196 



Analyses of Ashes of Plants. 



correspondence to some accidental cause/* than to consider it as 

 destructive of the principle which we have before attempted to 

 elucidate ; namely, that in the entire plant the mineral matter 

 will be found far more constant in quantity and composition than 

 in either the root or the leaf taken separately — the variations 

 which occur being counteracted by the alteration of the per 

 centage of ash or of the proportion of root to leaf. 



One important point in reference to the mineral composition 

 of the carrot still remains to be noticed. A comparison of the 

 mineral contents of a ton of the entire crop of beet, turnip and 

 carrot, clearly shows (see page 199) that the carrot is fully 

 as rich in the more important elements of mineral fertility as 

 either of the other crops — indeed, if anything, rather surpasses 

 them ; for although it contain on the average a very slight pro- 

 portion less of phosphoric acid than turnips, yet it will be seen 

 on the other hand to possess more magnesia and more alkali than 

 either mangold-wurzel or turnip. For most practical purposes, 

 however, we may consider these three roots as equal in mineral 

 wants and peculiarities. The carrot, then, requires as much 

 mineral food as the turnip or beet-root. But this being the case. 



* The analysis of the leaves is subject to a source of error to which that 

 of the roots is not open ; the leaves are frequently not quite free from dirt, 

 which they have acquired from various causes. Every effort is made to 

 cleanse them perfectly, but the difficulty of accomplishing this is very 

 great ; and when it is considered how small is the proportion of ash in 

 comparison with the vegetable substance operated upon, it is easy to see 

 how the quantity of the former may in spite of all precautions be sensibly 

 augmented by small portions of foreign matter, which from their minute- 

 ness have escaped the strictest scrutiny. To this cause we are inclined to 

 attribute the very uniform relation which is observable in the analyses of 

 the ash of the leaf between the silica and peroxide of iron — wherever the 

 one is large, the other is large also. Now, as we have never been able to 

 discover alumina in very carefully prepared ashes (such as those of seeds), 

 we have not thought it worth while to embarrass our methods of analysis by 

 the separation of this body (should it happen to be present) from peroxide 

 of iron, which itself is a substance of little importance, and sometimes 

 scarcely detectible from the excessively minute quantities of it which are 

 resent in the ash— as may be seen by many of our analyses — under the 

 ead of peroxide of iron may sometimes then be included a little alumina, 

 and it is precisely these substances and silica, which a want of perfect 

 cleanliness of the leaf would introduce. 



In the present instance it is highly probable that this source of error 

 may have interfered ; for, by reference to the analysis, it will be seen that 

 the silica and peroxide of iron are both unusually high. It must, however, 

 be remembered that any accidental impurity of this kind only affects the 

 quantity of those substances of which any portion is so introduced : if 

 silica only is accidentally introduced, this will make no difference in the 

 quantity of any other body (as phosphoric acid or magnesia) in a given 

 weight of the vegetable, although the composition of the ash in 100 parts 

 is thereby altered. 



