Observations 071 IJebig's '^ Orgcmic Chemistry y 145 



they run far through clayey or mossy soil, contain a great deal, 

 as may be seen from the colour of the water; and the scour- 

 ings of such ditches are very improper in composts for fine 

 flowers. Coal tar. Sir Humphry Davy says, contains a good 

 deal of carbonate and acetate of ammonia, and should be useful. 

 Soot, he says, likewise contains a good deal of carbonate of am- 

 monia, also an empyreumatic oil. The carbon of the coal is also 

 in a state of flocculent powder, fitted for absorption and decom- 

 position ; and the good effects of strewing it on soil in wet 

 weather, when it may be washed into the ground and yield both 

 carbon and ammonia, are well known. The quantity of car- 

 bonate of ammonia in any of these substances may be guessed 

 at by the pungency of the smell given off, when diluted in 

 water, and mixed with quicklime. 



I have now gone through the most of the substances used 

 as manures, and given the different views that may be taken of 

 their action, as far as in my power. It should be recollected, 

 also, that all bulk is not produce in the sense of food, much of it 

 is water; but it is not always even weight, and excitement may 

 expand the tissue without a corresponding deposit of food being 

 made in the tissue. From the extensive views of the professor 

 on the subject of nitrogen, it would seem of immense use, both 

 in stimulating and assisting the actions of vitality and chemical 

 force ; and is also, when assimilated, a great cause of the nu- 

 tritive condition of the food that plants yield to animals. 



The whole of Part I., the practical part of the work before 

 us, has now been considered. I have given, as well as in my 

 power in a single essay, a condensed view of the professor's 

 opinions ; every page, however, contains a mass of information 

 and reasoning which cannot be comprised in so small a compass ; 

 and I would earnestly advise all practical men, and all interested 

 in cultivation, to have recourse to the book itself and think for 

 themselves. The subject is vastly important, and we cannot esti- 

 mate how nuich may be added to the produce of our fields by 

 proceeding on correct principles. Though the information to be 

 got from the work is immense, yet I think practice would have 

 enabled the professor to modify many of the inferences deduced 

 therefrom ; and, while giving a condensed view of his opinions, 

 I have throughout interspersed remarks of my own. I have 

 brought practice to bear on theory as well as I could ; and 

 wherever my practical brethren differ from me, I hope they 

 will come freely forward ; it is the collision of opinions only 

 that can enable us to arrive at the truth. We should divest 

 ourselves of prejudice, and sift our own opinions as well as those 

 of others, or we will be apt to endeavour to make facts bend to 

 preconceived theories, to the prejudice of truth. We should not 

 give up the point till convinced, but we should not laise obstacles 

 1841. — III. SdSer. l 



