!li' 



l.liiii Riiiiiin iiK iits of Ccrtfiui Soilx 



20()-.'5()() c.c. of approximately N/5() solution of calcium bicarbonate, 

 and the air in the bottle is displaced by a current of carbon dioxide in 

 order to insure against possible precipitation of the calcium carbonate 

 during the period of the determination. The bottle is then placed in a 

 shaking machine for thr(>e liours^, after wliich time it is opened, the 

 liquid is filtered, and a portion of the filtrate equal to half the original 

 amount of bicarbonnte solution is titrated with N/H) acid using methyl 

 orange as indicator. Tiu' dilference between this final titration and 

 that of the initial solution represents the amount of calcium carbonate 

 absorbed, each cubic centimetre of N/IO acid being equal to 5 mgrms. 

 of calcium carbonate. 



Preliminary work with this method served to show that with neutral 

 soils there was practically no absorption, while the presence of carbonate 

 in a soil often resulted in an increase in the strength of the solution 

 during the period of the determination. For all our routine work a 

 small rotary shaker was used which gave a gentle agitation to the 

 contents of the bottles. 



The extent of interaction between soil and solution obviously 

 depends largely on the rate at which the soil particles are broken down, 

 and in order to ascertain the minimum time required for this action a 

 very unkind acid Oxford clay soil was used after being passed through 

 a 3 mm. sieve. The results are included in tlie following table. 



In view of the relatively high absorption after two hours and the 

 lack of increase after this period, even with this heavy soil, we felt 

 justified in taking three hours as the maximum period for further work. 



As might be anticipated the strength of the bicarbonate solution 

 regulates the amount of absorption with any given soil and it appears 

 impoitant that, for the reaction to approach completion within the 

 prescribed period, the concentration of the initial solution should not 



• Occasional sliaking by hand (at intervals of 20 minutes) for four hours, gives identical 

 results. 



