CHEMICAL SCIENCE. 225 



in a juice distinctly acid. Most vegetable acids and dilute mineral 

 acids preserve it from change, but it is quickly turned brown by al- 

 kalies. M. Chatin was led to the discovery by observing that certain 

 tissues which are always colorless in a fresh plant are regularly col- 

 ored brown in old specimens ; and that tissues in process of forma- 

 tion, and those which take the most active part in the phenomena of 

 vegetation, show the coloration. He supposed, therefore, that the 

 nourishing juices of vegetables must contain a principle which is col- 

 orless in living tissues, but which, on the death of the organs, and 

 from other causes, undergoes a change indicated by the alteration 

 of the color, and is the exclusive cause of the brown appearance of 

 autumnal and dead leaves in general. A, after it has turned brown, 

 may be extracted from autumn leaves by treating them with a mix- 

 ture of ether and water, the former of which will dissolve the green 

 matter and the latter the brown, but the author does not tell us how 

 we may separate the original colorless A. 



AGKICULTURAL EMPLOYMENT OF NODULES OF PHOSPHATE 



OF LIME. 



In the opinion of M. Boblique, the inefficacy of native calcareous 

 phosphates can, in numerous instances, be traced to two principal 

 causes : 



1. To the great cohesion of this substance, which renders assimila- 

 tion very difficult when it is determined only by natural agents. An 

 attempt has been made to remedy this disadvantage by treating the 

 nodules with powerful mineral acids, but this is a costly method, and 

 might perhaps prove injurious to those lands which do not contain a 

 sufficient quantity of bases in a condition to saturate the excess of 

 acid employed to effect the solution of the calcareous phosphate. 



2. To the absence of soluble silica. Now, silica is as indispensa- 

 ble to cereals as phosphoric acid ; it forms their skeleton, and to its 

 absence is justly attributed the contingency called " versement." If 

 the soil contains an insufficient quantity of assimilable silica, the stalk 

 does not acquire the properties necessary for a good harvest, and the 

 phosphates added to the soil, under these circumstances, are useless. 

 These considerations have guided me in devising some means to 

 insure the useful employment of the nodules. 



Pulverized nodules are mixed with fifty per cent, of their weight 

 of sea salt. This mixture is exposed, in a furnace or cylinder, in a 

 current of steam, to a temperature a little below redness. 



If, as is sometimes the case, the nodules do not contain a suffi- 

 ciency of silica, the deficiency must be made up previous to the opera- 

 tion. The reaction of silica on chloride of sodium in contact with 

 the vapor of water is well known, resulting in the formation of sili- 

 cate of soda and hydrochloric acid. In this special case the latter 

 acts on the phosphate of lime, from which it takes two equivalents of 

 lime, and gives rise to chloride of calcium and biphosphate of lime. 

 However, all the phosphoric acid does not combine with the lime ; it 

 sometimes forms a considerable quantity of phosphate of soda. It is 

 thought that this latter product is chiefly owing to the decomposition 

 of phosphate of iron. All this metal, in fact, is found in the state of 



