48 LESSONS IN CHEMISTRY. 



other useful contrivances for producing instantaneous light, it 

 is everywhere to be found ; and, in London alone, it is stated, 

 that so much as 200,000 lbs. of it are annually consumed. 

 When a piece of phosphorus is set on fire it unites with 

 the oxygen of the air, and produces a white, solid, and 

 strongly acid compound, which is 'phosphoric acid. This 

 acid enters into the composition of all our cultivated plants, 

 and united with lime produces a compound named phosphate 

 of lime, which forms the chief part of bones, and also exists 

 in considerable quantity in the milk of animals.* 



54. Such is a plain account of the substances which the 

 ashes of your crops invariably contain. In the infancy of agri- 

 cultural science it was imagined that these earthy matters 

 exercised no influence upon the plants of which they had 

 formed a part — that they were only accidentally present. 

 But as chemistry advanced and examinations of the ashes of 

 plants became more numerous and accurate, it was ascer- 

 tained, beyond all question, that these substances were most 

 important — nay, indispensable to the existence of the vege- 

 table kingdom, and that without their presence in the plant, 

 even could it grow, it would be without value and incapable 

 of serving us for food. 



55. Within the last few years repeated examinations of 

 both wild and cultivated plants have been made by chemists 

 in this country and on the Continent, and it has been clearly 

 shown, by careful experiment, that for a pknt to come to 

 perfection, or to form its seed, the soil in which it is placed 

 must contain the materials which we have just described, as 

 entering into the composition of the incombustible ash of 

 vegetables. But the discovery that every plant which springs 

 up along the roadside, or is carefully tended in the farm, 

 requires a certain amount of mineral matters for its develop- 

 ment, is not the only useful intelligence which science has 

 derived from this inquiry, or which it can afford to the 

 farmer. It has, in addition, given to us a piece of informa- 

 tion which is destined to exercise the gi-eatest mfluence upon 



* In the ashes of sea plants two elementary bodies are discovered 

 which do not exist in the crops of the farmer. These are termed iodine 

 and bromine. Iodine is a metallic looking substance, something like 

 black lead in appearance ; it is procured from kelp, and is at present 

 very extensively employed in medicine. Bromine is a reddish brown 

 liquid with a peculiar disagreeable pungent smell, which, when inhaled, 

 excites \^olent irritation of the nostrils. It bleaches vegetable colours 

 like chlorine. 



