11] 



SOILS 



19 



residual gas to the graduated burette (B), and again read the burette noting the 

 temperature and pressure. The difference in readings calculated to standard con- 

 ditions of temperature and pressure gives the number of cc. of carbon dioxid derived 

 from the total carbon in the sample. Conduct a blank determination upon the 

 reagents used. If an appreciable amount of carbon dio.xid is obtained in the blank, 

 the result expressed in terms of total carbon must be corrected accordingly. 



Determine the inorganic carbon as directed under 9 and subtract it from the total 

 carbon to obtain the organic carbon. 



INORGANIC CARBON. 

 Modified Marr Methods — Tentative. 



7 REAGENTS. 



(a) N/IO hydrochloric acid. 



(b) N/10 sodium hydroxid. 



(C) Dilute hydrochloric acid. — Dilute 25 cc. of concentrated hydrochloric acid 

 (sp. gr. 1.19) to 250 cc. with carbon dioxid-free water. 



(d) Barium hydroxid solution. — Prepare a saturated aqueous solution of barium 

 hydroxid, filter through asbestos into a large container through which air free 

 from carbon dioxid has been aspirated for some time, and provide an arrangement 

 whereby the solution may be delivered by air pressure or gravity and kept from 

 contact with carbon dioxid by means of soda lime tubes. 



(e) Carbon dioxid-free water. — Use recently boiled and cooled water, or water 

 from which carbon dioxid has been removed by aeration for a sufficient length of 

 time with carbon dioxid-free air. Keep in a container provided with a similar 

 attachment as in (d). 



8 



APPARATUS. 



HALF FULL OF 



BEADS OR . 



BROKEN GLASS 



'iri 



■Lfl 



FIG. 3. MODIFIED MARR APPAR^VTUS FOR DETERMINING CARBON DIOXID. 



The apparatus required (Fig. 3), consists of a tube {A), 50-60 cm. long, partly 

 filled with beads or broken glass and containing strong potassium hydroxid solution 

 (1 to 2), a cylindrical open top separatory funnel {B), capacity 50 cc, marked at 20 and 

 40 cc, the stem of which extends almost to the bottom of the 250 cc. fiask (C) into the 



