294 CTHYMISTRY APPLIED TO AGRICULTURE. 



perfume to clothing. The vestimental essences are composed 

 of these. 



Spots occasioned by the juice of fruit may, when recent^ 

 be effaced by washing in water ; but, when of long standing, 

 this is insufficient, and sulphuric acid or chlorine (oxygenat- 

 ed muriatic acid) is employed. The last of these acids de- 

 stroys colors, and should therefore be applied only to white 

 fabrics : it is sometimes combined with an alkali, that it may 

 preserve its properties longer : in this state it is known by 

 the name of Javelte water. Sulphuric acid acts much less 

 upon colors, and is therefore preferred for such articles as 

 are dyed or printed. 



The spots produced by the oxide of iron are more lasting 

 than those occasioned by the oxide of any other metal. The 

 rust of iron, and some of the combinations of this metal, as 

 that which exists in writing-ink, when deposited upon cloth, 

 become fixed, and form a fast color. 



A faint spot of iron rust may be taken out by the applica- 

 tion of a weak acid ; spots of ink by sulphuric or muriatic 

 acid much diluted ; but the best method is that of covering 

 the spot with cream of tartar reduced to a fine powder and 

 then moistening it with water: after having allowed the 

 cream of tartar to remain some time, rub the cloth carefully 

 and rinse it. When an iron-rust spot is of a deep reddish 

 yellow color, these acids are not sufficiently strong, and re- 

 course must be had to oxalic, which may be used in the 

 same manner as the cream of tartar. The place of oxalic 

 acid may be supplied by the salts of sorrel of commerce ; 

 but the action of the latter is less perfect. 



CHAPTER XX, 



ON THE CULTIVATION OF WO AD, AND THE EXTRACTION OF 

 INDIGO FROM IT, 



For two centuries Woad (Isatis tincfaria) has been culti- 

 vated in Europe. This plant is biennial, and its hairy and 

 branching stalk rises to the height of three feet. As it is 

 not killed by frost, it affords excellent food for cattle during 

 the winter. It has however been less cultivated for fodder 

 than for yielding the only permanent blue color which was 

 known before the seventeenth century. 



