370 VARIOUS NATURAL FORMS OF CARBONATE OF LliME. 



slaked — meaning by this the compound of hydrate with carbonate — of 

 carbonate^ or of 'Bi- carbonate of magnesia, the latter of which is so- 

 luble in water to a very considerable extent. (It dissolves in 48 times 

 its weight of water — or a gallon of water will dissolve 5 ounces of 

 the Bi-carbonate containing 1^ ounces of magnesia.) 



§ 5. Of the various natural forms in which carbonate of lime is 

 applied to the land. 



In the unburned or natural state, lime is met with on the earth's 

 surface in numerous forms — in many of which it can be applied 

 largely, easily, and with economy to the land. 



1°. Marl. — Of these forms that of marl occurs most abundantly, 

 and is most extensively used in almost every country of Europe. By 

 the term marl, is understood, as I explained to you, when treating of 

 soils (Lee. XL, § 3,) an earthy mixture, which contains carbonate of 

 lime, and effervesces more or less sensiljly when an acid (vinegar or 

 diluted muriatic acid — spirit of salt) is poured upon it. Generally, 

 also, the tenacious marls, when introduced into water, lose their co- 

 'herence, and gradually fall to powder. This test is often employed 

 to distinguish between marly and other clays, yet the falling asunder, 

 though it afford a presumption, is not an infaUible proof that the sub- 

 stance tried is really a marl. 



Marls are of various colors, white, grey, yellow, blue, and of various 

 'degrees of coherence, some occurring in the form of a more or less fine, 

 loose, sandy powder, others being tenacious and clayey, and others, 

 again, hard and stony. These differences arise in part from the kind 

 and proportion of the earthy matters they contain, and in part, also, from 

 the nature of the locality, moist or dry, in w^hich they are found. The 

 hard and stony varieties are usually laid upon the land, and exposed to 

 the pulverising influence of a winter's frost before they are either spread 

 over the pasture or ploughed into the arable land. Some rich marls 

 consist in part or in whole of broken and comminuted shells, which 

 clearly indicate the source of the calcareous matter they contain. 



COMPOSITION OF MARLS FROM 



Lureburg. Osnabruck Magdeburg. Brunswick. Wesermarsh. Brunswick. 



powdery, stony. clayey. loamy. powdery. stony. 



auartz-Sand& Silica.. 56 230 58-4 734 789 7M 



Alumina 04 100 8-4 1-9 31 40 



Oxides of Iron 42 1-9 67 32 38 65 



Do. of Magnesia trace trace 03 03 03 1-1 



Carbonateof Lime.... 85-5 350 18-2 181 8-2 133 



Do. of Magnesia 1-25 09 38 1-5 3-0 26 



Sulphuret of Iron _ 7.3 _ _ — _ 



""tnldtuhtnir:} «-»5 'race 1-6 08 0-9 02 



Common Salt 0-03 trace trace trace 01 trace 



Gypsum 0-06 0-9 2-1 01 05 trace 



Phosphate of Lime } 3.3 ^.^ ^.^ ^.^ ^.^ ^.3 



(bone earth) j 



Nitrate of Lime 001 — — - — 



carbon 



Organic Matter 0-6 205 _ — — — 



100 100 100 100 100 100 



