L. TECHNOLOGY. 459 



burnt in by means of a muffle in less than a minute. This 

 enamel, applied to a viscous glass, is recommended for plant- 

 labels, guide-boards, numbers of houses, etc., and it can be 

 employed in the preparation of photographs without the use 

 of collodion. For this purpose a mixture often parts of gum, 

 one part of honey, and three parts of bichromate of potash, 

 properly filtered, is to be dried upon the enamel and then ex- 

 posed in the camera, after which the image is developed by 

 dusting over it a powder, consisting often parts, by weight, 

 of the oxide of cobalt, ninety parts of finely pulverized iron 

 scales, one hundred parts of red lead, and thirty parts of sand, 

 and the chromate is decomposed by immersion in a slightly 

 acidulated bath (one hundred j>arts of water and five of hy- 

 drochloric acid). After washing and drying, the enamel is to 

 be melted by placing it upon a piece of sheet-iron carefully 

 cleansed, and coated with chalk, for which a minute will suf- 

 fice, and the photograph glazed upon the enamel is then 

 brought to view. 6 C, January 27, 38. 



WINDOW PUTTY. 



An excellent window or glass putty may be made by boil- 

 ing seven parts of linseed oil two or three hours with four 

 parts of ground umber, and mixing four parts of yellow wax 

 in the heated mass. The oil is then to be removed from the 

 fire, and, while still warm, is to be kneaded up with five and 

 a half parts of finely precipitated chalk and eleven parts of 

 ground white lead. 5 C, xl., 320. 



FASTENING RUBBER TO WOOD OR METAL. 



The adhesion of sheets or plates of India-rubber to wood 

 or metal can, it is said, be readily accomplished by the use of 

 an ammoniacal solution of shellac. To prepare this substance, 

 the bleached shellac is to be powdered and soaked in ten 

 times its weight of purified aqua ammonia, when it swells to 

 a slimy mass, and liquefies in the course of three or four 

 weeks. This substance, when applied to wood or to iron, 

 will, it is asserted, be found to answer the desired purpose. 

 The ammoniacal solution softens the rubber, and in drying 

 hardens with it, and on the surface of condensation forms a 

 coating impenetrable to gases or liquids. 13 (7, August 11, 

 1139. ' 



