No. v.] OP THE ORGANIC MATTKR PRESENT IN THE SOIL. 31 



s'rable to ascertain how much humic acid a soil contains in a state in which it 

 is soluble in water. Where ammonia, potash, or soda is present in the soil, 

 some chemists consider this quantity to be very considerable, and to exercise 

 an important influence upon vegetation. 



That which was taken up by water from the dried residuum is again to be 

 evaporated to dryness, dried at 150°, weighed, and burned at a low red heat. 

 The loss is organic matter, and may have been crenic or apocrenic, or some 

 other of the organic acids formed in soils, the compounds of which, with lime, 

 alumina, and prot-oxide of iron, are soluble in water. If any little sparkling or 

 burning like match-paper be observed during this heating to redness, it maybe 

 considered as an indication of the presence of nitric acid — in the form of ni- 

 trate of potash, soda, or lime. In this case the loss by burning will slightly ex- 

 ceed the true amount of organic matter present, owing to the decomposition and 

 escape of the nitric acid also. The mode of estimating the quantity of this acid, 

 when it is present in any sensible proportion, will be hereafter described. 



2'^. The caustic potash employed to dissolve the insoluble humus (11") takes 

 up also any alumma which may have been in combination with the humic 

 acid or may still remain united to the mudesous* or other organic acids. When 

 the solution is filtered and the humic acid separated by the addition of muriatic 

 acid till the liquid has a distinctly sour taste, this alumina, and the acids with 

 which it is in combination, still remain in solution. After the brown flocks of 

 humic acid, however, are collected on the filter, the alumina may be thrown down 

 from the filtered solution by adding caustic ammonia to the sour liquid, until 

 it has a distinctly ammoniacal smell. The light precipitate which falls must 

 be collected on a filter and washed with hot water till the potash is as completely 

 separated as possible. It is then to be dried at 300'^ F., weighed and heated 

 for some time in a close crucible over the lamp, at a temperature which begins 

 to discolour it, and again weighed. Being now burned in the air till it is quite 

 white, and weighed, the last loss may be considered as mudesous or some simi- 

 lar acid. 



The reason why this second method of drying over the lamp is here re- 

 commended, is, that alumina and nearly all its compounds part with their 

 water with great difficulty, and even with the precautions above indicated, it is 

 not unlikely that a larger per-centage of organic matter may thus be indicated, 

 than in reality exists in the soil. The check which the accurate experimenter has 

 upon all these determinations is this, that the sum of the several weights of the 

 humic acid, the insoluble humus, the vegetable fibre, and of the crenic and mu- 

 desous acids, if present, should be somewhat less than tliat of the whole com- 

 bustible organic matter, as determined by burning the dry soil in the open air 

 (9"). This quantity we have seen to be in most cases greater than the truth, 

 b'^cause any remainmg water or any nitric acid the soil may contain, are at the 

 same time driven off*. 



I may further remark upon this subject that the quantity of alumina thus 

 dissolved by the caustic potash is in most soils very small, and the quantity of 

 organic matter by which it is accompanied in many cases so minute, that the 

 determination of it may be considered as a matter of curiosity, rather than one 

 of practical importance, 



HI. — OF THE SOLUBLE SALINE MATTER IN THE SOIL. 



13*^. With a view to determine the nakire of the soluble saline matter in the 

 soil, a preliminary experiment must be made. An unweighed portion must be 

 introduced into five or six ounces of boiling distilled water in a flask, and kept 

 at a boiling temperature, with occasional shaking for a quarter of an hour. It 

 may then be allowed to subside, after which the liquid is to be filtered till it 

 passes through clear. It is then to be tested in the following manner. Small 



 Except where gyp.sum is present in the insoluble portion, which is n^jnfrequently the 

 case, when the loss will be partly water — since gypsum, after being driest 250°, loses still 

 about 20 8 per cent, of water when heated to redness. 



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