Vol. 8. 



ROCHESTER, . N. Y. — OCTOBER, 1847. 



No. 10. 



THE GENESEE FARMER : 



Issued the first of each mcnith, in Rochester, N. Y., by 



D. D. T. MOORE, PROPRIETOR. 



DANIEL LEE, EDITOR. 



P. BARRY, Conductor of the Horticultural Department. 



Study the Soil. — Magnesia. 



In former articles under the heading " Study 

 the Soil," we have noticed silica, (pure flint 

 sand,) alumina, iron, and lime. We now ask 

 attention to a ^ew remarks on the alkaline earth 

 called magnesia. 



This mineral is found in the ashes of all, or 

 nearly all, cultivated plants ; and exists in the 

 blood and lean meat of animals as well as in 

 their bones, in the form of a phosphate, but in 

 a much smaller quantity than phosphate of lime. 

 The magnesia found in soils is mostly derived 

 from a rock, technically called dolomite, which 

 is a magnesian limestone. Where the propor- ; 

 tion of magnesia is large, and the rock near the ' 

 surface, the soil is apt to be wet, and very sterile, j 

 This is particularly the case in some places in 

 England and Germany. The free use of burnt 

 lime has often proved injurious, from the cir- 

 cumstance of its containing more magnesia than 

 -can be safely applied to soils and crops at once. 

 All the salts of this mineral, unlike those of lime, 

 are extremely soluble, except the carbonate. — 

 It is in this form that all sedimentary magnesian 

 rocks are found. Rocks of an igneous origin, 

 i. e., those that have been melted in volcanic 

 iire, or something of the kind, which contain 

 magnesia, present it to the chemist, not in the 

 form of a carbonate, but a silicate of that base. 

 Serpentine and talc (minerals of a volcanic ori- 

 gin,) are nearly pure silicates of magnesia. In 

 hornblende and augite, (minerals of a plutonic 

 or granitic origin,) we find a considerable 

 amount of the same compound. 



The student (and are we not all students ?) 

 who desires to learn something more of agricul- 

 tural geology, will not take exceptions to the 



introduction of such terms as hornblende, augite, 

 serpentine, and talc, when he is informed that 

 it is from the slow decomposition of these crys- 

 talline rocks, througli the agency of carbonic 

 acid in the atmosphere, aided by frost, rain, and 

 electricity, that all stratified rocks of carbonate 

 of magnesia and of lime are produced. The sil- 

 icates of lime, potash, and soda, are decomposed 

 by the same atmospheric agents which decom- 

 pound the silicate of magnesia. Hence, almost 

 all limestone rocks contain more or less carbon- 

 ate of magnesia. Stratified sandstone is the sili- 

 ca with more impurities, separated from the 

 alkalies and alkaline bases in granitic rocks. 



Both Liebig and Boussingault suggest that 

 magnesia will perform the function of lime in 

 the economy of plants ; and hence, if a soil is 

 found to possess a fair supply of either alkaline 

 earth, the other need not be applied. With due 

 deference to these distinguished names, we must 

 say that this idea of the isomeric* character of 

 lime and magnesia in building up the organized 

 tissues of vegetables and animals, is not well 

 founded. Those excellent chemists have failed 

 duly to consider the important fact in animal 

 physiology, that the phosphate of magnesia never 

 serves as a substitute for bone earth. Hence, if 

 cultivated plants could grow and perfect their 

 seeds without lime, using magnesia in its stead, 

 all such plants and their seeds would be worse 

 than useless as food for man and his domestic 

 animals. The truth is that, Nature furnishes 

 and uses both phosphates, but more of the salt of 

 lime than of magnesia. 



When we study rocks, soils, and plants, with 

 reference to their agricultural value, we must 

 never omit to consider the various elementary 

 bodies which Providence has appointed to form 

 the whole system of a healthy liuman being. — 

 All authors with whom we are acquainted, that 

 have written on agricultural geology and chem- 

 isty, have failed in this respect. Dr. Sprengel, 

 whose analyses of plants are the frame work of 



* Isomeric. — In chemistry it is one substance that can ex- 

 astly fill the place and office of another. 



