(93) 



of permanence and durability; also that they are very 

 hard, for which reason they take and retain a high polish. 

 Many resins of recent production and of less value, are 

 added to the cheaper varieties of varnish. Our collection 

 contains representatives of practically all varnish resins 

 that are in use. 



Miscellaneous Resins. Cases 43 and 44. — Resins are 

 waste substances produced by the life processes of the 

 plant. They are transported through the plant body in a 

 liquid state, being dissolved, mostly in volatile oils. When 

 the ducts or cavities containing them are broken or cut, 

 they exude upon the surface and may then harden by the 

 evaporation of the oil. They are collected for use by va- 

 rious methods, some of which are illustrated by the speci- 

 mens and pictures exhibited in the cases. 



Dye Stuffs. Case 45. — Many of the substances pro- 

 duced by the living plant and stored in its body possess 

 colors which can be imparted to fabrics or other articles 

 immersed in their solutions. There are others which, 

 although themselves not colored originally, yield useful 

 dyes when some chemical agent is added to them. All 

 such plant substances, as well as the vegetable tissues 

 containing them, are known as "dye stuffs." Good 

 illustrations are logwood, brazil-wood, madder, alkanet, 

 and indigo, besides which, many of less importance are 

 to be seen in our collection. 



Although the use of anilin or coal-tar colors has very 

 largely replaced that of vegetable dyes, there is still a vast 

 use of the latter. But for the introduction of the former, 

 it is difficult to see how the demand for colors could have 

 been supplied under modern conditions. 



Tanning Materials. Cases 46 and 47. — The tanning 

 materials are also very important from an economic stand- 

 point. They depend for their value chiefly upon the 

 tannic acid that they contain, but that other constituents 

 contribute is clear from the fact that a substance containing 

 less tannin may be more valuable than one containing a 



