SILK. 



183 



a few decigrammes of magenta in 28 to 30 cubic centimetres of water, 

 and heated to boiling. During ebullition, caustic soda must be added to 

 it drop by drop, till a pale rose colour only remains in the liquid. The 

 liquid must be removed from the fire, and the sample immersed in it for 

 some minutes, after which it must be removed and dried. 



Silk and wool are dyed by this treatment, while the vegetable fibres 

 remain colourless. Wool may be detected in silk by the presence of 

 sulphur. If it is immersed for a time in a plumbate of soda prepared 

 by dissolving lead hydroxide in caustic soda, the silk will be colourless and 

 the wool black ; or a piece of the tissue 2 centimetres square may bo 



Fig. 117. Wood pulp silk. 



boiled in 10 to 12 cubic centimetres of Schweitzer's solution. In from five 

 to ten minutes the silk will be dissolved. If the silk is black, double 

 the volume of Schweitzer's solution should be added, and the mixture 

 soaked from ten to twelve minutes. The undissolved wool should be 

 then removed and the liquid quickly neutralised with nitric acid. Silk 

 will remain in solution, while cellulose will be precipitated. Hydro- 

 chloric acid is a solvent of silk, while it leaves wool and cotton unacted 

 upon for a lengthened period. 



Sea Silk. The marine products of the ocean have been investigated, 

 with some success, in order to obtain a silk, independent of the silkworm 

 culture, that may be used as a commercial article. This material has been 



