SULPHUR. 161 



instance of chemical combination, in which as is often 

 the case the properties of the constituents entirely /dis- 

 appear. When sulphuric acid is afterward used, the co- 

 lor re-appears, because the stronger acid has expelled 

 the weaker, and has itself no inclination to form with 

 the coloring matter a similar combination. 



387. STRAW BLEACHING. The bleach- 

 proccL If ie m f straw goods is always effected by 

 straw bleach- su lphurous acid. They are first moistened, 



and then exposed to the fumes of burning 

 sulphur. An inverted barrel is often made to serve 

 the purpose of a bleaching chamber. Articles thus 

 bleached by sulphurous acid, after a time, regain their 

 color. This is not the case in chlorine bleaching, be- 

 cause the coloring matter is not merely changed, but 

 destroyed. The agent is not applicable to straw, on 

 account of a faint brown tinge which it imparts to the 

 material. 



388. COPYING MEDAL- 

 ? LIONS. Sulphur melts, 



medallions by readily, by application of 



sulphur? *\ , :*. 



heat. At a higher temper- 

 ature, it thickens again. Still further 

 heating, makes it again fluid. In 

 this second period of fluidity, it has the remarkable 

 property of assuming a waxy consistence, on being 

 poured into water. In this condition, it is used for 

 copying seals, coins, and medals. The copy acquires, 

 in a few hours, the original hardness of sulphur. The 

 plastic material may be obtained in the form of elastic 



