ANALYZING OP MARL. 313 



glass of water, and, after letting it stand a minute, for the sand to 

 subside, pouring off the fluid, with the lighter and still floating clay, 

 into another glass. The sand will be left, and the clay will be 

 poured off with the water ; and each may be collected on filtering 

 paper, dried, and weighed separately. 



The proportion of carbonate of lime in marl may also be conve- 

 niently and correctly determined by the diminution of weight from 

 the escape of the carbonic acid ; the quantity of which is always 

 in an invariable proportion to the lime with which it is combined. 

 For this purpose, weigh (in a thin and open-mouth vial) a certain 

 quantity (say 200 grains) of muriatic acid. Then of well dried 

 and powdered marl, weigh half as much (100 grains), and then add 

 the weighed marl, very slowly and gradually, to the acid. After 

 all effervescence has ceased, the whole will fall short of the original 

 weights (300 grains), by that of the carbonic acid evolved. This 

 bears the fixed proportion (very nearly) to the carbonate of lime, 

 of 45 parts in the 100. Therefore for every 4.5 grains weight 

 lost, estimate 10 grains of carbonate of lime in the marl tried. 

 (Davy.) ' 



For want of attention to the only safe guide, the chemical analy- 

 sis of marl, gross errors are often committed, and losses continually 

 sustained. By relying on the eye only, I have known marl, or 

 rather a calcareous sand, to be rejected as worthless, and thrown 

 off at considerable cost of labour, to uncover worse marl below, in 

 which whole shells were visible ; and on the contrary, earth has 

 been taken for marl, and used as such, which had no calcareous 

 ingredient whatever. The best marls for profitable use are gene- 

 rally such as show the fewest whole shells, or even large fragments, 

 and would be passed by unnoticed in some cases, or considered 

 only as barren sand, or equally worthless clay. But even if such 

 mistakes as these are avoided, every farmer using marl, without 

 analyzing specimens frequently and accurately, will incur much loss 

 by applying it in quantities either too great or too small. 



Distant transportation of Marl. 



An interesting question respecting the expense of this improve- 

 ment is, to what distance from the pit may marl be profitably 

 carried? If the amount of labour necessary to carry it half 

 a mile is known, it is easy to calgfclate how much more will be 

 required for two or three miles. The cost of teams and drivers is 

 in proportion to the distance travelled; but the pit and field labours 

 are not affected by that circumstance. At present, when so much 

 poor land, abundantly supplied with fossil shells, may be bought at 

 from two dollars to four dollars the acre, perhaps a farmer had bet- 

 ter buy and marl a new farm, than to move marl even three miles 

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