120 Observations on Liebig's " Organic Chemistry." 



and take the brown-coloured liquid in barrels to the field, in 

 preference to manure. Dr. Thomson says tlie humate of potash 

 is brown-coloured also and soluble, perhaps this may be formed 

 in the dung: but, from the aptitude of humic acid to be dis- 

 placed by other acids, I am afraid the carbonic acid may take 

 its place, as it will likely be most plentiful. It appears, also, to 

 be little more soluble than the acid itself (see quotation from 

 Sprengel, p. 8.). I think it most probable that the benefits of 

 manure are more likely to arise from the neutral soluble salts of 

 carbonic acid, as ammonia, potash, soda, &.c. ; the other salts 

 of ammonia, phosphates, &c. ; and the carbonic acid itself in 

 solution, likely saturation, in the water of the manure; as also 

 the other soluble vegetable and animal substances in the heap ; 

 than from the small quantity of humic acid found in the water, 

 2J00 pai't. Dr. Liebig had before stated (p. 25.) that these 

 soluble vegetable matters could not be assimilated though 

 absorbed; but he states in p. 124, 125. the great quantities of 

 starch deposited in pine trees, and sugar in maple trees, also 

 the starch deposited in potatoes ; there are also large deposits 

 of mucilage and albumen. When he considers all these as 

 reduced into gum or mucilage next year, to be assimilated in 

 the young shoots, I cannot see, if the plant can assimilate 

 these, that it will not assimilate also the same substances in solu- 

 tion in the manure, and absorbed by the roots, as Sir Humphry 

 Davy's experiments would lead us to believe. It appears the 

 statements in p. 25. are advanced as the opinions of others 

 more than his own. 



He here gives us some elaborate dissertations on the way 

 in which these substances are assimilated, and points out the 

 necessity of nitrogen in forming the principle called diastase, 

 which greatly assists in reducing the starch to gum. The 

 nitrogen absorbed by the roots of plants, in the gluten and 

 albumen of the soluble substances, produces the nitrogen for 

 forming diastase ; it is found surrounding all the organs, and 

 hence the great necessity of nitrogen to carry on the assimi- 

 lation of the food. Unless nitrogen be present, he says, the 

 food will not be assimilated ; and people who live on potatoes 

 have more granules of undecomposed starch in their excre- 

 ment. If there is a deficiency of nitrogen in animals, fat 

 is formed ; if in plants, oils, resins, starch, &c. ; or these or 

 the food are returned as excrement : the nitrogen itself, if in 

 excess, will also be returned as excrement. The gluten, albu- 

 men, and mucilage, he says, contain nitrogen ; the sugar, starch, 

 oil, wax, and resins do not ; and potatoes or beet have less 

 starch and sugar when animal manures abound in the soil, 

 though the plants are larger. As mucilage is first formed in the 

 potato, which is afterwards ripened into starch, it is probable 



