281-284] Determinations in Separate Portions of Soil 167 



pump going and allow the water to run through. Now add 

 another 50 c.c, and allow the pump to continue working until 

 water ceases to drop into b. The liquid is then ready for 

 further treatment. 



281. Nitrates. — Pour the extract obtained as described 

 in the last paragraph into a platinum dish. Wash the flask 

 twice, and add the washings to the rest of the liquid. Evapo- 

 rate over the water bath until only about 5 c.c. is left. Wash 

 this liquid with a little hot water into Schloesing's nitrate 

 apparatus (fig. 31), and determine the nitrogen exactly as 

 described in paragraph 107. 



282. Chlorine. — Extract another portion of the soil in 

 exactly the same manner, and estimate the chlorine with stan- 

 dard AgN0 3 solution as described in paragraph 69. 



283. Carbonates. — Estimate the C0 2 by one of the 

 methods described in paragraphs 48-53. The quantity of soil 

 to be used in this operation varies according to the nature of 

 the soil. About 5 grams will generally be found convenient, 

 but should large quantities of lime or magnesia be found in the 

 earlier part of the analysis, a smaller quantity of the soil will 

 be required. On the other hand, soils very poor in lime and 

 magnesia are correspondingly poor in carbonic acid. 



284. Organic Carbon. — The organic portion of a soil 

 generally goes by the name of 'humus,' and this humus is 

 usually found to contain 58 per cent, of carbon. If, therefore, 

 we estimate the carbon, we are able to calculate the quantity of 

 humus ; and seeing that we have in a previous part of the 

 analysis estimated the loss on burning, we can calculate, by 

 difference, the percentage of combined water in the soil. The 

 determination of carbon is conducted as follows : Fit up an 

 apparatus similar to the one described in paragraph 55 and 

 shown in fig. 22, the only difference to be made being the 

 omission of the pipette d, for which is substituted an ordinary 



