It is fortunate, however, that the best means to kill weed-seeds in the manure, are also the best for rendering the manure most efficient. I was talking to John Johnston on this subject a few days ago. He told me how he piled manure in his yards. “I commence,” he said, “where the heap is intended to be, and throw the manure on one side, until the bare ground is reached.” “What is the use of that?” I asked. “If you do not do so,” he replied, “there will be some portion of the manure under the heap that will be so compact that it will not ferment, and the weed-seeds will not be killed.” “You think,” said I, “that weed-seeds can be killed in this way?” “I know they can,” he replied, “but the heap must be carefully made, so that it will ferment evenly, and when the pile is turned, the bottom and sides should be thrown into the center of the heap.” LOSS OF AMMONIA BY FERMENTING MANURE. If you throw a quantity of fresh horse-manure into a loose heap, fermentation proceeds with great rapidity. Much heat is produced, and if the manure is under cover, or there is not rain enough to keep the heap moist, the manure will “fire-fang” and a large proportion of the carbonate of ammonia produced by the fermentation will escape into the atmosphere and be lost. As I have said before, we use our horse-manure for bedding the store and fattening pigs. We throw the manure every morning and evening, when the stable is cleaned out, into an empty stall near the door of the stable, and there it remains until wanted to bed the pigs. We find it is necessary to remove it frequently, especially in the summer, as fermentation soon sets in, and the escape of the ammonia is detected by its well known pungent smell. Throw this manure into the pig-cellar and let the pigs trample it down, and there is no longer any escape of ammonia. At any rate, I have never perceived any. Litmus paper will detect ammonia in an atmosphere containing only one seventy-five thousandth part of it; and, as Prof. S. W. Johnson once remarked, “It is certain that a healthy nose is not far inferior in delicacy to litmus paper.” I feel sure that no ammonia escapes from this horse-manure after it is trampled down by the pigs, although it contains an additional quantity of “potential ammonia” from the liquid and solid droppings of these animals. Water has a strong attraction for ammonia. One gallon of ice-cold water will absorb 1,150 gallons of ammonia. If the manure, therefore, is moderately moist, the ammonia is not likely to escape. Furthermore, as Dr. Vœlcker has shown us, during the fermentation of the manure in a heap, ulmic and humic, crenic and apocrenic acids are produced, and these unite with the ammonia and “fix” it--in other words, they change it from a volatile gas into a non-volatile salt.