ALKALIES. 241 



from the air, as speedily to change the color of any of the alkaline 

 test papers upon which it is laid. Turmeric paper shews it well. 

 Crystallized hydrate of potassa, produces cold during its solution in 

 water, while the solid alkali evolves heat. 



5. COMPOSITION. See potassium. 



6. POLARITY. Electro positive ; it is attracted to the negative 

 pole in the galvanic circuit. 



7. ORIGIN. 



From vegetables that have no connexion with salt water. Plants 

 yield more than trees ; the branches more than the trunk ; the small 

 branches more than the large, and the leaves most of all. Her- 

 baceous plants yield more ashes and more alkali than wood. Fumi- 

 tory* is said to yield more salt than any other plant, and wormwood 

 more alkali than any other vegetable. 



One thousand pounds of the following vegetables yielded saline 

 matter in the following proportions. 



Wormwood, 748 Fumitory, 360 



Stalks of sunflower, 349 Beech, - 219 



Stalks of Turkey Wheat, or Elm, 166 



Maize, - 198 Fir, - - 132 



Vine branches, - 162 6 Oak, - 111 



Fern, cut in Aug. ^ - 116 Heath, - - 115 



Sallow, - . - 102 Aspen, - 61 



Box, - 78 Kirwan. 



Fern leaves are used in Yorkshire, in England, in cleaning cloth 

 for fulling, and appear to afford alkali already developed. 



In the Highlands of Scotland, soap is made from the alkali ob- 

 tained from the ashes of peat. 



The resinous and odorous woods afford little alkali ; hence the 

 ashes of pine wood are regarded in families, as worthless for soap- 

 making. 



Potatoe tops yield a great deal of alkali. 



The alkali of ashes arises principally from salts existing in the veg- 

 etable juices, and modified by the fire.f 



8. HISTORY. 



In an impure state, it was known to the ancients ; Pliny states that 

 the Gauls and Germans formed soap of ashes and tallow ; and Dr. 

 Thomson thinks that their ashes were the same with our potash. 



* In Mr. Kirwan's table, quoted in the text, Fumitory is stated to yield but about 

 half as much saline matter as wormwood. 



t As the alkali of vegetables is not an essential constituent, and is derived from the 

 soil, the quantity which any plant will afford, will depend on the qualities of the 

 earth, in which it is raised. Hence we can account for the discrepancies of different 

 experimenters respecting the relative quantities of alkali afforded by different plants. 

 J. T. 



31 



