Whan it was discovered that ammonia is derived from the atmosphere, and that it descends in rain, a new light was thrown upon the refreshing and invigorating effect of heavy showers, which act not merely by their water, as once was thought, but also by the carbonate of ammonia which they bring down. So far as agriculture is concerned, this is, however, a truth devoid of possible application, because the volatile carbonate cannot be advantageously used artificially through the agency of the atmosphere. But it is otherwise with gardeners, who have to create an artificial atmosphere in a confined space. It is not a little remarkable, then, that so simple an agent, so easily procured, and applicable with so little trouble, should scarcely ever have been employed in hothouses in the proper manner. Where it has been used, it has been almost invariably when dissolved in water and applied with a syringe. Professor Lindley at length gives the proper mode of application; doubtless many have thought of it, but the present will, we believe, be the first correct instructions on the subject in this country.

The carbonate of ammonia of the atmosphere is suspended, dissolved in invisible vapor. In this state it is incessantly in contact with every part of the foliage. When rain falls, the ammonia disappears for the moment, passing down in the rain drops to the ground, and thence arriving at the roots of plants. But if it is in gardens first dissolved in water, and then thrown upon plants with a syringe, natural conditions are by no means imitated. It reaches no part except that on which the water falls, half the upper surface and nearly all the under surface of the foliage is missed, and it is scarcely detained even upon the parts which the water actually touches. The proper course is to throw it into the air in the form of gas; this is easily effected in the following manner: -

When a greenhouse or hothouse is shut up, warm and damp, rub upon the heated pipes, the flues, or a hot piece of metal, a small piece of carbonate of ammonia with some water (not dry); the peculiar smell of smelling salts will be instantly perceived, and, if this is done at the two ends of a house, as well as in the middle, the air will rapidly receive a sufficient charge of the substance. After it has been allowed to remain about the plants for a short time, some gardeners would syringe their houses freely; but it is doubtful whether that is the best plan, provided the air of the house is naturally damp. The effect of this simple application is very remarkable, quickly producing a visible change for the better in the appearance of the plants.

But caution must be used in the application. A piece of carbonate of ammonia as large as a quarter of a dollar is sufficient for a charge in a stove 40 feet long; and it is indispensable that it should be volatilized by rubbing it in water, otherwise its causticity is too great, and leaves are burnt.