ANALYSIS. 



pour. As generally obtained, silica 

 is held insoluble in water ; still, when 

 in a state of extreme subdivision, it 

 is soluble ; and then its insolubility is 

 probably not so absolute as is gener- 

 ally supposed, for M. Payen has found 

 notable quantities in the water of the 

 Artesian well of Grenelle, and in that 

 of the Seine. Silica exists especially, 

 in very appreciable quantity, in cer- 

 tain hot springs, where the presence 

 of an alkaline substance favours its 

 solution ; the water of the hot springs 

 of Reikuni in Iceland contain about 

 j-nL^th parts of its weight of silica ; 

 and the thermal spring of Las Trin- 

 cheras, near Puerto Cabello, depos- 

 ites abundant silicious concretions. 

 The water of this latter spring, which 

 is at the temperature of 210° Fahren- 

 heit, besides silica, contains a quan- 

 tity of sulphureted hydrogen gas, and 

 traces of nitrogen gas. Rock crystal, 

 when colourless and transparent, may 

 be regarded as pure silica ; in the va- 

 rieties of quartz which mineralogists 

 designate as chalcedony, agate, opal, 

 &c., the silica is combined with dif- 

 ferent mineral substances, particular- 

 ly oxide of iron and of manganese, 

 alumina, lime, and water. 



Carbonate of Lime, considered as 

 rock, belongs to every epoch in the 

 geological series, and frequently con- 

 stitutes extensive masses. When 

 pure, it is composed of lime, 563 ; car- 

 bonic acid, 437 ; and its density is 

 then from 27 to 2-9. It dissolves 

 with effervescence, without leaving 

 any residue in hydrochloric or nitric 

 acid. Exposed to a red heat, its 

 acid is disengaged, and quick-lime re- 

 mains. Carbonate of lime is insolu- 

 ble in water, but it dissolves in very 

 considerable quantity under the influ- 

 ence of carbonic acid gas. When 

 such a solution is exposed to the air, 

 the acid escapes by degrees, and the 

 carbonate is deposited, by which 

 means those numerous deposites of 

 carbonate of lime are produced which 

 we see constituting tufas and stalac- 

 tites. The solubility of carbonate of 

 lime in water acidulated with carbon- 

 ic acid enables us to understand how 

 plants should meet with this salt in 



the soil, inasmuch as rainwater al- 

 ways contains a little carbonic acid. 



The mineral substances which we 

 have now studied, taken isolatedly, 

 would form an almost barren soil ; 

 but, by mixing them with discretion, 

 a soil would be obtained presenting 

 all the essential conditions of fertil- 

 ity, which depend, as it would seem, 

 much less on the chemical constitu- 

 tion of the elements of the soil than 

 on their physical properties, such as 

 their faculty of imbibition, their den- 

 sity, their power of conducting heat, 

 &c. It is unquestionably by study- 

 ing these various properties that we 

 come to form a precise idea of the 

 causes which secure or exclude the 

 qualities we require in arable soils 

 This has been done very ably by ]\I 

 Schubler ; and his admirable papei 

 will remain a model of one applica- 

 tion of the sciences to agriculture.* 



The researches of M. Schubler were 

 directed to the mineral substances 

 which are generally found in soils, 

 viz. : 1st. Silicious sand ; 2d. Calca- 

 reous sand : 3d. A sandy clay con- 

 taining about xo't^is of sand ; 4lh. A 

 strong clay containing no more than 

 about yiyths of sand ; 5th. A sti!l 

 stronger clay containing no more 

 than about y^th of sand ; 6th. Near 

 ly pure clay ; 7th. Chalk, or carbon- 

 ate of lime in the pulverulent state ; 

 8th. Humus ; 9th. Gypsum ; 10th. 

 Light garden earth, black, friable, 

 and fertile, and containing, in 100 

 parts, clay 52-4, quartzy sand 365, 

 calcareous sand 1-8, calcareous earth 

 20, humus 7-3 ; 11th. An arable soil 

 composed of clay 51-2, silicious sand 

 427, calcareous sand 04, calcareous 

 earth 2-3. hunms 34; and, 12th. An 

 arable soil taken from a valley near the 

 Jura, containing clay 333, silicious 

 sand 630, calcareous sand 12, calca- 

 reous earth and humus 1 -2, loss 1 3. 



The object of these inquiries was 

 to ascertain, 1st. The specific grav- 

 ity of soils ; 2d. Their power of re- 

 taining water ; 3d. Their consist- 

 ency ; 4th. Their aptitude to dry ; 



* Schubler, Annals of French Agriculture, 

 vol. xl., p. 122, 2d series. 



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