810 APPEARANCE AND TESTING OF MARL. 



to be at such considerable distance. The upper layer, a (say, 

 for example, finely-rubbed-down fragments of shells, making 55 

 per cent, of the layer), may be 6 feet thick at one part, and only 1 

 foot or less at the other. The next layer, b (indurated or stony, 85 

 per cent, of carbonate of lime), may vary at the same two distant 

 places from 1 foot to 3. The next, c (sandy and fine, 20 per 

 cent.), is 4 feet in one digging, and runs out to nothing before 

 reaching the other. The next, d (firm, with entire shells, 40 per 

 cent.), is 7 feet in the one and but 3 in the other place. Now it 

 would require a careful analysis of each of these layers of different 

 qualities, and observation of their comparative thickness, to know 

 the average strength of the whole section of marl at one excava- 

 tion. But these same observations would usually serve for estimat- 

 ing nearly enough the averages of the like layers whenever they 

 were found and identified, by allowing for the changes in thickness 

 of each layer. 



Whoever uses marl ought to know how to analyze it, which 

 a little care will enable any one to do with sufficient accuracy. 

 The method described, at page 56, for ascertaining the propor- 

 tions 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 merely applying sufficient attention and care. To perform 

 this process will require no other chemical tests than muriatic 

 acid and carbonate of potash, and no apparatus, except correct 

 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 considera- 

 tion 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 dif- 

 ferent times muriatic acid diluted with three or four times its bulk 

 of water (ftny except lime-stone, or hard water.) The acid will 

 dissolve all the lime in the calcareous earth, and let loose the car- 

 bonic acid, with which it was previously combined, in the form of 

 gas ; or air, which causes the effervescence, which so plainly marks 



