SUPERPHOSPHATE OF LIME. 105 



the atmosphere ; and even nitrog'en and its combinations 

 may l)e thus furnished. The avenues through which this 

 atmospheric supply is furnished, are the leaves of the plant ; 

 and their size aiford a correct criterion; ca'to'ls paribus, of 

 the amount of nutriment derived from the aerial source. 

 Thus beans and other pulse obtain more food from the 

 atmosidiere than cereal plants ; roots, more than the former ; 

 and Avheat, from the small size of the leaves, less than any. 

 Thus only can we account for the striking- fact, that if we 

 give a g'ood supply of inorg;anic elements oul)/ to the turnip- 

 crop, we shall very probably have a plentiful crop ; whilst, 

 if these be absent, however rich the manure may otherwise 

 be, the crop will be a failure. Not that we must therefore 

 draw the conclusion, that the org-anic manures are of little 

 or no importance to root-crops : they are of value, and par- 

 ticularly to the grain-crops which succeed. 



The organic matter which composes about one-third the 

 substance of bones is, however, so intimately combined with 

 the earthy portion, and their disunion is accomplished with 

 such diificulty, that the g'ood effects of either are to a certain 

 extent neutralized, at least so far as the first crop is con- 

 sidered ; and we are consequently oblig-ed to supply five or 

 six times as much as the crop actually requires, and to 

 render them available by means of pulverization. It is on 

 this principle that the assistance of sulphuric acid is sought 

 for and obtained : it serves, by its chemical affinities, to 

 separate the component parts of the bones, and render them 

 more soluble and available as food for plants. In the excel- 

 lent and accm-ate experiments of Mr. Hannam, related in a 

 former number of the Journal, it was clearly proved that 

 fresh bones, when g-round, were superior to boiled ones, from 

 which the fat was extracted ; and the latter were superior 

 to burnt bones, from which the g-elatine was also removed. 

 This result was, however, far more striking- when the bones 

 were dissolved in sulphuric acid, a difference of nearly 2 

 tons of turnips being- observed, whilst, with the bones merely 

 ground, a difference of 17 cwt. only was exhibited. From 

 the same experiment, we likewise learn that the beneficial 

 effects derived from the earthy part of bones are 4|- times 

 greater than that derived from the org-anic parts. I refer 

 to the Journal for the particulars of these experiments, and 

 to the previous number for other statements, from which, if 

 we had no other evidence, "we should be justified in drawing* 

 the conclusion, that 20-?. laid out in bones and acid will q:o 



