i68 THE CHEMICAL ANALYSIS OF SOILS [chap. 



is affected by so many temporary factors which pre- 

 vent the comparison of one soil with another. 



As, however, the determination of the amount of 

 nitrate present in a soil is often required for other 

 purposes, it will be convenient here to indicate the 

 method to be followed. In the first place, the soil 

 must be analysed either immediately after it has been 

 sampled or after rapid drying with the aid of heat, 

 for the manipulation a soil sample usually receives in 

 the drying, sifting, and other preliminary operations, 

 will cause the production of large quantities of nitrates 

 in soils containing moisture. 



A funnel with a large filtering surface, at least 2 

 inches in diameter, must be taken ; Warington originally 

 made use of the inverted upper portion of a Winchester 

 quart bottle with a disc of copper gauze, 2 inches in 

 diameter resting in the neck, but this may be replaced 

 advantageously by a Buchner funnel 6 inches in 

 diameter. In either case the funnel is connected with 

 an exhaust-pump, the disc is covered with a good 

 filter paper wetted, then at least 500 grams of the soil 

 are packed carefully into the funnel and pressed down a 

 little, care being taken to avoid plastering if the soil is 

 clayey. The soil sample as it comes from the field is 

 spread out, roughly crumbled, and mixed ; from this the 

 500 grams or so are taken and weighed before putting 

 on the funnel. Another portion is weighed out and 

 dried in the steam oven, to ascertain the proportion of 

 water in the sample. 50 c.c. of hot distilled water are 

 now poured on the soil, allowed to stand a few minutes, 

 and the pump started. When the liquid has been drawn 

 through, successive small portions of hot water are put 

 on, and the pump started afresh; it will be found 

 possible to wash out practically the whole of the nitrate 

 with 100 c.c. of water. 



