168 CHYMISTRY APPLIED TO AGRICULTURE. 



M. Gay-Lussac, who has made a series of experiments 

 upon prussic acid, found it to consist of carbon, azote, 

 and hydrogen, combined in the following proportions ; 



Carbon 44.39 



Azote 51.71 



Hydrogen 3.90 



The two first elements of this composition form a radi- 

 cal, which our distinguished author calls cyanogen : the 

 combination of this with hydrogen constitutes the prussic 

 or hydrocyanic acid. There exists in this acid no trace 

 of oxygen, nor is it the only instance of the kind, which 

 modern chymistry affords us. 



Combined with iron, prussic acid forms the valuable 

 substance known by the name of Prussian blue, the use 

 of which is so important in coloring and painting, M. Ray- 

 mond has discovered a method of fixing this color so 

 successfully upon silk, that indigo has almost disappeared 

 from the coloring establishments of Lyons : a son of 

 M. Raymond has been equally successful in his use of it 

 for woollen manufactures. 



The vegetable kingdom furnishes many other acids, as 

 the benzoic, gallic, mucic, . kinic, &lc. ; but as they are 

 less abundant, and their uses very limited, I do not think 

 it necessary to give here any account of them. 



ARTICLE XL 



The Fixed Alkalies. 



Potash is found, in greater or less quantities, in all 

 vegetables ; soda generally in plants growing near the 

 sea, or in soils impregnated with marine salt. 



The most convenient mode of obtaining potash is by 

 burning vegetable substances, leaching the ashes, and 

 evaporating a solution of them to dryness : this first prod- 

 uct is known under the name of salts, and is employed in 

 the arts; it is colored, but becomes white by being cal- 

 cined in a reverberating furnace ; it is then known by the 

 name of pearlash. 



As the use of the salts and of pearlash in the arts is very 

 extensive, and as there are few localities where they may 



