

INSOLUBLE SUBSTANCES NOT SO USEFUL. 23 



nothing to water or even to concentrated muriatic acid, the 

 roots of plants have been found by experiment to be capable 

 of extracting from it lime, soda, magnesia, and other substances 

 which are necessary to their growth. This is believed to be 

 owing to the decomposing action of water and carbonic acid 

 in the soil, by which its rocky particles are decomposed and 

 resolved into their constituent parts, and thus made to yield them 

 in a soluble state to the roots. 



It is necessary, however, in all field experiments, to make use of 

 such substances only as are more or less directly soluble in water. 

 And when mixtures of substances are employed, they ought to 

 be in such a state of chemical combination, as not to act upon 

 and render one another insoluble. Where these two rules are 

 neglected, the immediate action of the single substance, or of the 

 mixture employed, is not to be depended upon, and may not 

 become sensible within a given time. It is scarcely possible to 

 judge of the effect of an application which is not in a condition 

 to act immediately, and to expend its action within a known 

 period ; to compare it with the action of other substances ; or to 

 say how far it is a profitable one, and ought to be repeated or 

 discontinued. Patents have been taken out in this country for 

 artificial manures, the peculiarity of which was, that such of 

 their constituents as were readily soluble in water, should by 

 art be rendered very sparingly soluble, and thus be liberated 

 slowly in the soil, and slowly worked up by the plant. But 

 the principle was a bad one, and hence the want of success 

 which has attended both the manufacture and the numerous 

 trials from time to time made with the manure. 



The suggester of experiments, therefore, must know what 

 compounds of each of the substances which are present in the soil 

 and in the plant are soluble ; to what extent they are soluble ; and 

 in what way they mutually affect the solubility of each other 

 when mixed together in the soil or in an artificial manure. 

 Thus he will know how to feed his plants; when, and with what, 

 they have been fed; and how to judge of an experimental trial 

 how far it has succeeded, or what may be the cause of its 

 failure. 



