282 VINEGAR, CIDER, AND FRUIT-WINES. 



Crystallization is generally effected in stone-ware pots into 

 which dip a number of slender wooden rods. The pots are 

 placed in a warm room. Crystallization is finished in about 14 

 days. The crystals turn out especially beautiful when the acid 

 somewhat preponderates and the cooling of the solution is effected 

 very slowly. 



The salt forms dark green* rhombic prisms of a nauseous 

 metallic taste, which dissolve in 14 parts of cold and 5 parts of 

 boiling water, and are also soluble in alcohol. Heated in the 

 air the crystals burn with a green flame. 



Neutral cupric acetate contains in 100 parts, cupric oxide 

 39.8, anhydrous acetic acid 51.1, water 9. 



On heating, the dilute solution of the neutral salt yields acetic 



O/ 



acid and deposits a basic salt ; hence the use of strongly diluted 

 acetic acid or even distilled vinegar is not suitable for the prepa- 

 ration of crystallized verdigris. By long-continued digestion with 

 freshly glowed charcoal the dilute solution yields its entire con- 

 tent of copper to the latter ; hence vinegar containing copper can 

 be purified in this manner (2 or 3 per cent, of charcoal being suffi- 

 cient). The crystals of normal cupric acetate, after drying in 

 vacuo, lose no more water at 212 F., but give off 9 per cent, of 

 their water between 230 and 284 F. By destructive distilla- 

 tion cupric acetate yields strong acetic acid which contains acetone 

 and is contaminated with copper. Cuprous oxide (Cu 2 O) is obtained 

 111 red octahedral crystals when the neutral salt is heated with or- 

 ganic substances, such as sugar, honey, starch, etc. With the 

 acetates of potassium, sodium, and calcium, normal cupric acetate 

 gives double salts of a vivid blue color, which form fine crystals. 

 The chief use of normal cupric acetate in the arts is in making 

 pigments and for resisting the blue color which the indigo would 

 communicate in the indigo bath of the calico printer. In the 

 latter case its mode of action depends on the readiness with which 

 it parts with oxygen, whereby the indigo is oxidized before it 

 can exert any action on the cloth, being itself reduced to the 



* There is also another salt of a beautiful blue color, which contains, how- 

 ever, 5 equivalents of water (Wohler). It is prepared by exposing a solu- 

 tion of the salt mixed with free acetic acid to a low temperature. At 95O F. 

 it passes into the ordinary green salt. 



