82 LIME IN WOOD ASHES. 



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 carbonate, as in all these cases, some other 

 compound of lime must have been present, to enable us to account 

 for these certain and invariable results. The presence of a com- 

 bination 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 decom- 

 posed.* 



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

 truth of the existence of acid and neutral soils. 



NOTE. 



Scientific Confirmation of the doctrine of Acid in Soils. 



[1835. I have chosen to leave all the preceding part of this 

 chapter (with the exception of a few merely verbal corrections and 

 alterations) precisely as it appeared in the previous edition of this 



conclusions. He adds the following words, .which, in connexion with his 

 context, show that his opinion concurs with my position, that (supposing 

 enough lime to be present) the proportion in the ashes of plants is accord- 

 ing to the nature and demand for lime, of the particular plant; and not to 

 the great abundance or scarcity of lime in the soil producing the plant. 

 He says "the ash of the same plant, if ripe and healthy, is nearly the 

 same in kind and quality in whatever circumstances (if favourable) of soil 

 or climate it may grow." (p. 244.) That chemists now generally admit 

 De Saussure's conclusions to be erroneous may also be safely inferred 

 from this : the many results of the ashes of plants Avhich have appeared 

 in recent works, are rarely (if ever) accompanied by any report of the 

 contents of the soil whence derived; thus showing that the calcareous or 

 other ingredients are inferred to be according to the kind of plant, and 

 not dependent on the character of the soil. 1849,] 



* The reasoning on the presence of the carbonate of lime found in 

 ashes from acid soils, does not apply to the phosphate of lime 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 Lave 

 remained unchanged, in passing from the soil to the tree, and thence to the 

 ashes. 



