178 DYEING. 



Bleaching of printed papers without destroying 

 the texture of the leaves. Steep the leaves in a 

 caustic solution of soda, and afterwards in one of 

 soap. Arrange the sheets alternately between 

 cloths in the same manner as paper-makers dispose 

 their sheets of paper when delivered from the 

 form. Put the leaves in a press, and they will be- 

 come whiter, unless they were originally loaded 

 with printers* ink or size. If this should not com- 

 pletely effect the whitening of the leaves, repeat 

 the process a second, or even a third time. 



Bleaching coloured rags to make white paper. 

 Soak or macerate the rags sufficiently ; put them 

 into a solution of caustic alcali, and then into the 

 oxygenated muriatic acid ; and, lastly, steep them 

 into diluted sulphuric acid. 



DYEING. 



Dyeing is the art of extracting the colouring 

 principle from different substances, and transfer- 

 ring them to wool, silk, cotton, or linen. When 

 other matters are coloured, the process is called 

 staining. 



In dyeing, the colouring matter is not merely de- 

 posited on the stuff, but is firmly attached to it by 

 chemical combination depending on an affinity 

 subsisting between them. 



If the colouring matters were merely spread 

 over the surface of the fibres of the cloth, the co- 

 lours produced might be very bright, but they 

 would not be permanent, since they would be 

 rubbed off, and would disappear when the cloth was 

 washed, or even by exposure to the weather. Dye- 

 ing is, therefore, a chemical process, consisting in 

 combining a certain colouring matter with fibres of 



