28 LESSONS ON CHEMISTRY. 



therefore, when the farmer perceives its penetrating odour 

 near the manure-heap, or where guano has been stored, he 

 may be certain that it is escaping into the atmosphere, and 

 that, if neglected, these manures will gradually be rendered 

 less capable of benefiting his fields. Chemistry teaches us 

 how by very simple means, as will be hereafter described, 

 this loss of ammonia may be prevented.* 



19. Though Saussure, whose works contributed to direct 

 the attention of philosophers to the substances which serve 

 for the food of plants, suspected the presence of this gas in 

 the atmosphere, it was reserved for that great chemist, whose 

 writings may be said to have originated the modern theory 

 of agriculture, to demonstrate its existence by experiment. 

 Liebig, with his usual sagacity, reasoned that the difficulty 

 of detecting the presence of ammonia must arise from the 

 extremely minute portion of it which existed in the few 

 cubic inches of air usually submitted to examination, and 

 that we would more easily convince ourselves of its presence 

 by operating upon some pounds of rain water; by which 

 means we should obtain in solution, carried down with the 

 rain, the whole amount of it diffused through several cubic 

 feet of air. Accordingly, he collected rain water in the 

 neighbourhood of Giessen, where he resides, when the wind 

 was blowing in the dkection of the town, so that the rain 

 could not obtain any ammonia from the smoke, &c. Several 

 hundred pounds of this water were boiled to dryness in a 



* Ammonia is most conveniently prepared by introducing into a 

 flask a mixture of one part of sal-ammoniac and two parts of quick- 

 lime, and applying a gentle heat. The substances must, previously to 

 being mixed, be reduced separately to a fine powder. As ammonia is 

 very soluble in water, it cannot be collected over the water trough, but 

 bottles and tubes may be filled with it by fixing, by means of a cork, 

 to the mouth' of the flask, a tube of glass of sufficient length to 

 pass to the bottom of the vessel used to receive the gas. 

 When inverted over the tube (^Fig. 4) the light gas will 

 entirely expel the atmospheric air from the receiver. If 

 you close the receiver and bring it over a vessel contain- 

 ing water, and withdraw the cork, the water will rush 

 up with force, and unite with the gas. This experiment, 

 when a large bottle of gas is used, and the water is 

 mixed with some blue vegetable colour reddened by the 

 addition of a few drops of vinegar, is exceedingly striking. 

 The water rushes into the bottle, and its blue colour is 

 restored by the alkaline gas. Water saturated with this 

 gas is what is sold as liquid ammonia. Fig, 4. 



