343 MANURES. 



but we Icnow that there is no example of a vegetable organic tissas 

 from which they are completely excluded. 



The refuse of plants, the most amply endowed with azote, such as 

 cabbage, beet-root, beans, &c., are certainly those which are sus- 

 ceptible of the most rapid and complete putrid fermentation ; straw, 

 on the contrary, when alone, undergoes it slowly and imperfectly, 

 the small quantity of the azotic principle which it contains is chang* 

 ed, and reacts upon the ligneous particles which surround it ; but 

 the effect is soon arrested, and even ceases entirely, unless substances 

 richer in azote concur. The woody matter of the straw is exactly 

 in the condition of sugar which has not had a dose of ferment suf- 

 ficient for its total transformation into alcohol. 



Most organized substances, whether they belong to the animal or 

 vegetable kingdom when placed in certain conditions, undergo the 

 profoundest changes from the action of hydrogen ; these alterations 

 ought to be studied with all the more care, because in practical 

 agriculture we are interested successively in fostering or preventing 

 the causes which produce them, according as our object is to accele- 

 rate the decomposition of vegetable refuse for manure, or to adopt 

 the precautions which experience suggests, in order to preserve 

 the produce of our harvests unchanged. Organic substances moist- 

 ened and exposed to the air under a temperature, the minimum of 

 which (I believe after several experiments) may be fixed at 48° or 50" 

 F., seize upon the oxygen and absorb it, in part, in order to form water 

 with their hydrogen, and carbonic acid with their carbon. When 

 these substances are accumulated in a mass sufficiently great, the 

 heat produced is not rapidly dissipated, the temperature rises, and 

 promotes the reaction to such a degree as to produce active burning, 

 a conflagration, in place of the slow combustion manifested at first. 

 It is not very unusual to see hay, which had been gathered in too 

 damp a condition, take fire in the stack ; and the high temperature 

 acquired by wet rags placed in the fermenting vats of paper mills, 

 and the copious production of carbonic acid which results, show that 

 we are right in assimilating this kind of action to the phenomenon 

 of combustion. This sluggish combustion is not peculiar to azotized 

 organic substances : it takes place equally in those destitute of azote. 

 The alteration of organic matters, the combustion which goes on at 

 a low temperature by the action of the air, difi'ers in its results from 

 the decomposition which is effected in the midst of a liquid mass. 

 We have seen, for example, that gluten fermenting under water, 

 disengages hydrogen gas. Now Berthollet has established, and 

 Saussure has confirmed his observations, that an azotized body in 

 putrefaction, the whole of whose parts are in contact with the air, 

 never contributes either hydrogen gas or azote to the confined at- 

 mosphere in which it is placed ; and on the other hand, Saussure 

 has shown, that organic substances which do not emit hydrogen gas 

 during their spontaneous decomposition in a medium void of oxygen, 

 do not alter the volume of an atmosphere of which this gas forms a 

 purt; on the contrary, these sub tances condense oxygen as soon af 



