37 J AGltlCULTLUAL MUSEUM. 



lAmc 13 a substance whosG external ciiarp,ct( rs n.rd 

 mode of production ai'c \vc!I kno^vn. It dif'Vrs iVnni 

 chalk and powdered limestone, chieilj^- by (he absenec 

 of fixed air, which is expelled from these dunn;j: th.clr 

 calcination. This air it f^rcediiy re absorbs from tlie at- 

 mosphere, and ail other bodies with vvhicli it comes iti 

 ccnlact, and wiilch can farnish It : but it cannot unite 

 with the air unless it is previously moistened One hnsi- 

 dred parts quick lime absorb about 28 of wafer. It is 

 soluble in aboiit 700 parts of this fluid. To regain its full 

 portion of air from the atmosphere, it requires a year or 

 more, if not purposely Sjircad out: it resists putrefac- 

 tion; but with the assistance of moisture it resolves or- 

 ganic substances into a mucous. 



3Iarl is of three sorts ; calcareous, argillaceous and Fi- 

 licioiis or sandy. AM are mixtures of mild calx (i.e. 

 chalk) with clays in such a manner as to fall to pieces by 

 exposure to the atmosphere, more or less readily. 



Calcareous Miui IS that which is moft commonly un- 

 derstood by the term Marl without addition. It is gene, 

 rally of a yellowish white or yellowish grey colour ; rare- 

 ly brown or lead coloured; it is seldom found on the 

 (surface of land, but commonly a few feet under it, and 

 on the sides of lulls, or rivers that flow through calearc- 

 ous countries, or under turf in bogs — frequently of a 

 loose texture, sometimes moderately coherent; rarely of a 

 stony hardness, and lience called ^toncmarl — sometimes 

 of a conipaet, sometimes of a lamellar texture, often so 

 thin as to be called paper ?;2arZ. ]t often abounds -with 

 shells, and then is called shell marl ; which is looked up- 

 on as the best sort. When in powder it feels dry be. 

 tween the fingers ; put in water it quickly falls to peiccs 

 or powder, and does not form a viscid mass. It chips 

 and moulders by exposure to the air and moisture, soon, 

 cr or later, according to its hardness and the proportioQ 

 of its ingredients ; if heated it will not form a brick bv^ 

 rather lime. Itcifcrvcsces with all acids. It consists o£ 

 from 33 to 80 per cent of mild calx, and from 06 to '^ 

 per. cent, of clay. 



