RESINS. 213 



solution, it readily combines with the base, and forms 

 a soluble salt — a compound of the acids of the 

 resin with the alkali. 



639. This property of resins of -dissolving in alka- 

 lies is practically employed by the paper-makers, 

 who prep are a size for the commoner sorts of paper 

 by dissolving resin in a solution of carbonate of 

 soda. Such a solution is immediately decomposed by 

 any of the strong acids, which combine with the 

 soda, and separate the resinous acid in an insoluble 

 state. For the same reason, too, resin is used as a 

 constituent of common yellow soap. . 



540. There are likewise found a number of gum- 

 resins, as they are called, which have some of the 

 properties of gum, and yet resembles resins ; these 

 are mixtures of gum and resin. They dissolve, though 

 but imperfectly, in both water and spirit of wine. 



541. Plants contain an immense variety of dif- 

 ferent coloring matters, all of which, however, when 

 analyzed, are found to consist of nothing but oxygen, 

 hydrogen, and carbon, or these three with the addi- 

 tion of nitrogen. The nature and properties of these 

 substances are as various as their colors. They are 

 all destroyed by heat, which burns them, like all the 

 other varieties of organic matter. When burnt, the 

 results are water, carbonic acid, and frequently am- 

 monia. 



542. Some vegetable colors are tolerably perma- 

 nent, whilst others are very fugitive, fading in a short 

 time when exposed to air and light, &c. Most vege- 



