244 FERTILIZERS. 



Gypsum is found in the ash of plants ; this fact supports the view of Davy. Gypsum absorbs 

 ammonia, and when this takes place, as it will to a certain extent in growing plants, it will fix 

 and furnish ammonia to the plant ; and this favors Liebu:'s views, and they are certainly ra- 

 tional. So plants possess the power of decomposing the salts received into their tissues, and 

 there is very little reason for doubting the effect of clover, and sanfoin, on the sulphuric acid of the 

 sulphates ; that they do separate from the oxygen and combine it with another element, in some 

 way not well understood ; and hence Boussingault's view also is, or may be true. At any 

 rate the three theories are partial and do not cover the whole ground ; all are defective for want 

 of fullness, and hence only partially true, and true only as far as they go ; neither of them is 

 false. Boussingault takes a very rational view of the favorable effects of gypsum : he re- 

 gards its sparing solubility as an important feature in explaining its effects. A gallon of water 

 dissolves about a quarter of an ounce of the sulphate. Now plants require, and indeed take 

 up with reluctance only small doses of mineral salts, and their capacity for taking up and ap- 

 propriating them is necessarily limited ; hence the economy of plaster, as on'j a small quantity 

 is dissolved at one time — just that proportion which the constitution of liie plant demands ; 

 hence, too, its value is prolonged, and its good effects visible for several seasons in succession. 

 Phosphate of lime. The constitutions of animal bodies require this salt: it ix'sts in the 

 blood, in muscle, in albumen, casein and most of the fluids, milk, cream, etc. Its importance 

 to the animal, and indeed to all organized bodies, has been dwelt upon sufficiently already. 

 The composition of the bodies just mentioned, is given in the second volume. Phosphorus as a 

 simple undecompounded body, does not exist in nature ; its properties forbid this : hence it is al- 

 ways found in combination with other substances, lime, iron and alumine, and in the tissues of 

 vegetables and animals, with soda, potash and magnesia. The most abundant salt of phospho- 

 rus is phosphate of lime ; it is a native mineral, and found in New-York imbedded in crystals, 

 in a peculiar limestone, denominated primary limestone in my Report of the Geology of the 

 Second District. The crystals are six-sided, usually green and greenish white : the largest 

 which has ever been seen is twelve inches long, and weighs nineteen pounds. Phosphate of 

 lime is also associated with magnetic oxide of iron ; a fact which I first made known in the 

 volume just referred to. It was, however, known to occur associated with some of the ores of 

 iron, but had not been recognized in distinct crystalline masses of a large size. Another form 

 of this mineral is that which was also described under Eupyrchroite : it is in mamillary masses 

 of a dark green color, annexed to a trap dyke, resembling the ordinary dykes of greenstone. 

 This association is an important fact, and taken with other facts, its association with primary 

 limestone and lava, and iron ore, point to an igneous origin. Igneous rock, too, as has been 

 proved by Fownes, in his well known prize essay, is contained in the decomposing granites, 

 porphyry, trachyte, etc. It is, therefore, highly probable that a supply of this substance is to 

 be sought for in the igneous rocks. The basis of the globe furnishes this substance to the soil ; 

 it finds its way to the sea, and is there a food for fish. The trap dyke, in connection with 

 the Eupyrchroite, contains, as I have satisfied myself by Berzelius's test, phosphoric acid, 

 probably in combination with iron, alumina and lime. This fact is mentioned for the purpose 



