92 THE ANALYSIS OF SOILS. V. 



purposes, thus dividing the soil into four parts. If further 

 separation is desired, elutriation must be resorted to, for 

 details of which a treatise on soil analysis should be consulted. 

 In some cases a microscopical examination of the various 

 sediments is made in order to determine their mineralogical 

 nature. For a purely chemical examination a sieve of 3mm. 

 and one of 1mm. perforations (practically ^in. and ^in.) are 

 all that are necessary. 



Chemical Analysis. A full chemical analysis of a soil, 

 including the determination of the quantities of every ingre- 

 dient, is rarely required. If it be, the "fine soil " passing the 

 3mm. sieve is reduced to fine powder, the particles of which 

 are, at least, able to pass the 1mm. sieve. 



Determination of Moisture. About 5 grammes of the air- 

 dried fine soil which has passed the 1mm. sieve are accurately 

 weighed in a flat-bottomed platinum dish previously weighed 

 with a short piece of stout platinum wire to act as stirrer. 

 The dish is heated to 100 in a steam bath for 12 hours, with 

 occasional stirring of its contents. It is then cooled in a desic- 

 cator and weighed, again heated for an hour, and re- weighed. 

 If the difference between the two weighings does not exceed 

 2mgm. the moisture is calculated from the loss in weight If 

 the difference between the two weighings exceeds 2m gin. the 

 dish is again heated for an hour at 100 and re-weighed until 

 two successive weighings show less difference. 



Determination of Loss on Ignition. The residue from the 

 moisture determination is heated to low redness, with occa- 

 sional stirring, until all black particles are destroyed. This 

 can very conveniently be done in a muffle furnace. The dish 

 is removed, allowed to cool, the contents moistened with 

 ammonium carbonate solution, dried, heated to about 150, 

 or even to low redness for a minute or two, again cooled and 

 weighed. The loss is equal to the organic matter and com- 

 bined water. The object of the treatment* with ammonium 

 carbonate is to restore any calcium carbonate (which would 



* Several errors in the determination of moisture are not adequately corrected for 

 by this treatment ; magnesia left from magnesium carbonate on ignition only very 

 slowly takes up carbon dioxide again ; so, too, lime present as calcium humate will be 

 converted into carbonate. These errors and others inherent in the method are small 

 and can usually be ignored. 



