70 



AGRICULTURAL CHEMISTRY 



certain cases in which nitrate of soda has I ent families of plants are distinguished by 

 failed, nitrate of potash (common saltpetre) ' containing certain acids, differing very mucn 

 has been very successful. Analyses of , in composition; and further, that these acids 



wheat grown with nitrate of soda and nitrate 

 of potash would be of interest, in order to 

 determine whether a mutual substitution of 

 their respective bases is effected. It is to be 

 hoped that future experiments will throw 

 more light upon the action of this interest- 

 ing manure, for theory cannot be satisfied 

 with those already existing. It has been 

 usual to employ a less quantity by weight 

 of nitrate of potash than of nitrate of soda. 

 This procedure seems rather empirical, for 

 unless sanctioned by experience, it would 

 d priori appear to be better to add the great- 

 est quantity of that salt which possesses the 

 highest equivalent. Now the equivalent of 

 nitrate of potash is considerably higher than 

 that of nitrate of soda. 



Charcoal in a state of powder must be 

 considered as a very powerful means of pro- 

 moting the growth of plants on heavy soils, 

 and particularly on such as consist of ar- 

 gillaceous earth.* 



Ingenhouss proposed dilute sulphuric acid 

 as a means of increasing the fertility of a 



do not exist in the juice in an isolated state, 

 but generally in combination with certain 

 alkaline or earthy bases. The juice of the 

 vine contains tartaric acid, that of the sorrel 

 oxalic acid. It is quite obvious that a pecu- 

 liar action must be in operation in the or- 

 ganism of the vine and sorrel, by means of 

 which the generation of tartaric and oxalic 

 acid is effected ; and also that the same ac- 

 tion must exist in all plants of the same 

 genus. A similar cause forces corn-plants 

 to extract silicic acid from the soil. The 

 number of acids found in different plants is 

 very numerous, but the most common are 

 those which we have already mentioned ; to 

 which may be added acetic, malic, citric, 

 aconitic, maleic, kinovic acids, &c. 



When we observe that the proper acids 

 of each family of plants are never absent 

 from it, we must admit that the plants be- 

 longing to that family could not attain per- 

 fection, if the generation of their peculiar 

 acids were prevented. Hence, if the pro- 

 duction of tartaric acid in the vine were ren- 



with this material. 100 parts of concen- 

 trated sulphuric acid diluted with from 800 

 to 1000 parts of water, are equivalent to 

 176 parts of gypsum. 



SUPPLEMENTARY CHAPTER. 



ON THE CHEMICAL CONSTITUENTS OF SOILS. 



soil. Now, when this acid is sprinkled on | dered impossible, it could not produce 

 calcareous soils, gypsum (sulphate of lime) grapes, or in other words, would not fructify, 

 is immediately formed, which of course Now the generation of organic acids is pre- 

 prevents the necessity of manuring the soils vented in the vine, and, indeed, in all plants 



which yield nourishment to men and ani- 

 mals, when alkalies are absent from the soil 

 in which they grow. The organic acids in 

 plants are very rarely found in a free state ; 

 in general, they are in combination with 

 potash, soda, lime, or magnesia. Thus, 

 silicic acid is found as silicate of potash, 

 acetic acid as acetate of potash or soda, 

 oxalic acid as oxalate of potash, soda, or 

 lime, tartaric acid as bitartrate of potash, 

 &c. The potash, sodT, lime, and magnesia 

 in these plants are, therefore, as indispensa- 



THE fertility of a soil is much influenced 

 by its physical properties, such as its poro- 

 sity, colour, attraction for moisture, or state 

 of disintegration. But independently of 

 these conditions, the fertility depends upon 

 the chemical constituents of which the soil 

 is composed. 



We have already shown, at considerable 

 length, that those alkalies, earths, and phos- 

 phates, which constitute the ashes of plants, 

 are perfectly indispensable for their deve- 

 lopement ; and that plants cannot flourish 

 upon soils from which these compounds are 

 absent. The necessity of alkalies for the 

 vital processes of plants will be obvious, 

 when we consider that almost all the differ- 



cellent manure for his land. The crops obtained 

 by means of it presented the same general charac- 

 ters as those manured with nitrate of potash, and 

 exhibited a greater intensity of colour. If this is 

 found uniformly to be the case, it will very much 

 strengthen the supposition that the action of ni- 

 trate of soda is due to its alkaline constituent. 

 ED. 



* For much valuable information on the sub- 

 ject of manures, see " Agricultural Chemistry," 

 vol. viii. of Sir H. Davy's collected Works. 



ble for their existence as the carbon from 

 which their organic acids are produced. 



In order not to form an erroneous conclu- 

 sion regarding the processes of vegetable 

 nutrition, it must be admitted that plants re- 

 quire certain salts for the sustenance of their 

 vital functions, the acids of which salts exist 

 either in the soil (such as silicic or phos- 

 phoric acids) or are generated from nutri- 

 ment derived from the atmosphere. Hence, 

 if these salts are not contained in the soil, or 

 if the bases necessary for their production 

 be absent, they cannot be formed, or in other 

 words, plants cannot grow in such a soil. 

 The juice, fruit, and leaves of a plant can- 

 not attain maturity, if the constituents ne- 

 cessary for their formation are wanting, and 

 salts must be viewed as such. These salts 

 do not, however, occur simultaneously in 

 all plants. Thus, in saline plants, soda is 

 the only alkali found ; in corn plants, lime 

 and potash form constituents. Several con- 

 tain both soda and potash, some both potash 

 and lime ; whilst others contain potash and 



rw^i i " M 



magnesia. The 

 manner. Thus 



acids vary 

 plant 



one 



may 



s imilar 

 contain 



