PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 407 



BLEACHING. 



The oldest modc*of bleaching, ■V7hich is technically termed croflwg, con- 

 sists in exposing- the straw to the action of dew and light by spreading it 

 out in meadows and frequently turning it while the process is going on. 



It is next gathered, assorted and submitted to. the action of steam for 

 the purpose of extracting its color, and then a fumigation of sulphur to 

 complete the bleaching. The straws arc then in a condition to be plaited 

 or woven. 



Where and when the practice of bleaching first began, we have no ac- 

 count. But we know that it is of very ancient origin, mention being made 

 of it in the oldest books extant. 



And from the earliest description to the close of the last century it is 

 quite clear that no other process was known, than what has already been 

 alluded to ; and in case of cloth, alternate boiling and exposure to the 

 atmosphere — a process requiring many months to complete, but since the 

 application of chlorine to this purpose the process is completed in a few 

 days, and for most of dyeing operations in a few minutes. 



Professor Graham observes of the application of chlorine to this purpose 

 as one of the most valuable which chemistry has presented to the arts. 



Phlorine was discovered by Scheele, in 1114, and was called by him 

 dephlogisficated muriatic acid. 



About eleven years after this, Berthollet considered that he had found it 

 to be a compound of muriatic acid with oxygen, and hence called it oxyge- 

 nized muriatic acid. This was afterwards contracted into oxymuriatic acid. 



In 1811 Sir Humphrey Davy discovered it to be a simple or elemeiitary 

 substance, and gave it the name of chlorine, from the fact af its having a 

 greenish yellow color. 



Scheele described its peculiar property of destroying vegetable coloring 

 matters ; but Berthollet was the first to call the attention of the public to 

 its value as a bleaching agent in 1185. iVbout the time this chemist was 

 investigating the nature of this substance, he was visited by the celebrated 

 James Watt, to whom Berthollet related the results of his experiment upon 

 bleaching,* and from this circumstance the inventor of a steam engine 

 became also the introducer'of the new process of bleaching into Great 

 Britain. 



Some give this honor to Professor Copeland, of Aberdeen; but Professor 

 Napier gives it as his opinion, from the evidence he has seen, that it belongs 

 to Watt, although there was little difference of time. 



Tiie first method of using chlorin^ was by saturating cold water with the 

 gas, the water taking up about twice its volume of it. The goods were 

 put into this water, after which it was heated to drive off the chlorine or 

 set it free, that it might act upon the coloring matter. But the goods 

 were impaired by this process, and more diluted solutions were employed 

 and found to bleach equally well, ai\d the goods were preserved. 



But a defect of the goods becoming yellow after a few days, suggested 

 alternate boilyigs with alkaline lyes ; and the difficulty of the workmen, 

 being unable to endure the effects of the escaping gas, led to the discovery 

 that alkalies not only absorb a greater quantity of chlorine than water, 



