CALCAREOUS MANURES— THEORY. 37 



ground to receive it. The tube C is introduced into the lower orifice of A, and the 

 bladder connected with it placed in its tlaccid state into E. which is filled with water. 

 The graduated measure is placed under the tube of E. When the stopcockof B is 

 turned, the acid flows into A, and acts upon the soil ; the elastic fluid generated passes 

 through C into the bladder, and displaces a quantity of water in E equal to it in bulk, 

 and this water flows through the tube into tiie graduated measure; and gives by its 

 volume the indication of the proportion of carbonic acid disengaged from the soil ; for 

 every ounce measure of which two grains of carbonate of liuie may be estimated." — 

 Davy's Jgr. Chem. 



The correctness of this mode of analysis depends on two well-established 

 facts in chemistry: 1st, That the component parts of calcareous earth al- 

 ways bear the same proportion to each other, and these proportions are as 

 forty-four parts (by weight) of carbonic acid, to fifty-six of lime. 2d, 

 That the carbonic acid gas which two grains of calcareous earth will yield 

 is equal in bulk to one ounce of fresh water. The process, with the aid of 

 this apparatus, disengages, confines, and measures the gas evolved ; and for 

 evei'y measure equal to the bulk of an ounce of water, the operator has 

 but to allow two grains of calcareous earth in the soil acted on. It is 

 evident that the result can indicate the presence of lime in no other com- 

 bination except that which forms calcareous earth ; nor of any other earth, 

 except carbonate of magnesia, which, if present, might be mistaken for 

 calcareous earth, but, which is too rare, and occurs in proportions too small, 

 to cause any material error in ordinary cases, and in soils of this region. 



But if it be only desired to know whether calcareous earth is entirely 

 wanting in any soil— or to test the truth of my assertion that so great a 

 proportion of our soils are destitute of that earth— it may be done with far 

 more ease than by either of the foregoing methods, and without apparatus 

 of any kind. Let a handful of the soil (without drying or weighing) be 

 thrown into a large drinking glass, containing enough of pure .water to 

 cover the soil about two inches. Stir it until all the lumps have disappear- 

 ed, and the water has certainly taken the place of all the atmospheric air 

 which the soil had enclosed. Remove any vegetable fibres, or froth, from 

 the surface of the liquid, so as to have it clear. Then pour in gently- about 

 a table spoonful of undiluted muriatic acid, which by its greater weight 

 will sink, and penetrate the soil, without any agitation being necessary for 

 that purpose. If any calcareous earth is present it will quickly begin to 

 combine with the acid, throwing off its carbonic acid in gas, which cannot 

 fail to be observed as it escapes, as the gas that eiglit grains only of calca- 

 reous earth would throw out, would be equal in bulk to a gill measure. 

 Indeed, the product of only a single grain of calcareous earth, would be 

 abundantly plain to the eye of the careful operator, though it might be the 

 whole amount of gas from two thousand grains of soil. If no efferves- 

 cence is seen even after adding more acid and gently stirring the mixture, 

 then it is absolutely certain that the soil contained not the smallest portion 

 of carbonate of lime; nor of carbonate of magnesia, the only other substance 

 which could possibly be mistaken for it. 



The examinations of all the soils that will be here mentioned were made 

 in this pneumatic apparatus, except some of tliose which evidently evolved 

 no gas, and when no other result was required. As calcareous earth is 

 plainly visible to the eye in all shelly soils, they only need examination to 

 ascertain its proportion. A few examples will show what proportions we 

 may find, and how greatly they vary, even in soils apparently of equal value. 

 1. Soil, a black clayey loam, from the top of the high knoll at the end of 

 Coggins Point, on James-river, containing fragments of muscle shells 

 throughout. Never manured and supposed to have been under scourging 

 cultivation and close grazing from the first settlement of the country ; then 



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