502 



acid and carbonate of ammonia play in rendering soluble tlie mineral 

 elements of plant-food. Bat the paper will speak for itself, and we ask 

 fur it a careful i)erusal : 



The point of departure in my rescarclies is a work upon the black soils of Russia, 

 the fertility of wbich is well known. Havinji; at my disposition large samples taken 

 from a. vertical section of three meters (9 feet 9 inches) at Uladowka, (Podolie,) I hare 

 been able to make a complete examination of a soil wiiich, havinoj never received any 

 manure of any kind, and having been submitted to triennial rotation, j>rodnced for 

 several years 22 hectoliters (about 62.4 bushels) of oats and 30,000 kilograms ((i(j,000 

 pounds) of beets per hectare, (2.47 acres.) 



The chomical composition of these soils does not indicate a persistent fertility; and 

 it was to determine the cans? of this which led me to the results which form tlie sub- 

 ject of this memoir. The Ijlack soil owes its color and perliaps its fertility to a partic- 

 ular combination of the organic matters with silica, phosphoric acid, iron, lime, and 

 magnesia, which I have separated, and of which I shall descril)e the principal proper- 

 ties, united in the soil, in all probability, with earthy bases. This complex substance 

 is not i-emoved, in its natura state, either by <Vater, or by acid or alkaline solutions. 

 It is tirst necessary to destroy the calcareous combination in which it is engaged. We 

 may proceed in the following manner: treat the soil with a slightly acid solution, 

 wash by displacement in order to remove the excess of acid, moisten the residue with 

 ammonia, and exhaust the soil by continued washing with amuioniacal water. The 

 black matter is thus dissolved, tlie soil is comidetely decolorized, and its physical aad. 

 chemical properties sustain important modihcations. 



The dark-brown solution thus obtained, treated for the ordinary re-actions of fhos- 

 phorio acid, iron, magnesia, lime, and silica, does not indicate the presence of any of 

 these substances, which f;icts correspond with those observed by Th. de Saussure in 

 Lis classic researches upon the soils. 



Evaporated to dryness it gives a brilliant black residue, brittle and soluble in the 

 alkalies. When calcined this carbon leaves a red colcothar residue, whose coloration 

 and weight varj^ with the nature of the soil from which it is obtained. This carbon 

 Avill, as the case may be, give irom 2 to 60 per cent, of its weight of ash. Treated with, 

 uitric acid this residue is partially dissolved ; the soluble part consists of the phos- 

 phates of iron, manganese, lime, magnesia, and potassa. The part insoluble in uitric 

 acid is completely attacked by sulphuric acid. It consists of silicate of iron containing 

 a little silicate ot lime. I ccmsider it due to M. P. Thenard to recall here the important 

 part which he was led (in 1858,) according to his experiments to assign to the silicates 

 as solvents of the phosi)hates in the soil. 



As we have seen, ammonia, in cintain conditions, dissolves in the soil the phosphates 

 of iron, lime, magnesia, and silica iu a state of combination which chemistry has here- 

 toibre Ijeeu unalile to produce. 



The black soil which I have analyzed contains, per 100 grams of soil, 0.30 gram 

 of ]>hos)ilioric acid, of which 0.1(5 gram, that is to say 80 per cent., is iu a state easily 

 rendered assimilalde by vegetables, as we shall see further on. The soil of Russia 

 pi VPS p>r kilogram 42 grams of this black matter, leaving by calcination 21 

 grams of ash. 



liie analyses of different soils collected in my work and the comparison of the agri- 

 cultural products of these soils show that there is a close relation between the fertility 

 orf a soil and its richness iu matters soluble in ammonia, (especially phosphoric acid 

 in Ibis jartioular state.) 



What are the re-actions under whose influence the organic matter combined with 

 the earthy basis in the soil in nature are placed at the disposition of the roots of 

 Yegetal)les? The following facts s^em tome to otfer a satisfactory response to these 

 questions. I have asceitained that the intervention of a strong acid, such as 

 chlorhydiic, is unnecessary ; a dilute solution of oxalic acid will set free, in the soil of 

 Russia, the nnitter soluble in ammonia. When the black soil is treate<l with oxalic 

 acid, then with water, and finally with ammonia, we obtain a brown solution- con- 

 taining phosphoric acid, iron, lime, magnesia, ami silica, as with chlorhydric acid. 

 The oxalic aciil, which usually appropriates the calcareous elements of the soil, is un- 

 able to precii)itate the lime engaged in this organic combination. 



After having endeavored, without any decided sncct-ss, to sul)stitnte free carbonic 

 acid gas for oxalic acid, I have completely succeeded with carljonic acid, combined 

 •with an alkaline base, esjiccially with carbonate of a«Minionia ; a dilute solution of -this 

 salt passing slowly through a layer of black soil plays successively the part of an 

 acid ami tliat of a base, vis-a-vis, upon the black matter in question; at the begin- 

 ning of the eX[)orirn')nt thi c.ir'oo i iti is d >c ).n_» >sed, its carb >nic acid c:>:nbiiia-i with 

 the lime, which renders the black matter ot the soil insoluble; the animcmia thus set 

 free dissolves the black substance liberated from the lime, and the soil is decolorized ; 

 the deep-brown solution, evaporated to dryness, gives a red residue, (phos|)horic acid, 

 iron, lime, magnesia, and silica,) exactly analogous to that which 1 have described 



