1 75 Method of manufaSlur'ing 



Each clufter weighs from five to fix pounds, Thcfe crj'flal?, 

 when broken, exhibit on their fra&ure a brilUant agreeable 

 green, inclining a Uttle to blue. 



Three pound.* of moift verdigrife are neceflary to make a 

 pound of cryftals. The indiflblved refiduum is rejefted as 

 ufelefs. Analyfis, however, having proved to me that a 

 great deal of copper in a metallic ftate, or weakly oxydated, 

 ftill exifts in it, I difpofed boards in the form of a ftagc 

 around uic manufaftor)' of C. Durand, and, forming ftrata 

 of about two inches in thicknefs with thefe remains, I foon 

 faw them covered with an efflorefcence of verdigrife. I took 

 care to moiilen them from time to time with vinegar, to dif- 

 folve the verdigrife as foon as a fufficicntly fi.rong efflo- 

 refcence was formed, and they were again difpofed in ftrata 

 to proceed as before, in order that T might derive as much 

 advantage from the reliduum as I fliould find convenient. 



There are fome manufaftories of the crj^ftals of Venus 

 where the verdigrife is prepared by means of vinegar diftilled 

 according to the method followed at Grenoble, which is 

 well underftood. All the operations tend to the fame end, 

 which is the folution of the copper in the acetous acid ; and 

 the purity of the materials renders it certain that there will 

 be no refiduum or lofs. But however fimple may be the 

 procefs for manufa6luring cryftallifed verdigrife, the high 

 price at which it is fold makes it to be much wi(hed that it 

 could be ftill rendered more fo. I made fome experiments for 

 thatpurpofe; but at prefent I ftiall confine myfelf to a fliort 

 view of my refults. We muft fet out from the principle, that 

 the acetous acid docs not attack copper in the ftate of a me- 

 tal, and that it cannot efiecl a folution of it but vi'hen re- 

 duced to an oxyd. The queftion then will be to difcover the 

 means of oxydating it in an economical manner. 



I ft, I expofed the plates of copper to the gazeous emana- 

 tions of the oxygenated muriatic acid in large glafs receivers, 

 connc6led together in the manner of adoptors, to which I 

 fitted a retort from which the acid was difengaged. 



2d, I took 



