360 VEGETABLE SUBSTANCES. 



with a mordant of alum and tartar, but with different 

 mordants it may be made to assume all the shades 

 allied to red. The most permanent colours produced 

 from this dye are those in which the natural purple 

 red is changed by acids to an orange or yellow 

 colour. Brazil-wood is often used in dyeing silk of a 

 crimson hue, but it cannot be made so durable as the 

 cochineal crimson. 



Red ink is made of a decoction of this wood in 

 beer, wine, or vinegar, to which a portion of alum is 

 added, to render its colour less fugitive. 



Brazil-wood boiled in water communicates to it a 

 fine red colour, while the wood itself becomes of a 

 darker colour, and if the ebullition be continued long 

 enough the residuum will be black. Paper tinged 

 red with this decoction is altered to a violet colour 

 by the action of the alkalis, and to a yellow by most 

 of the acids. The action of sulphuric acid gas 

 renders it quite white. M. De Bonsdorff, in the 

 ' Annales de Chimie et de Physique,' details many 

 phenomena of the effects which this colouring matter 

 has on different acids. It is an excellent test to 

 detect the presence of sulphuric acid in vinegar. In 

 pure acetic acid it receives only a violet tinge, but 

 the admixture of only one two-hundredth part of sul- 

 phuric acid will give the stained paper a yellowish 

 instead of a violet hue. 



In two decoctions made with equal weights of 

 madder and of Brazil-wood, only half the quantity of 

 chlorine gas, which will destroy the colour of the 

 madder, is required to produce a like effect on the 

 Brazil-wood. More colour is extracted from this 

 wood by alcohol than by water. Warm marble 

 stained by the spirituous tincture assumes a purplish 

 red colour, which, on the heat being increased, changes 

 to a violet hue. If the stained marble be covered 



