SOILS. 19 



mometer in the flask, and heat to exactly 85 C. Add 75 cc of recently pre- 

 pared molybdate solution, digest in a water bath at 80 C. for 15 minutes, 

 with occasional shaking, remove from the bath and allow to stand at least 10 

 minutes before filtering. Continue the determination in the usual way. 



9. Lithium, Caesium, and Kubidium. Official. 



The salts of these elements are occasionally found in very small amounts in 

 soils. Their agricultural uses are still in question, and their amount is too 

 small to admit of quantitative estimation. A qualitative examination may be 

 made by the spectroscope with the water-soluble materials evaporated to dry- 

 ness and dissolved with two or three drops of hydrochloric acid or with the 

 alkaline chlorids separated as in 5 (h), page 17, or " 7. Total Alkalies," page 18. 



10. Total Nitrogen. Official. 



Place from 7 to 14 grams of the soil in a Kjeldahl digesting flask, with 30 cc 

 of strong sulphuric acid, or more if necessary, and 0.7 gram of mercuric oxid 

 (or its equivalent in metallic mercury), and boil for several hours. Oxidize the 

 residue with potassium permanganate in the usual way. After cooling half 

 fill the flask with water, shake it vigorously, allow the heavy matters to sub- 

 side, and pour the supernatant liquid into a flask of about 1,000 cc capacity. 

 Repeat this operation until the ammonium sulphate is practically all removed 

 and the distillation flask is a little more than half full; distil the ammonia in 

 the usual manner. If the sample be known to contain a considerable amount of 

 nitrate, use method "4. (c)," page 7, under analysis of fertilizers. 



11. Carbon Dioxid. Official. 



Determine as under analysis of inorganic plant constituents, "2. (c)," page 

 21, using from 5 to 10 grams of the sample. 



12. Humus. Official. 



Place 10 grams of the sample in a gooch crucible, extract with 1 per cent 

 hydrochloric acid until the filtrate gives no precipitate with ammonium hydroxid 

 and ammonium oxalate, and remove the acid by washing with water. Wash the 

 contents of the crucible (including the asbestos filter) into a glass-stoppered 

 cylinder, with 500 cc of 4 per cent ammonium hydroxid, and allow to remain, 

 with occasional shaking, for 24 hours. During this time the cylinder is 

 inclined as much as possible without bringing the contents in contact with 

 the stopper, thus allowing the soil to settle on the side of the cylinder and 

 exposing a very large surface to the action of the ammonium hydroxid. Place 

 the cylinder in a vertical position and leave for 12 hours, to allow the 

 sediment to settle. Filter the supernatant liquid (the filtrate must be per- 

 fectly clear), evaporate an aliquot, dry at 100 C., and weigh. Then ignite the 

 residue and again weigh. Calculate the humus from the difference in weights 

 between the dried and ignited residues. 



13. Humus Nitrogen. Official. 



Digest the soil with 2 per cent hydrochloric acid and wash as nearly free of 

 acid as possible with distilled water. Extract the humus with a 3 per cent 

 solution of sodium hydroxid and determine nitrogen in the extract in the usual 

 way. 



