RESINS. 385 



which is afterward polished with rotten stone. Copal 

 varnish is also similarly used. Shellac, dissolved in 

 soda or potash, is sometimes used to give body to 

 paints, as a substitute for part of the more expensive 

 material. 



What i rosin 964. ROSIN SOAP. The resins possess 

 soap? an ac id character, and like fats, form soap 



with the alkalies. Common rosin is largely consumed, 

 with fat and potash, in the manufacture of common 

 brown soap. The greater hardness which it imparts 

 depends on the formation of a certain portion of rosin 

 soap, in the mixture. 



965. SIZING. The soap which is 



How is rosin 



used in sizing formed on boiling rosin with strong potash 

 paper? - g uge( j m s j zni g p a p er . Being mixed with 



the material from which paper is to be made, a solution 

 of alum is afterward added to the pulp, and a compound 

 of rosin and alumina thus produced in every portion of 

 the mass. The pores of paper made from this mate- 

 rial are thus completely filled, and the spreading of 

 the ink prevented. A surface sizing which is less ef- 

 fectual, is also given to paper by a solution of glue, 

 applied after the paper is formed. When this is de- 

 stroyed by erasure, its place may be supplied, and the 

 spreading of ink prevented, by rubbing powdered rosin 

 upon the spot from which the sizing has been removed. 

 966. SEALING-WAX. Sealing-wax con- 



What is the 



tionof sists, principally, of shellac. Venice tur- 

 pentine is added to make it more inflam- 

 mable and fusible, and vermilion or lamp-black to color 



it. Ship pitch is resin changed and partially decom- 



17 



cotnposi 

 sealing-icax ? 



