“It is a term,” said the Doctor, “we used to hear much more frequently than we do now. Ammonia is composed of 14 lbs. of nitrogen and 3 lbs. of hydrogen; and if, on analysis, a guano or other manure was found to contain, in whatever form, 7 per cent of nitrogen, the chemist reported that he found in it 8½ per cent of ‘potential’ ammonia. Dried blood contains no ammonia, but if it contained 14 per cent of nitrogen, the chemist would be justified in saying it contained 17 per cent of potential ammonia, from the fact that the dried blood, by fermentation, is capable of yielding this amount of ammonia. We say a ton of common horse-manure contains 10 or 12 lbs. of potential ammonia. If perfectly fresh, it may not contain a particle of ammonia; but it contains nitrogen enough to produce, by fermentation, 10 or 12 lbs. of ammonia. And when it is said that dry swamp-muck contains, on the average, 2.07 per cent of potential ammonia, it simply means that it contains nitrogen enough to produce this amount of ammonia. In point of fact, I suppose muck, when dug fresh from the swamp, contains no ammonia. Ammonia is quite soluble in water, and if there was any ammonia in the swamp-muck, it would soon be washed out. The nitrogen, or ‘potential ammonia,’ in the muck exists in an inert, insoluble form, and before the muck will yield up this nitrogen to plants, it is necessary, in some way, to ferment or decompose it. But this is a point we will discuss at a future meeting.” CHAPTER VII. TILLAGE IS MANURE. The Doctor has been invited to deliver a lecture on manure before our local Farmers’ Club. “The etymological meaning of the word manure,” he said, “is _hand labor_, from _main_, hand, and _ouvrer_, to work. To manure the land originally meant to cultivate it, to hoe, to dig, to plow, to harrow, or stir it in any way so as to expose its particles to the oxygen of the atmosphere, and thus render its latent elements assimilable by plants. “When our first parent,” he continued, “was sent forth from the Garden of Eden to till the ground from whence he was taken, he probably did not know that the means necessary to kill the thorns and thistles enhanced the productiveness of the soil, yet such was undoubtedly the case.