532 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



surface at first will appear dead, but will soon resemble the 

 finest gilding. The varnish should be kept in well -closed 

 vessels. 5 C\ XIIL, 1875, 104. 



GOLDEN VARNISH FOE LEATHER. 



This varnish, employed in imparting to leather a lustre 

 resembling that of the golden beetle, by simply brushing it 

 on with a broad brush, according to investigations of Bott- 

 ger, consists of a somewhat concentrated solution of fuchsin 

 in an alcoholic solution of shellac. 14 (7, CCXIIL, 1874, 531. 



PREVENTION OF YELLOWING OF WHITE PAINT. 



Dr. Ludersdorff, of Berlin, regarded the oil employed as 

 the sole cause of the yellowing of white paint, when light 

 and air are excluded ; and since the oil acts simply by reason 

 of its conversion, by oxidation, in drying, into a peculiar 

 resin, which forms the sole binding material of the pigment, 

 and renders the paint durable, he suggested a solution of 

 some colorless resin as a substitute for oil in the prepara- 

 tion of white paint ; and it was found, on trial, that a coating 

 of white paint prepared on this plan remained unchanged in 

 color after two years and a half. The number of resins 

 adapted to this purpose is not as great, however, as might 

 at first be supposed, since they must be colorless, especially 

 for white paint, and hard enough to form a durable paint, 

 and at the same time cheap enough, and should not require 

 too expensive a solvent. Shellac, one of the very best in 

 these respects, however, has the peculiarity of acquiring a 

 reddish tint with carbonate of lead, unless it is bleached, in 

 which form it is too expensive. Gum copal is not only ex- 

 pensive, but requires an expensive solvent. Rosin is too 

 brittle, except perhaps in cases where a great degree of 

 hardness may not be required. Sandarac, one of the hard- 

 est and least colored resins, and dammar were however 

 found to answer. Among the solvents, alcohol and oil of 

 turpentine alone were found of practical value, though not 

 capable of substitution for each other ; thus copal, shellac, 

 and sandarac require alcohol, and dammar turpentine, and 

 while rosin is soluble in ether, it will only dry rapidly enough 

 when used with alcohol. For sandarac solution, 7 ounces of 

 the gum, carefully freed from pieces of bark, etc., and 2 ounces 



