THE POLYTECHNIC REVIEW AND MAGAZINE OF Science, Literature, and the Fine Arts. EDITED BY GEORGE G. SIGMOND, M.D., ETC., ETC. AND BY THOMAS STONE, M.D., ETC., ETC. JULY-DECEMBER, 1844. LONDON: JOHN MORTIMER, ADELAIDE STREET, TRAFALGAR SQUARE. MDCCCXLIV. THE POLYTECHNIC REVIEW AND MAGAZINE. AGRICULTURAL CHEMISTRY. ON THE IMPORTANCE OF AGRICULTURAL CHEMISTRY TO PRACTICAL FARMERS, WITH A HISTORICAL SKETCH OF ITS RISE AND PROGRESS, AND THE MODE IN WHICH IT MAY BE STUDIED. In walking over a meadow where both cows and horses have pastured, the very striking difference produced on the grass by the droppings of each is apparent to the most careless observer. Around the horse droppings the herbage is usually yellowish, or parched, similar to the tufts of grass on gravel walks which have been purposely sprinkled with boiling water, in order to kill them. It seems therefore but fair to infer, that the horse droppings have diffused into the soil around them something which has a similar effect to boiling water in discolouring the grass. Around the droppings of the cows, on the other hand, the grass is more luxuriant, and of a finer green than in any other part of the field; similar to the irregular green rings of fine grass which may be seen in lanes encircling the spots where a party of Gypsies have had a fire. In this case, also, it would at first sight seem fair to infer, that the greater luxuriance of the herbage around the cows' droppings and the Gypsies' fireplace might arise from a similar cause, as the effects seem so similar; and so it has been and is thought by many observers, and so it is set down in some books on tillage. Yet, plausible as the view seems, that the increased luxuriance is owing to an increased supply of food,-in the one case to the manure of cow-dung, and in the other to the manure of ashes or charcoal,-closer investigation proves the inference to be far from correct, and might (although it did not) have led to the discovery of one of the leading and incontrovertible principles upon which the science of agriculture rests. Reverting to the fact of the horse droppings discolouring the grass, inasmuch as the effect takes place to some distance, it must either be caused by the diffusion of some liquid, some VOL. I.-N. S. B |