88 PROCEEDINGS OP THE AMERICAN ACADEMY 



" Sdiweinfurt green is a double salt of acetic 'acid, arsenious acid, 

 and oxide of copper : it is entirely insoluble in water. All mineral 

 acids, and even concentrated acetic acid, extract the oxide of copper 

 from it, leaving the white arsenious acid bthind. It is also decom- 

 posed by fixed alkalies, except that in this case oxide of copper 

 remains behind. If the alkaline liquid, which has dissolved the 

 arsenious acid, is boiled with the precipitated oxide of copper, this is 

 reduced to the suboxide by the arsenious acid : the oxide, which is at 

 first black, becomes orange-red by boiling. . . . Ammonia dissolves it 

 without decompo:*ition, with the well known blue color of copper." 



Some Schweiiifurt green was now prepared by the first of these 

 receipts. 



Experiment No. 1. 



Took 20 grams verdigris and made it into a thin paste with water, 

 rubbing it well in a mortar to break up any lumps and mix thor- 

 oughly. IG grams of arsenic trioxide were dissolved in water, to 

 which about 1 gram of potassium carbonate was added : then the emul- 

 sion of verdigris was added to the boiling solution of arsenic trioxide, 

 which was made acid with acetic acid. At first yellow-green copper 

 arsenite was precipitated : this, on boiling, very gradually changed to 

 the aceto-arsenite, at first crystallizing in a pellicle over the surface ; 

 finally, with the addition of a little acetic acid, the whole mass became 

 more dense and crystalline, leaving a blue solution, from which the 

 precipitate was separated by a filter. The precipitate was washed 

 with boiling water, till no arsenic was fo\ind in the filtrate on testing 

 the acidulated liquid with sulphuretted hydrogen. The filtrate con- 

 tained copper, arsenic trioxide, and potassium acetate. 



The precipitate was dried at 100° C. for twenty -four hours, and then 

 analyzed. 



Analysis No. III. 



99.94 



The precipitate was of a pale green color, inferior to the samples 

 previously examined, and its specific gravity was much lower. 



The above receipt was now varied by substituting the neutral copper 

 acetate for verdigris : the manipulation is much easier than with the 

 basic acetate. 



