M. TECHNOLOGY. 607 



artificially up to about 79. The article should acquire this 

 temperature by several hours' previous exposure to it in the 

 shop, and should then be smoothed, washed, and rubbed dry 

 with chamois leather or silk. All dust, dirt, and moisture 

 are to be removed by means of a brush of suitable size with 

 pure, soft, firm bristles, the use of any form of oil or grease 

 being avoided. The varnish must be laid on with exceeding; 

 care, dipping the brush lightly into it, and beginning a short 

 distance from the edge, and working by direct, long, rapid, 

 uniform sweeps of the brush, of even pressure, to the edges 

 and corners, at each side alternately, until the film has the 

 thickness of paper. The article should then be exposed to 

 the sun, or artificial heat, protected from draft and dust; 

 since cold or draft would darken the varnish. In this latter 

 case the brilliancy and clearness can only be restored by 

 thinly recoating the surface with the varnish and exposing it 

 directly to the fire, that the spoiled part may be redissolved, 

 taking care not to put it so near that it will scale off. 5 C, 

 1873,230. 



NEW METHOD OF SILVEKING GLASS. 



An improved method of silvering glass and other sub- 

 stances, devised by Mr. Siemens, consists in the use of alde- 

 hyde of ammonia, obtained by j^assing a current of dry am- 

 monia through aldehyde. He makes two solutions of four 

 grammes of nitrate of silver and two and a half grammes of 

 aldehyde of ammonia, and then mixes the solutions and filters 

 them. The object to be silvered is first washed with a solu- 

 tion of carbonate of potassa, then with alcohol, and finally 

 with water. It is then brouoht in contact with the silverinsf 

 solution, and subjected to the heat of a sand-bath. A deposit 

 of metallic silver immediately takes place, and the tempera- 

 ture is carried up to 130 or 140 Fahr. When the deposit 

 is sufticiently formed, the article is to be removed and rinsed 

 with distilled water. ^ B^Jime 26, 1873, 329. 



TIXXIXG LINEN AND COTTON EABRICS. 



The following process is given by R. Jacobsen for coating 

 linen and cotton fabrics w4th a heavy, flexible, brilliant film 

 of tin. A thin paste, formed by stirring commercial zinc 

 dust into a solution of egg-albumen, is laid on the fabric by 



