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XXXIX. Observations on the Plant called Si. John's 

 IForL By C. B.\ u x ac h * . 



&T. John's wort is a vcrv common plnnt, which grows 

 in great abundance in the fields, in the woods, and in uncul- 

 tivated places. Botanists have described its distinguishing 

 characters under the name of hypericum perforatum : it is 

 employed in medicine as an excellent vulnerary and balsamic 

 remedy ; but unfortunately its juice is of little utility, since 

 it is unknown to the greater part of dyers, in whose art, 

 however, it may be applied with success. St. John's wort 

 is a resinous plant, the flowers and summits of \\ hich, filled 

 with seeds, contain a juice soluble in water, in alcohol, and 

 vinegar : it diffuses throughout the first two liquids a red 

 colour like that of blood, and in the latter a most splendid 

 and beautiful crimson : when com!)incd with acids or me- 

 tallic solutions it presents a beautiful yellow colour ; which 

 proves that it coiittains two colouring matters, one more 

 soluble than the other, that is the red. 



To dye cloth, wool, silk, and cotton, yellow, it is suffi- 

 cient to immerse them in water properly impregnated with 

 the juice of this plant and a certain quantity of mordant. 

 The salt best for being used as a mordant with this colour 

 is sulphate of alumine, combined with a proper proportion 

 of potash (carbonate of potash), in which the stufi's are suf^ 

 fered to remain some time ; for it is on the length of the 

 time, the quantity of the mordant, ajid the heat employed, 

 that the fixity of the colour, and the shades resulting from it, 

 depend. When little mordant is used, the dye is of a yel- 

 low colour; by increasing the mordant it inehnes to green; 

 and by adding solution of tin in nitro-muriatic acid it as- 

 sumes rose, cherry, snd crimson shades, all very beautiful. 

 The alum, generally employed for all extractive dyes, does 

 not succeed well in the process here alluded to : the addition 

 of potash is essentially necessary, because it decomposes this 

 salt, precipitates its earth, dissolves a considerable portion 

 of it ; afid it is this alkaline salt with an earthy base which 

 in this operation becomes the true mordant, especially as 

 the colouring principle resides in a matter almost purely 

 resinous. 



The juice of St. .John's wort united to the mordant here 

 mentioned gives to paper a beautiful yellow colour; and as 

 it produces the same effect on skins, leather-dressers may 

 employ it with advantage for dyeing white sheep- and other 

 skins, 



* From the Annates de Cbi'ir.ic, No. 137. 



ThG 



