98 EXPRESSIONS USED IN SOIL ANALYSES. 



rule, a high content of moisture is accompanied by a high percentage 

 of organic matter and of total nitrogen. 



3. .Loss on ignition. This includes the organic matter and com- 

 bined water present. Consequently it is high in soils containing much 

 humus or in those rich in hydrated silicates (chiefly clay). 



4. Insoluble matter. This the mineral matter which resists the 

 action of boiling strong hydrochloric acid for forty-eight hours may 

 be taken as sand. It usually contains some difficultly decomposable 

 silicates, but they must be of such a refractory character that they 

 are useless as sources of potash or lime to plants. In sandy soils the 

 quantity is high, sometimes amounting to 90, 95, or even 97 per cent 

 of the total, while in clayey soils it usually ranges from 55 to 75 per cent. 



5. Iron oxide and alumina. This item is of no great import- 

 ance as affecting the power of a soil to supply plant food, but some- 

 times, since it depends upon the clay present, affords useful information 

 as to the physical properties. 



If separate determinations of the oxide of iron and alumina be 

 desired, recourse must be had to any of the usual methods of separation 

 described in manuals of analytical chemistry. A high figure may 

 result from the presence of much ferric oxide in the soil, or in other 

 cases it may be due to a large proportion of clay. If to the latter 

 cause, the soil is generally also found to be well supplied with potash. 



6. Lime. The quantity given in an analysis conducted as described 

 includes all the lime present as carbonate, phosphate and humate and 

 a large proportion of that occurring as silicate. Its amount is of great 

 importance, affording valuable information as to the probable fertility 

 and manurial needs of a soil. If its amount be below 0*2 per cent, it 

 may be assumed in most cases, that liming the soil would be advisable ; 

 but much depends upon the relative proportions of the other constitu- 

 ents present. Thus, in a very sandy soil, containing say 95 or 96 per 

 cent of insoluble matter, 0'2 per cent of lime would be a relatively 

 large amount, while in a peaty or clayey soil the same percentage of 

 lime would be comparatively small. 



In some cases, a determination of the lime existing as carbonate is 

 useful. For methods of making such a determination, a manual on 

 chemical analysis should be consulted. 



7. Magnesia. This constituent, though essential to plants, is 

 usually sufficiently abundant in soils, occurring as carbonate associated 

 with limestone and also in many silicates. Much work has recently 

 been done in determining the most suitable ratio between the amounts 

 of lime and magnesia in soils. This depends upon various circum- 

 stances, but, generally speaking, it is found desirable that the percentage 

 of lime should exceed that of magnesia. 



8. Potash. This is usually the total amount of potash which can 

 be extracted by prolonged treatment of the powdered soil with strong 

 hydrochloric acid, and may safely be taken as a measure of the total 

 quantity which the soil can yield to crops for many years to come. 

 No doubt some potash in the form of refractory silicates remains in the 

 "insoluble matter '' and may be determined by the methods used for 

 estimating potash in silicates, but such potash has probably no agricul- 



