ACETATES AND THEIK MANUFACTURE. 285 



scraped off is made into a consistent paste by kneading with a 

 little water, and in this state is packed into leathern bags which 

 are placed in the sun to dry until the mass hardens and forms 

 the tough substance which constitutes the commercial article. 



In England, Germany, and Sweden copper sheets are moistened 

 with a solution of verdigris in vinegar and placed in a warm 

 room, or woollen cloths moistened with the above solution are 

 used, which are placed alternately with the copper sheets in a 

 square wooden box. 1 The woollen cloths are moistened with the 

 solution every three days for 12 or 15 days when small crystals 

 commence to form on the sheets. The sheets are then drawn 

 every six days through water and replaced in the box, but not in 

 direct contact with the woollen cloths, small disks of copper or 

 small pieces of wood being placed between each cloth and sheet. 

 The woollen cloths are now more thoroughly saturated than 

 before, but with a weaker solution. With a temperature of from 

 54 to 59 F., 6 to 8 weeks are required before the verdigris can 

 be scraped off. The product is not identical with that obtained 

 by the French method, it being somewhat poorer in acetic acid, 

 and hence its color is not bluish-green but almost pure green. 



According to Philipps the composition of the two varieties of 

 verdigris is as follows : 



English 



French crystallized 



verdigris. verdigris. 



Cupric oxide 43.5 43.25 



Anhydrous acetic acid .... 29.3 28.3 



Water . .' 25.2 28.45 



Impurities ....... 2. 



On account of having more body the globular verdigris is pre- 

 ferred by painters, notwithstanding its being more expensive and 

 less pure than the green article. It is frequently adulterated 

 with gypsum or chalk and also with heavy spar. If efferves- 

 cence is produced by pouring pure hydrochloric or nitric acid 

 over the verdigris and the filtrate precipitated by sulphuric acid, 

 chalk is present. If a white residue remains on digesting the 

 verdigris with an equal weight of acetic acid of 1.045 specific 

 gravity, gypsum or heavy spar has been added. In case this 

 residue, after washing with a mixture of acetic acid and spirits of 



