GREEN SAND. 



GREEN SAND. 



mospheric agents. Independently, however, 

 of the proof of its decomposition by its induc- 

 ing increased fertility, and of the mode by 

 which nature, operating with feeble agents 

 during a lengthened period of time, produces 

 great results, it may be shown that it is more 

 readily decomposed than is generally admitted. 

 William M. Uhler, in conjunction with the 

 author of this memoir, has lately been engaged 

 in making a series of experiments on this sub- 

 ject, which, although incomplete, nevertheless 

 afford sufficient grounds for drawing a few 

 conclusions. Dilute acetic acid decomposed 

 green sand after the lapse of a week or more ; 

 oxalic acid produced the same result in a few 

 days, and in the course of two weeks nearly 

 all the green sand had disappeared, and the 

 yellow oxalate of iron precipitated. But the 

 most surprising effects were produced by the 

 action of carbonic acid, one of the feeblest 

 known to the chemist, the use of which for this 

 purpose was first proposed by Mr. Charles Ro- 

 berts, of Philadelphia. By a well-charged so- 

 lution of this acid a large portion of the sand 

 was decomposed in a few days, and a weak 

 solution induced the same effects in the course 

 of a few weeks. Although few experiments 

 were made to determine quantitatively the re- 

 lative amounts of the constituents taken up by 

 the acids, yet the qualitative tests were suffi- 

 cient to show that all the ingredients were se- 

 parated from each other, and that the green 

 sand might be analyzed even by the feeble 

 operation of carbonic acid. 



"As the present state of our knowledge of 

 these subjects is limited when compared with 

 that advanced stage which we firmly believe 

 chemistry will produce in process of time, it 

 would be presumption to make unhesitating 

 assertions relative to the modus operandi of 

 organic and inorganic manures; we may, ne- 

 vertheless, and indeed we ought to draw such 

 inferences as are consistent with our present 

 knowledge of facts. The potassa of the green 

 sand appears to act on organic matter in the 

 soil by catalysis forming soluble salts of po- 

 tassa; the protoxide of iron acts in a similar 

 manner, but is itself changed to a less soluble 

 compound; and the alumina probably has a 

 similar action, proportional to its feeble affini- 

 ty. To the question that, since potassa acts in 

 this manner, why does not a large quantity of 

 green sand produce excessive luxuriance] it 

 may be answered, that it does where the quan- 

 tity is very large, but that its action is modified 

 and extenuated by the difficulty with which the 

 marl is decomposed, and by the presence of 

 other bases besides potassa. When green sand 

 is decomposed by nature or in the laboratory, 

 a small quantity of silica is taken up, and even 

 this substance, by forming a salt with crenic 

 acid, may assist in increasing fertility, as it is 

 an essential constituent of plants. 



" There are two points touching the theory 

 of the operation of green sand, which remain 

 to be noticed, the first of which is, that when 

 its decomposition has commenced, it advances 

 in an increasing ratio ; and the second, that 

 the constituents of green sand in their nascent 

 state, tfcat is, at the moment of their disengage- 

 ment from the compound, act with much 

 59* 



1 greater energy. Thus it would appear, then, 

 | that all the constituents of the marl exercise 

 an influence in promoting vegetation; and this 

 I action must take place in proportion to their 

 respective affinities, potassa being the most 

 powerful, followed by lime, magnesia, protox- 

 ide of iron, alumina, and silica; that the first 

 four assist in the generation of organic acids, 

 with which they and a small portion of alumina 

 and silica combine to form salts of different 

 degrees, but generally of difficult solubility, 

 which nourish and invigorate nascent vegeta- 

 tion ; that by the presence of a large portion 

 of bases which will form salts of difficult solu- 

 bility, a more prolonged and healthy action is 

 insured. 



" The above remarks relative to the mode 

 of operation of marl, apply equally to the seve- 

 ral varieties, as far as relates to the content of 

 green grains, but the calcareous species owe 

 their action partly to lime, in proportion as its 

 carbonate exists in the marl. When phosphate 

 of iron occurs in quantity, some notice must 

 be taken of its probable influence, for in regard 

 to it, we can only reason from theory, since it 

 has never been applied directly to land, with^ 

 the view of ascertaining its effects on vegeta- 

 tion. It appears from the analyses of Berthier, 

 that both phosphate of lime and of iron exist 

 in appreciable quantity in the ashes of plants; 

 for, in the composition of oak ashes, he divides 

 the 7 per cent, of phosphoric acid between 

 lime and iron in such a manner as to form 

 nearly 14 per cent, of phosphate of lime, and 

 ^ per cent, of phosphate of iron ; and in other 

 cases he gives the amount of the salt of iron 

 as high as 9 per cent.; and we believe from 

 experience that the utility of bone manure is 

 largely due to its phosphate of lime ; and hence 

 we may infer that the marl alluded to may be 

 serviceable, or even very valuable, from its 

 phosphate of iron ; and that if it were mingled 

 with a little lime, where it is wanting in the 

 marl, the atmospheric and humic agents, if the 

 expression be allowed, will cause such a trans- 

 mutation of the constituents as to bring both 

 phosphates to exert their influence in advanc- 

 ing the growth of plants. It would appear un- 

 necessary to add lime, when there is already a 

 small quantity in the marl, were it not that 

 there is still another substance mentioned as 

 occurring chiefly in the marl of the dividing 

 ridge and deep cut. This substance is the 

 sulphuret of iron, the presence of which is 

 shown by the large amount of white efflores- 

 cence with which it becomes coated after ex- 

 posure to the air, precisely similar to those pits 

 where it is observed in pieces of considerable 

 size. After the marl has been exposed to the 

 air for a short time, a whitish efflorescence 

 forms on its surface, which has a strong styp- 

 tic taste, and is the sulphate of iron, formed 

 from the sulphuret ; but the snow-white efflo- 

 rescence is chiefly sulphate of lime, or plaster. 

 Now, the latter marl contains 1 lime, and the 

 former does not; and hence this operation of 

 nature in the formation of plaster from sulphu- 

 ret of iron points out to us the manner of at- 

 taining the same result, viz., by mixing with 

 marl which exhibits an efflorescence after ex- 

 posure to the air, a quantity of lime sufficient 



