152 



CALCAREOUS MANURES— PRACTICE. 



white shells are rapidly reduced, after being mixed with an acid soil ; but 

 some gray kinds, as the scallop and the oyster, are so hard as to be very 

 long before they can act as manure. Some beds, and they are generally 

 the richest, have scarcely any whole shells, but are formed principally of 

 small broken fragments. Of. course the value of marl as a manure de- 

 pends in some measure on which kinds of shells are most numerous, and 

 their state of division, as well as upon the total amount of the calcareous 

 earth contained. The last is however by far the most important criterion 

 of value. The most experienced eye may be much deceived in the 

 strength of marl ; and still more gross and dangerous errors would be made 

 by an inexperienced marler. The strength of a body of marl often 

 changes materially in sinking a foot in depth — although the same changes 

 may be expected to occur very regularly, in every pit sunk throwgh the 

 same bed. Whoever uses marl ought to know how to analyze it, which 

 a nttle care will enable any one to do with sutlicient accuracy. The me- 

 thod described, at page 35, for ascertaining the proportions of calcareous 

 earth in soils, will of course serve for the same purpose with marl. But as 

 more particular and minute directions may be necessary for many persons 

 who will use this manure, and who ought to be able to judge of its value, 

 such directions will be here given, and which any one can follow by mere- 

 ly applying sufficient attention and care. To perform this process will re- 

 quire no other chemical tests than muriatic acid and carbonate of potash, 

 and no apparatus, except small scales and weights, a glass funnel and 

 some blotting or very porous printing paper— all of which may be bought 

 at any apothecary's shop. 



Directions for analyzing marl by solution and precipitation. 



1st. Take a lump of marl, fossil shells, &c., large enough to furnish a 

 fair sample of the particular body under consideration— dry it perfectly 

 near the fire— pound the whole to a coarse powder (in a metal mortar,) 

 and mix the whole together. Take from the mixture a small sample, 

 which reduce to a finely divided state, and weigh of it a certain portion, 

 say 50 grains, for trial. 



2d. To this known quantity, in a glass, pour slowly and at different times 

 muriatic acid diluted with three or four times its bulk of water — (any ex- 

 cept limestone, or hard water.) The acid will dissolve all the lime in the 

 calcareous earth, and let loose the carbonic acid, with which it was pre- 

 viously combined, in the form of gas, or air, which causes the effervescence, 

 which so plainly marks the progress of such solution. The addition of the 

 muriatic acid must be continued as long as it produces effervescence ; and 

 but very little after that effect has ceased. The mixture should be well 

 and often stirred, and should have enough excess of acid to be sour after 

 standing thirty or forty minutes. (So much of the acid as the lime com- 

 bines with loses its sour taste, as well as its other peculiar qualities.) 



The mixture now consists of 1, the lime combined chemically with 

 muriatic acid, forming muriate of lime, which is a salt, and which is dis- 

 solved in the water— 2, a small excess of muriatic acid mixed with the 

 fluid — and 3, the sand, clay and any other insoluble parts of the sample of 

 marl. To separate the solid from the fluid and soluble parts is the next 

 step required. 



3rd. Take a piece of filtering or blotting paper, about six or eight inches 

 square, (some spongy and unsized newspapers serve well,) fold it so as to 

 fit within a glass funnel, which will act better if its inner surface is fluted. 

 Pour water first into the filter, so as to see whether it is free from any hole. 



