238 



BLEACHING 



put out to sun for a week; that is, the unbleached fabrics 

 were spread on the grass and exposed to the bleaching action 

 of sun and dew. 



218. An Artificial Bleaching Agent. While the sun's rays 

 are effective as a bleaching agent, the process is slow; more- 

 over, it would be impossible to expose to the sun's rays the 

 vast quantity of fabrics used in the civilized world of to-day, 

 and the huge and numerous bolts of material which daily 

 come from our looms and factories must therefore be whitened 

 by artificial means. The substance almost universally used as a 

 rapid artificial bleaching agent is chlorine, best known to us as a 

 constituent of common salt. Chlorine is never free in nature, 



but is found in com- 

 bination with other 

 substances, as, for 

 example, in combina- 

 tion with sodium in 

 salt, or with hydrogen 

 in hydrochloric acid. 



The best laboratory 

 method of securing 

 free chlorine is to 

 heat in a water bath a 

 mixture of hydrochlo- 

 ric acid and manganese 

 dioxide, a compound 

 containing one part of 

 manganese and two 

 parts of oxygen. The 

 heat causes the man- 

 ganese dioxide to give 



FIG. 158. Preparing chlorine from hydrochloric 

 and manganese dioxide. 



up its oxygen, which immediately combines with the hydro- 

 gen of the hydrochloric acid and forms water. The man- 



