VI. ] METHODS OF ANALYSIS 147 



cases these may be omitted. It is occasionally desirable 

 to examine the soluble salts in the soil ; about 200 

 grams of the fine earth should be successively washed 

 with small portions of hot water by the aid of a 

 filter -pump. In the solution the total solids are 

 determined ; they consist, in the main, of the nitrates, 

 sulphates, and chlorides of sodium, potassium, mag- 

 nesium, and calcium, which can be determined by 

 the usual methods. Of course, the amount of soluble 

 salts to be found in the surface soil at any time is 

 largely regulated by the previous weather ; after con- 

 siderable rainfall the soluble salts are washed down 

 into the subsoil, after long evaporation they are con- 

 centrated in the surface layers. The amount of nitrates 

 that is present is further affected by the previous 

 cropping, temperature, and working of the soil, and 

 by the manipulation the soil receives after it reaches 

 the laboratory. Thus the determination of the soil 

 constituents that are soluble in water does not enter 

 into the ordinary routine of analysis, their presence 

 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 

 and 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 ordinary soils. 



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 



