808 EXPERIMENT STATION EECOKD. 



Soil carbonates. — A new method of determination, W. H. MacIntiee and 

 L. G. Willis {Tennessee Sta. Bui. 100 {1913), 2)p. 83-97, figs. 2).— The purpose 

 of this investigation was to determine (1) the mineral acid least active upon 

 soil organic matter in the estimation of carbonates in soils, (2) the concentra- 

 tion of the acid which would be best suited to all occurrences in light or heavily 

 limed soils, and (3) whether the determination could be made with the ordinary 

 laboratory equipment without the application of heat. 



In other work the senior author has used phosphoric acid in lieu of hydro- 

 chloric acid for the estimation of soil carbonates. In the work now reported a 

 comparative study was made of sulphuric, hydrochloric, and phosphoric acids, 

 all being tested in three strengths for this purpose. The soil used was a fairly 

 fertile loam of marked acidity with a carbon dioxid content of 0.0196 per cent. 



Phosphoric acid was found the least active toward soil organic matter. Sul- 

 phuric acid was the most active in this respect. 



Accordingly the activity of a 1 : 15 solution of phosphoric acid toward the 

 organic matter contained in an orginal loam soil was compared with the 

 action on the carbonaceous material in the same soil subsequent to treatment 

 with a 1 per cent solution of hydrochloric acid and carbonated water to remove 

 any carbonates which might be present. The data show that boiling with acid 

 gives practically identical results on an acid soil both before and after elimi- 

 nation of carbonates. Boiling an untreated acid soil with carbon dioxid-free 

 distilled water also showed an evolution of carbon dioxid. " This shows 

 either action of heat upon the soil organic matter or reaction between minute 

 localized occurrences of soil acids and carbonates." 



The Marr method (E. S. R., 22, p. 511) was studied with boiling and at room 

 temperature, except that instead of sulphuric acid phosphoric acid was used on 

 a soil in which the carbonates were removed by cold digestion with 1 per cent 

 hydrochloric acid. " The results show considerably less action on organic mat- 

 ter at 50° C. than that effected by boiling, but appreciably more than at room 

 temperature. The same results were also found in the case of well-rotted barn- 

 yard manure and of barnyard soil. The addition of 48 tons per acre of manure 

 was found to cause no increase in carbon dioxid evolution by treatment with 

 one-fifteenth phosphoric acid in the cold." " Phosphoric acid 1 : 15 at room 

 temperature liberates all of the carbon dioxid from calcium carbonate and 

 magnesium carbonate in soils, and the carbon dioxid evolved can be collected 

 by aspiration with suction, either gravimetrically or volumetrically." 



"The following method . . . has given entire satisfaction, having been used 

 upon 135 soil samples which were under absolute laboratory control and cover- 

 ing light and heavy occurrences of carbon dioxid. Where evolution of carbon 

 dioxid is not greater than 0.2 gm.. 50 gm. of soil may be used, the amount of 

 soil for the charge being decreased with an increasing percentage of carbon 

 dioxid. The evolution is kept to this amount in order that the soda-lime tubes 

 may be effective for more determinations. A separatory funnel connected with 

 purifying apparatus leads through a 2-holed rubber stopper to the bottom of a 

 300 cc. Erlenmeyer flask. Through the second hole is inserted a bulb tube 

 leading to 2 purifying bottles containing concentrated sulphuric acid. To the 

 second acid bottle is attached a U tube containing soda lime and this is at- 

 tached to a tube containing pumice stone saturated with concentrated sulphuric 

 acid. ... If volumetric determinations be desired, a Folin absorption tube or 

 a tower containing glass beads may be used. After purifying the atmosphere 

 of the apparatus, 60 to 100 cc. of phosphoric acid 1 : 15, carbon dioxid-free, is 

 added through the funnel and the carbon dioxid drawn off at a very slow rate, 

 with constant agitation, for 10 minutes. The second 10 minutes the rate is 

 slightly increased, and during the third 10-minute period purified air is drawn 



