300 CHEMICAL COMBINATIONS 



ties, possessed exclusively by stable manure, for we know, also, 

 that by placing living plants in a hot-bed, newly made, even if 

 the heat of the bed be kept from injuring the roots, they will 

 soon cease to exist as living beings, purely from an excess of 

 those very gases which, in proper proportions, add so much to 

 their natural luxuriance. Plants are more sensitive, and more 

 easily affected, with regard to life and health, than many living 

 animals. Many persons, who have paid little attention to veg- 

 etable physiology, may be dubious of this fact, but it is, neverthe- 

 less, true. The atmosphere of a hot-house may be impregnated 

 with ammoniacal and other gases, beneficial to vegetable life, 

 without being offensive to the ordinary visitor, or even detected 

 by him in the atmosphere of the house. Besides, it is so quick- 

 ly absorbed by the plants, that it has to be saturated almost to 

 excess before much smell is sensibly felt. We have carried on 

 the practice daily, of impregnating the atmosphere of a green- 

 house with carbonate of ammonia, by dissolving it in water and 

 sprinkling through the house, without the ammonia being de- 

 tected, except by the acute olfactory organs of the experienced 

 chemist, except, perhaps, when the atmosphere was impregnated 

 to an excess, which, by way of experiment, was sometimeF the 

 case. 



4. This subject now resolves itself into the following consid- 

 erations : 



(1.) Which gases is it necessary to generate artificially, for 

 the purpose of increasing the capacity of the atmosphere of a 

 hot-house to sustain vegetable life in a state of vigor and health- 

 fulness ? 



(2.) How are we to determine the precise proportions of each, 

 so that we may keep as near as possible to that point of health- 

 fulness, which lies midway between deficiency and excess ? 



In replying to the first question, it is not necessary to enter 

 into an elaborate detail of the various volatile gases which 

 arise from the combination of the prime elements of the organic 

 world, in different proportions, and which are absorbed by plants. 

 It may be sufficient for my present purpose, to notice that grand 

 stimulus of vegetation already alluded to, viz., ammonia, which, 



