409 
using' Paris green is the readiness with which it settles to the bottom 
of the tank or reservoir of the spraying apparatus. This is because 
it is a rather coarse powder, very much Jess finely divided than Lon- 
dou purple, which latter fact gives the purple a certain advantage. 
A recent conversation with one of the leading manufacturers of Paris 
green has brought out the fact that this coarseness of grain and the 
acconrpanying difficulty in using Paris green in water suspension are 
quite unnecessary. It seems that the market has hitherto demanded 
a very dark-colored article, the lighter color having been deemed to 
indicate adulteration. It seems, however, that the darker color is 
simply due to the larger size of the crystals, the darkest green having 
the largest crystals. If the green were reduced to an impalpable powder, 
which would make it much more satisfactory as an insecticide, it would 
lose the intensity of its color and become whitish. This manufacturer 
tells me that for a number of years he was able practically to control 
the market, because he had discovered a means of crystallizing the 
green in unusually large particles, securing a a t cry dark-colored product, 
although he was aware that for the use intended the product so obtained 
was much less valuable. Yet the darker green, with its accompanying 
larger-sized crystals, is more difficult to manufacture, and hence more 
expensive. 
It seems, therefore, that all these years we have been using a poison 
which could have been had at less expense and in a much more satis- 
factory form. 
Steps were therefore taken to secure a quantity of pulverized Paris 
green which was made in the ordinary way, except that it was reduced 
by the manufacturer to a nearly impalpable powder. The results were 
eminently satisfactory, and would have been more so if the pulveriza- 
tion had been carried to the fullest degree. This product remained in 
suspension three times as long as the ordinary Paris green, and the 
advantage of the fineness in division will undoubtedly be apparent in 
its use against insects. 
It may be interesting to know the process of manufacture of this 
arsenical. Powdered white arsenic (arsenious oxide) is combined with 
sodium carbonate in a large vat of boiling water. A chemical change 
results, in which the sodium unites with the arsenic, forming sodium 
arsenite, and carbonic acid gas is given off. Sulphate of copper or 
blue vitriol is dissolved in another large vat, and is then combined in a 
still larger vat with the sodium arsenite already obtained. A precipi- 
tate of arsenite of copper forms on the commingling of the two liquids 
and sodium sulphate which remains in solution. Acetic acid is added 
to the mixture thus obtained and unites witli the precipitate of arsen- 
ite of copper, forming an aceto-arsenite of copper, or more properly, a 
double salt of copper with arsenious acid and acetic acid. This is 
insoluble in water, and appears as a line, green, crystalline product, 
which, when properly dried, is ready for the market. 
