148 SHEET FABRICS. [V. 



same as the Indian hair-dye, and acts by forming sulphuret 

 of lead with the sulphur of horn, producing dark spots, that 

 contrast with the lighter color of the horn. 



Ivory hardened. — It is said that ivory which has become 

 friable by age, will recover its original hardness by being 

 boiled, for some time, in a solution of gelatin. 



Ivory rendered Soft and Translucent. — This process of 

 Geisler, communicated by Dr. Eisner, is as follows. Small 

 pieces of ivory are laid in strong phosphoric acid (spec. grav. 

 1.13) until they become transparent, then rinsed in water and 

 dried in pure linen. When dry, it is translucent, and hard, 

 but softens as often as it is dipped in warm water or milk. 

 The time of immersion in the acid dijQfers with different pieces 

 of ivory. If certain parts are to retain their original charac- 

 ter, they are covered with a varnish before immersion. The 

 acid probably acts by forming an acid phosphate of lime out 

 of the basic phosphate which constitutes f of ivory. 



Etching on Ivory. — The ivory is to be covered with wax 

 and the designs traced with a style, and then eaten in by a 

 strong solution of nitrate of silver made by dissolving 6 grm. 

 silver in 30 grm. nitric acid and 150 grm. water. Exposure to 

 light, after the removal of the wax by hot distilled water, 

 will blacken the color of the traces. By substituting gold, 

 platinum, or copper nitrates, other colors may be obtained. 



Ivory Etched in Colors. — The ivory is coated like a copper 

 plate, with an etching ground, a design graved through the 

 ground, and then etched by a solution of 120 gr. pure silver 

 dissolved in a fl. oz. nitric acid and diluted with 1 qt. water. 

 In the course of | to 1 hour, according to the depth of shade 

 required, the liquid is poured off, the ivory washed, and dried 

 by paper, then exposed for an hour to sunlight, and the ground 

 removed by terpentine. The color is brown or black. Other 

 colors are obtained by nitrate of copper, chloride of gold, or 

 of platinum. 



Caoutchouc. — The great expansion which the application 

 of caoutchouc to various fabrics has received within a few 

 years past, is largely, if not mainly, due to the persevering 



