BULLETIN No. 77b. 
7 
when lime was not added; and in like manner shows the absence 
of such compounds when lime was present. White arsenic, it will 
be seen, dissolves very slowly, requiring more than ten days for 
complete solution, even in such a large volume of water, and at 
summer temperature. While the soluble portion of London purple 
goes in f o solution practically at once, and the same is approximately 
true of Paris green. 
London purple is, in the main, a mixture of arsenite of lime and 
arsenite of rosaniline. The latter is very soluble in water, to which 
it gives the red color so characteristic of London purple mixtures. 
It is from this rosaniline arsenite that the soluble arsenic is derived, 
and to which the ‘‘burning” of the foliage is, no doubt, due. The 
ready solubility of this compound also makes clear the reason that 
the injury to foliage from London purple mixtures is as great when 
freshly mixed as after having stood for days. The beneficial effect 
of lime in the London purple mixture is due to its decomposing 
action upon the rosaniline arsenite by which insoluble arsenite of 
lime is formed. This change takes place in a short time, as will be 
seen from the loss of color of the mixture. Double and triple 
weights of lime to London purple were experimented with, think¬ 
ing it might require these amounts to effect the decomposition, but 
an equal weight was found to be ample. 
The beneficial effect of lime in Paris green and White arsenic 
mixtures is also due to the formation of the insoluble arsenite of 
lime. Equal weight of lime to Paris green and White arsenic each 
was found sufficient in all cases, and no more than this, even of the 
commercial article, need be added to Paris green. But to be on the 
safe side, I think it best to add 2 pounds commercial lime (CaO) to 
1 pound white arsenic. One pound white arsenic (As 3 0 3 ) requires 
approximately 0.85 pounds of lime (CaO) to satisfy the reaction in 
the production of the insoluble arsenite, but slight excess of lime 
does not seem to do any harm—certainly far less than an excess of 
arsenic. 
II.— A Cheap Arsenite. 
A very cheap insecticide, having the same insecticidal properties 
as London purple, can be easily made by boiling together for one- 
half hour in 2 to 5 gallons of water— 
1 Pound Commercial White Arsenic, 
2 “ “ Lime, 
and dilute to required volume, say 100 gallons. The White arsenic 
can be obtained in quantities of 10 pounds for 8 to 12 cents per 
pound. Cost of lime will add very little to this. It is desirable 
