286 VINEGAR, CIDER, AND FRUIT-WINES. 



wine until a sample of the filtrate is no longer colored blue by 

 ammonia, and then treating with distilled water, yields a fluid 

 which produces precipitates with barium chloride as well as with 

 ammonium oxalate, it consists of or contains gypsum; in the 

 other case heavy spar is present. 



Considerable quantities of the neutral as well as of the basic 

 cupric acetate arc used in calico printing, for painting in oil, and 

 for the manufacture of paints, especially of the so-called Schwein- 

 furth green, which is a crystalline combination of copper acetate 

 and arsenite. 



By gradually adding through a fine brass sieve a thin paste of 

 5 parts of verdigris rubbed up in 5 parts of lukewarm water 

 to a boiling solution of 4 parts of arsenious acid in 50 parts of 

 water, an amorphous yellowish-green precipitate is formed which 

 consists of copper arsenite and is called Scheele's green. By con- 

 tinuing the heating and adding acetic acid to the boiling mixture 

 it gradually becomes crystalline and acquires a very beautiful 

 green color; it is then known as Schweinfurth green, and only 

 requires washing with a little water and drying. The same com- 

 bination can also be obtained from cupric sulphate and sodium 

 arsenate and acetate. 



Schweinfurth green as found in commerce is a fine crystalline 

 powder of a lustrous green color, which, however, becomes paler 

 and loses some of its beauty by rubbing. It is insoluble in 

 water, but is decomposed by long-continued boiling in water and 

 then becomes brown. Like all copper salts it dissolves with a 

 blue color in ammonia and is decomposed by alkalies and alka- 

 line earths, pale-blue cupric hydrate being separated. By boiling 

 the mixture the cupric hydrate is first converted into black oxide 

 and then reduced by the arsenious acid to red oxide, the solution 

 now containing alkaline arsenate. Mineral acids and even glacial 

 acetic acid decompose the pigment by taking away the cupric 

 oxide and liberating the arsenious acid. 



Schweinfurth green is much used, especially in the manufacture 

 of colored .paper, wall-paper, artificial flowers, and light fabrics. 

 It is, however, very poisonous, and the use of articles dyed with 

 it has frequently caused sickness and even death by the dust 

 reaching the respiratory organs. 



