MANURES. 43 



to the lime they yield ; and when containing the phosphate 

 in addition, their value is largely increased. The quantity 

 that may be advantageously used, is even more variable than 

 that of pure lime, inasmuch as the quality varies with every 

 bed in which it is found. They are adapted to the improve- 

 ment of all soils, unless such as are already sufficiently filled 

 with lime, and they are more generally useful to meadows 

 than the pure carbonate. Their benefits will be greatly en- 

 hanced, if the clay marl be used on light or sandy soils, and 

 sandy marls on clays and heavy lands. Marl has sometimes 

 been applied at the rate of 200 cubic yards per acre ; but 

 where it approaches to purity, and the soil is in the proper 

 condition to be benefitted, even four or five cubic yards may 

 be sufficient to produce the best effects. Circumstances 

 alone must determine the proper quantity to be used. Marl 

 should be carried out and exposed in small heaps, before 

 spreading on the land. Exposure to the sun, and especially 

 to the frosts of winter, is necessary to prepare it for use. 



Analysis of Marls. Marls may be readily analyzed 'by 

 any one, with a pair of accurate scales and weights and a 

 large-mouthed vial. To one part muriatic acid, add two 

 parts water, fill the vial to about one third, and balance it 

 on the scales. Then slowly add 100 grains of the pulver- 

 ized marl, thoroughly dried over the fire. When the effer- 

 vescence has subsided, expel the carbonic acid from the vial, 

 by pouring off, or blowing into the vial through a reed or with 

 a bellows, its greater weight causing it to retain its place 

 to the exclusion of the air. Now add weights to the oppo- 

 site scale till balanced, and the deficiency of grains under 

 100, will show the amount of carbonic acid expelled; and 

 as this is combined in the proportion of 46 to 54 of quick or 

 pure lime, in every 100, the loss indicates 46 per cent, of 

 the carbonate of lime contained in the marl. 



From the frequent presence of phosphate and sulphate 

 of lime, and sometimes potash and animalized matters in 

 marls, this kind of analysis seldom indicates the value of a 

 marl bed for agricultural purposes. If its exact worth is to 

 be ascertained, there must be a more perfect analysis, by an 

 experienced chemist. 



SHELL SAND. 



This is a calcareous sand, sometimes mixed with animal 

 matter and the phosphates. It abounds on some parts of the 

 coast of Cornwall, and on the western shores of Scotland, 



