No. 105.] 431 



The vegetable acids are valuable as a means of rendering soluble 

 certain earthy matters of the soil, whereby they become capable 

 of entering into the sap vessels of plants, and there undergo such 

 elaboration as may be suited to the wants of the plant. The most 

 valuable acids are those which contain the largest proportion of ni- 

 trogen, and at the head of the list stands the apocrenic acid, which 

 contains 17 per cent, of nitrogen. 



It is essential to the durability of a manure, as also to the healthy 

 growth of plants, that manures should not be too soluble, and this 

 acid and its salts, especially its combination with lime, possesses the 

 right degree of solubility, and its aluminous and ferruginous salts yield 

 the acid slowly and gradually to the carbonate of ammonia or to the 

 fixed alkalies, potash and soda. 



Animal matters, when they decay, undergo a more rapid putrefac- 

 tion, and the first product is ammonia. This gas is readily separated 

 from the putrescent matter by the action of hydrate of lime. When 

 the putrefaction or disorganization of animal matter is completed, a 

 black mould is formed, which consists of organic acids, united with 

 ammonia, and the salts which existed in the animal matter, are eith- 

 er converted into other salts, or they remain undecomposed, accord- 

 ing to the play of aflftnities in each case. 



Owing to the formation of ammonia by decomposing anima ma 

 ter, it is found advantageous to mix animal manures with all v (<, et 

 ble substances in forming composts ; and, since peat posseses r. nt 

 septic properties, it is proper in the spring season to mix hydrate o 

 lime with the compost, in order to complete the decomposition. B 

 this operation the ammoniacal gas is set free and penetrates ever 

 part of the compost heap, and if due care is taken to cover the hea 

 with peat, or with a layer of gypsum, no ammonia will be lost. 



Having explained, in some measure, the changes which organic 

 matters undergo while decomposing, I w^ould next give some account 

 of the acids which ultimately result from the process. Formerly, the 

 organic matter of mould was called ulmine and ulmic acid, from its 

 resemblance to the substance exuded by disease in the elm tree. 



Subsequently, Berzelius examined this matter, and divided ulmine 

 into three distinct substances, which he called geine and geic acid, 

 and apotheme. (See Traite Elementaire de Chimie, T. V., page 549, 

 and T. VI, page 573.) Lately that distinguished chemist has aban- 

 doned the names geine, geic acid and apotheme, and has given new 

 names to the substances of which his old geine was found to be com- 

 posed. 



Humus or mould is now found to consist of the following acids, 

 united to various bases. They were discovered and named by Ber- 

 zelius and Hermann : 



1. Crenic acid ; 



2. Apocrenic acid ; 



3. Humic acid ; 



4. Humin : 



