CHLORIDE AND MURIATIC ACID. 183 



capable of entering plants by iheir leaves or otber superior parts. They 

 must all, therefore, enter by the roots of plants, — must consequently ex- 

 ist in the land, — and must all be necessary constituents of that soil in 

 which the plants that contain them grow. 



It will not be necessary, therefore, to consider so much the relative 

 proportions in which these elementary bodies themselves exist in plants, 

 as that of the several chemical compounds which they form with oxy- 

 gen, or with one another — in which states of combination they exist in 

 the soil, and are found in the circulation and substance of the plant. As 

 a preliminary to this inquiry, however, it will be proper to lay before 

 you a brief outline of the nature and properties of these compound 

 bodies themselves — and of the direct injfluence they have been found to 

 exercise upon vegetable life. 



§ 4. Of those compounds of the inorganic elements which enter directly into 

 the circulation, or exist in the substance and ash of plants. 



I CHLORINE AND MURIATIC ACID. 



Chlorine. — If a mixture of common salt and black oxide of manga- 

 nese [sold by tliis name in the shops] be put into a flask or bottle of 

 colourless glass, and sulphuric acid (oil of vitriol) be poured upon it, a 

 gas of a greenish-yellow colour will be given ofT, and will gradually fill 

 the bottle. This gas is distinguished by the name o^ chlorine. 



It is readily distinguislied from all other substances by its greenish- 

 yellow colour, and its pungent disagreeable smell. It extinguishes a 

 lighted taper, but phosphorus, gold leaf, metallic potassium and sodium, 

 and many other metals, take fire in it and burn of their own accord. It 

 is nearly 4i times heavier than common air, and therefore may be 

 readily poured from one vessel to another. Water absorbs twice its 

 own bulk of the gas, acquiring its colour, smell, and disagreeable astrin- 

 gent taste. 



Animals cannot breathe it without suffocation — and, when unmixed 

 with air, it speedily kills all living vegetables. The solution of chlorine 

 in water was found by Davy to promote the germination of seeds. 



It does not exist, and is rarely evolved, [see Lecture V., p. 94,] in 

 nature in a free or uncombined slate, and therefore is not known to ex- 

 ercise any direct action upon the' general vegetation of the globe. It 

 exists largely, however, in common salt (chloride of sodium), every 100 

 lbs. of this substance containing upwards of 60 lbs. of chlorine. Indi- 

 rectly, therefore, it may be supposed to influence, in some degree, the 

 grovvth of plants, where common salt exists naturally in the soil, or is 

 artificially applied in any form to the land. 



Muriatic acid, the spirit of salt of the shops, consists of chlorine in 

 combination with hydrogen. It is a gas at the ordinary temperature of 

 the atmosphere, but water absorbs between 400 and 500 times its bulk 

 of it, and the acid of the shops is such a solution in water, of greater or 

 less strength. 



Muriatic acid has an exceedingly sour taste, corrodes the skin, and in 

 its undiluted state is poisonous both to animals and plants. It dissolves 

 common pearl ash, soda, magnesia, and limestone, with effervescence ; 

 and readily dissolves also, and combines with, many earthy substances 

 which are contained in the soil. 



