Bibliography. 195 



We have made these exceptions to Dr. Dana's rules, not with a view 

 to prove them entirely erroneous, but to suggest to the author, whether 

 in another edition, they may not be so modified as to obviate all objec- 

 tions. Even in their present state, we regard them as nearer the truth 

 than the notions that widely prevail. But we think they can be improved. 



The fifth principle of agricultural chemistry asserts, that " all soil 

 contains sulphate and phosphate of lime.'''' For the discovery of this im- 

 portant principle, agricultural chemistry is indebted to Dr. Dana. It 

 was first announced in the Report on the Economical Geology of Mas- 

 sachusetts, written in 1837 and published in 1838, and is there accom- 

 panied by what Dr. Dana calls the " agricultural proof;" that is, the evi- 

 dence derived from the composition of plants. This evidence was abun- 

 dantly confirmed by the analysis of no less than one hundred and forty 

 six soils from every variety of formation in Massachusetts. In all 

 these soils, (except one, which was entirely made up of pure limpid 

 quartz in the form of sand,) sulphate and phosphate of lime were found. 

 (See final Report on the Geology of Massachusetts, Vol. I, p- 41.) The 

 difficulty of detecting the phosphates had produced the belief that they 

 exist only in a few soils. But the admirable rules given by Dr. Dana 

 on this point, enable any chemist to satisfy himself that almost every 

 plant-bearing soil contains phosphates, usually less than one per cent. 

 In Liebig's Organic Chemistry of Agriculture, &c. published in 1840, 

 this same principle, so far as phosphoric acid is concerned, is advan- 

 ced ; but whether the result of his own discoveries or of a knowledge 

 of Dr. Dana's announcement, nearly three years earlier, does not ap- 

 pear. 



The sixth principle is, that " soil, consisting chiefiy of one silicate, 

 or salt, is always harren. 



The seventh principle is, that " one base may he substituted for an- 

 other in an isomorphous proportion.'''' These " isomorphous substitu- 

 tions in plants relate only to the vegetable or organic acids ;" yet the 

 principle holds true in respect to the inorganic parts of soils, and admits 

 of several important applications made with great ingenuity by the au- 

 thor. But our limits compel us to pass them unnoticed. 



The eighth principle is, that " geine in some form is essential to ag- 

 riculture.'''' As discussions perplexing to the farmer have arisen in 

 our country respecting geine. Dr. Dana has thought it necessary to 

 be very explicit as to the sense in which he uses the term ; and he 

 has added an appendix to the chapter on this subject, detailing its his- 

 tory. He uses the term in two senses, viz. an agricultural sense and a 

 chemical sense. 



" In all its forms," he says, " it is agriculturally one and the same 

 thing. They are all included in the terms humus, or mould, or geine. 



