Observations on Liebig^s " Organic Chemistry.^' 101 



from them, and the bases of potash, &c., returned to the earth, 

 to be again neutralised and taken up, which does not seem at all 

 improbable ; we may thus greatly augqient the quantity of carbon 

 absorbed by the roots. 



Besides, it does not appear how we should be solely con- 

 fined to the action of humic acid, for the production of carbon. 

 Dr. Thomson, who gave it the name of ulmic acid, having 

 extracted it from exudations of the elm, says that moss water 

 is composed of humic acid and water ; and yet we have never 

 heard of any great results from moss water. The same authority 

 states that the experiments of Mr. Cavendish proved that water 

 is capable of absorbing 107 volumes of carbonic acid gas, to 

 every 100 volumes of water, at the ordinary pressure of the air ; 

 and the capability is increased very much when further pressure 

 takes place. All water running in the earth contains it; it is the 

 carbonic acid which bubbles, and gives the brisk flavour to spring 

 water. I cannot, therefore, see what is the cause that would 

 prevent water saturated with this gas, as it will be in manure, and 

 containing it in large quantity as in rain water, from being ab- 

 sorbed directly by the spongioles of the root. Experiments have 

 been thought to be against this ; but the same experiments would 

 be against the absorption by the leaves, as the leaves were 

 sprinkled with water containing carbonic acid, in those experi- 

 ments, as well as the roots. Dr. Liebig thinks the error was 

 owing to the unnatural circumstances in which the plants were 

 placed, which, I believe, is the truth. The experiments of Sir 

 Humphry Davy and others show that the leaves of growing 

 plants purify air containing carbonic acid, and consequently 

 must have absorbed it. Other experiments, also, of the same 

 philosopher show that, when the beak of a retort containing 

 carbonic acid was introduced amongst the roots of growing grass 

 in the soil, there was an evident and great improvement in the 

 growth of that particular spot in a few days ; proving that the 

 gas had been absorbed by the roots. Plants of mint, also, the 

 roots of which he had introduced into water containing charcoal, 

 grew very rapidly ; and though no solid charcoal, the test for 

 which the experiment was instituted, was found in the vessels of 

 the plant, yet undoubtedly carbonic acid must have been the cause 

 of the growth being more than usual ; the charcoal would give 

 out nothing but carbonic acid, and perhaps a little potash. I 

 have myself often tried the effect of charcoal from wood in 

 hyacinth glasses, and always found the plants more luxuriant 

 than those which got none. I think whoever will be at the trouble 

 of reading the appendix to Dr. Liebig's work, on the experi- 

 ments extracted from Buchner's Repertorium, showing the im- 

 mense effects produced bj'^ growing plants wholly in charcoal 

 with plenty of water, will not fail to be convinced, that the 



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