CALCAREOUS MANURES-THEORY. 



53 



The potash was first carefully taken out of all these samples. The re- 

 maining solid matter was silicious sand and charcoal ; the proportion of 

 the latter varying according to the degree of heat used in burning the wood, 

 wliich was not permitted to be very strong, for fear of converting the calca- 

 reous earth into quick-lime. 



It must be evident and unquestionable that all the carbonate of lime 

 yielded by the ashes had been necessarily furnished in some form by the 

 soil on which the plants grew ; and when the soil itself contained no carbo- 

 nate, as in all these cases, some other compound of lime must have been pre- 

 sent, to enable us to account for these certain and invariable results. The 

 presence of a combination of lime with some vegetable acid, and none other, 

 would serve to produce such effects. According to established chemical 

 laws, if any such combination had been taken up into the sap-vessels of 

 the tree, it would be decomposed by the heat necessary to convert the wood 

 to ashes ; the acid would be reduced to its elementary principles, and the 

 lime would immediately unite with the carbonic acid, (which is produced 

 abundantly by the process of combustion,) and thus present a product of 

 carbonate of lime newly formed from the materials of the other substances 

 decomposed.* 



On the foregoing facts and deductions, I am content to rest the truth of 

 the existence of acid and neutral soils. 



I have chosen to leave all the preceding part of this chapter (with the ex- 

 ception of a few merely verbal corrections and alterations) precisely as it 

 appeared in the first edition of this essay, (January 1832.)t But since that 

 time I have first heard of a discovery, and of consequent investigations by 

 men of science, which seem to furnish direct proof of what I have been 

 contending for, viz. : the existence of a vegetable acid substance in soils and 

 maiiures, generally diffused, and often in large proportions, and yet tvhich 

 had not been knotvn or suspected by chemists previously. The first intima- 

 tion of this discovery which reached me was in the ' Alphabet of Scientific 

 Gardening,'' by Professor Rennie, published in London in 1833, from which 

 the part relative to this subject will be quoted below. Since, I have 

 seen the French version of the late work of Berzelius, in which his 

 views of humic acid (or, as he names it, the geic acid.) are given more at 



* The reascniofi; on the presence of the carbonate of lime found in ashes, from acid 

 soils, does not appiy to the phosphate of hme which is also always present. The latter 

 salt is not decomposed by any known degree of heat, [Art. Chemistry, in Edin. Ency.'] 

 and therefore might possibly have remained unchanged, in passing from the soil to the 

 tree, and thence to the ashes. 



t The general position and views taken as to acid and neutral soils are also, in sub- 

 stance and purport, just as they appeared in my first publication on this subject in 1821. 



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