- 

 mental details and results are recorded in Table I. 



The term "With previous car bona tion" signifies that carbon dioxid 

 has been passed through the soil suspension for a period of >^ to 2 hours 

 previous to the determination of the H-ion concentration. The purpose 

 of this step was to ascertain the effect of thoroughly saturating the soil 

 with carbon dioxid upon its subsequent reaction. This also proved to 

 be necessary in the case of some of the alkaline soils to insure complete 

 saturation of the carbonates present, thus making it possible to attain 

 the final equilibrium when using the smaller percentages of carbon 

 dioxid, without the preparation of excessive quantities of the gas mix- 

 ture. By satisfying in this manner the capacity of the soil to combine 

 with carbon dioxid, it is possible to reach a partial pressure of carbon 

 dioxid above the suspension in the hydrogen-electrode cell comparable 

 to that in the mixing cylinder. 



As expressed in Table I the o per cent of carbon dioxid means that 

 several portions of pure hydrogen were used to obtain equihbrium. 

 With such a technic the loss of carbon dioxid from the soil is minimized . 

 Thus, the atmosphere above the suspension will undoubtedly contain a 

 small percentage of carbon dioxid. 



