GASES. 



GASES. 



made to vegetate in the dark, they contained 

 much less oil than those vegetating in the 

 light, their resinous matter being then as 2 to 

 54 compared with those vegetating in the light. 

 They had even less earthy matters by one half; 

 but then they had exactly double the quan- 

 tity of water that the light-growing plants pos- 

 sessed. 



Snch, then, are the results of the free access 

 of the carbonic acid gas of the atmosphere to 

 the leaves of plants, it promotes their growth, 

 increases their vigour, and enriches their se- 

 cretions. The application of the same gas to 

 their roots, although it has not been examined 

 with the same care as its action upon their 

 leaves, is yet evidently attended with the high- 

 est advantage. Thus, this gas is one of the 

 constant products of putrefaction, wherever 

 this is going on; as over stagnant drains, 

 dung-heaps, and other putrefying matters: 

 then- vegetation is sure to be rankly luxuriant, 

 and that, too, in situations where the roots of 

 the plants are far removed from immediate 

 contact with the decomposing organic matters. 

 This may be easily shown by the repetition of 

 a very simple experiment, which was first made 

 by Davy. This great chemist filled a glass re- 

 tort, capable of containing three pints, with the 

 hot, fermenting dung and litter of cattle, and 

 examined the elastic fluids which were gene- 

 rated. In 35 cubic inches which were thus pro- 

 duced in 3 days, he found 21 of carbonic acid 

 gas, the remainder being chiefly nitrogen ; and 

 after thus ascertaining the composition of these 

 gases, he introduced the beak of another re- 

 tort, filled in a similar manner, in the soil un- 

 der the roots of some grass growing in the 

 border of a garden. In less than a week, a 

 very remarkable effect was produced on the 

 grass exposed to the action of these gaseous 

 matters of putrefaction ; their colour became 

 deeper, and their growth was much more luxu- 

 riant than the grass in any other part of the 

 garden. And hence, too, is derived one of the 

 chief advantages of applying organic matters 

 to the soil, and that in as immediate contact 

 with the crop as possible, just as is effected 

 when manures are added to the soil by the 

 drill ; for the roots or leaves of the plants are, 

 by the adoption of this plan, immediately in 

 contact with the evolved carbonic acid, and 

 other gases of putrefaction ; they are thus rea- 

 dily absorbed as they are generated, and no- 

 thing is lost by escaping into the atmosphere. 

 The gas, in fact, is instantly yet gradually 

 transmuted from the putrefying products of the 

 farm-yard into the flour of the wheat or the 

 nutritive matters of the grasses. And there is 

 yet another chemical reason why the manure- 

 drill or any other machine should be adopted 

 by the farmer to bring, as closely as possible, 

 every plant into immediate contact with the 

 decomposing manure he applies to his soil ; 

 and that is, the superior readiness with which, 

 in all cases of decomposition, the disengaged 

 substance enters into new combinations at the 

 very instant of its disengagement than it does 

 after it has been completely formed. Thus, to 

 give an instance, during the putrefactive fer- 

 mentation of vegetable substance, a quantity 

 of nitrogen is disengaged; and if this takes 

 522 



place under certain favourable circumstances 

 such as the presence of calcareous matters, 

 potash, and a dry, warm temperature at the 

 moment it is formedthe nitrogen combines 

 with oxygen, forms nitric acid, which unites 

 with the potash, and thus nitrate of potash, or 

 saltpetre, is formed ; but if the nitrogen is once 

 fairly disengaged, almost every endeavour of 

 the chemist has failed in making it unite with 

 oxygen so as to form the acid of saltpetre. 



In every way, therefore, in which the ques- 

 tion of applying manures in immediate contact 

 with the roots of plants can be viewed, the 

 more advisable does the adoption of the prac- 

 tice appear. 



The important services of the carbonic acid 

 gas of the atmosphere to vegetation have been 

 illustrated in various ways by more than one 

 able chemist. That given by Professor J. F. 

 Johnston, in his able Lectures on Agricultural 

 Chemistry, p. 218, is perhaps the most recent 

 and the most practical. He observes, "If we 

 were to examine the soil of a field on which 

 we are about to raise a crop of corn, and should 

 find it to contain a certain per centage, say 10 

 per cent, of vegetable matter (or 5 per cent, of 

 carbon), and after the crop is raised and reaped 

 should, on a second examination, find it to con- 

 tain exactly the same weight of carbon as be- 

 fore, we could not resist the conviction that, 

 with the exception of what was originally in 

 the seed, the plant, during its growth, had 

 drawn from the air all the carbon it contained. 

 The soil having lost none, the air must have 

 yielded the whole supply. Such was the prin- 

 ciple on which Boussingault's experiments 

 were conducted. He determined the per cent- 

 age of carbon in the soil before the experiment 

 was begun ; the weight added in the form of 

 manure ; the quantity contained in the series 

 of crops raised during an entire rotation or 

 course of cropping, until, in the mode of cul- 

 ture adopted, it was usual to add manure again ; 

 and, lastly, the proportion of carbon remaining 

 in the soil. By this method he obtained the 

 following results, in pounds per English acre: 

 From a course of, 1. Potatoes or red beet, 

 with manure; 2. Wheat; 3. Clover; 4. Wheat; 

 5. Oats. Carbon in the manure, &c., 2513 Ibs.; 

 carbon in the crops, 7544 Ibs. ; difference, or 

 carbon derived from the air, 5031 Ibs." 



The result of this course indicates that the 

 land, remaining in equal condition at the end 

 of the four years as it was at the beginning, 

 the crops collected during these years contain- 

 ed three times the quantity of carbon present 

 in the manure, and therefore the plants, during 

 their growth, must, on the whole, have derived 

 two-thirds of their carbon from the air. 



Oxygen. Oxygen gas, or vital air, which con- 

 stitutes 21 per cent, of the bulk of the air we 

 breathe, is absolutely essential to the growth 

 of plants. If this is withdrawn from the atmo- 

 sphere, they will no longer vegetate, their 

 leaves can no longer perform their functions. 

 But this use of oxygen by the leaves of vege- 

 tables is confined to the night ; it is only in the 

 dark that they absorb it. During this absorp- 

 tion the leaves of some plants, such as the 

 Cactus opuntia, and the houseleek (Sempervivum 

 tectorum}, do not emit any portion of carbonic 



