§ 104. MISCELLANEOUS ESTIMATIONS. 185 



in the form of humus, that is extracted from the soil by- 

 water or alkaline solutions, the following method is given 

 by Schulze. Boil 10 grms. of soil 15 minutes with 200 

 c.c. of a solution containing 0.5" |„ of potassa, bring the 

 volume of the whole to 250 c.c, pour the liquid on a dry- 

 filter, or through dry, fine-grained sand with which the 

 throat of the funnel is stopped ; put 4-6 c.c. of the filtrate 

 in a flask^f about 200 c.c. capacity, dilute with about 100 

 c.c. of water, and determine organic matter in 100 c.c. of 

 this solution by means of standard solutions of potassic 

 permanganate and oxalic acid (§ 91, e). 



h. Ammonia* — The amount of ammonia existing al- 

 ready formed in soils is nearly always very small, since it 

 is so readily converted into nitrates. 



To determine it by Schlossing's method (§ 47, ^), treat 

 50 grms. of soil with 40 c.c. of a cold saturated solution 

 of sodic hydrate. After 48 hours remove the acid from 

 under the bell-jar, titrate it, stir the soil in the watch- 

 glass, put another measured portion of acid in the proper 

 vessel, and, after 48 hours, titrate this also with the 

 standard sodic solution. If no more ammonia was set 

 free during the second period, the first determination 

 may be considered, sufiicient; if more was set free, it 

 should be added to the first quantity found, and a new 

 portion of acid should be put in, in the place of the last, 

 and tested after 48 hours. 



It may also be desirable to estimate the ammonia that 

 is set free on heating the soil with magnesia. Pour 500 

 c.c. of water containing 5 grms. of freshly ignited mag- 

 nesia over 100 grms. of soil, mix the whole well together, 

 and proceed to distil off the ammonia (§ 47, c). 



Probably no great reliance can be placed on any method 

 of determining ammonia in soils. 



c. Nitric acid. — The accurate determination of nitric 

 acid is not difficult, as the nitrates are so easily extracted 

 from the soil by water. 



