Arsenite of Lime Solutions. - John N. Dixon in 1877 and 1878 used a weak solution of white arsenic (155. Evolution of Spraying). With increased experience he wrote in 1881: "I consider the arsenic solution as complete a remedy for the codling-moth as for the canker-worm. When the apples are from the size of a bird-shot to that of a pea, if the orchard is carefully sprinkled with arsenic water at the rate of one pound of white arsenic to two hundred gallons of water it will not leave a canker-worm, codling-moth, tent-caterpillar, or buculatrix in the orchard. In view of this perfect and inexpensive remedy, we do not now consider these insects as any serious obstacle in the way of successful apple-growing, and we cannot see any reason why the remedy might not be successfully used on garden insects and on the grasshopper, cotton-worm, army-worm, Hessian-fly, and chinch-bug. One man with a driver and team can sprinkle twenty acres in a day for protection against any of these insects."*
But some entomologists yet prefer the Paris green, London purple, or other forms of the arsenites. The reasons given are that they are safer and less liable to burn the foliage than pure arsenic. But the writer can see little force in this argument, as John N. Dixon and others have found that one pound of white arsenic to four hundred gallons of water will do the work with the canker-worm, codling-moth, strawberry-worm, and tent-caterpillar, and this will not harm the tenderest foliage.
Until recently entomologists have not favored the use of pure arsenic, but the Paris green and London purple are so variable in quality as sold by druggists, and white arsenic is relatively so pure, that definite proportions can easily be secured. So a change in opinion is now evident in several States. At this time the spraying calendars give such statements as that of Professor Summers, who says: "As white arsenic, as found in the market, is little liable to adulteration, this insecticide is less liable to vary in strength than Paris green. The cost of materials is also somewhat less, and when an arsenite is to be used in such large amounts that the trouble of preparing is not an important item we strongly recommend the use of this compound." But lime or sal soda is now used in solution with the arsenic. This changes the color of the stock mixture, making it safer to store for further use, and it is claimed that it is less liable to burn the foliage. The approved formula now used is to boil in the open air one pound of white arsenic and four pounds of sal soda with one gallon of water until dissolved. This kept in a jug labelled "Poison" constitutes the "stock mixture." When wanted for use add the milk of three pounds of fresh lime, strained to remove sediment, to forty gallons of water. Into the lime solution pour one pint of the stock mixture and mix thoroughly by stirring. This is the formula used in spraying for codling-moth, canker-worm, and all insects that eat foliage or fruits.
* Premium essay by Hon. J. N. Dixon, published in Iowa Horti-cultural Report, 1882.
In spraying with Paris green the formula used is one pound of Paris green and one pound of fresh lime in two hundred gallons of water.
Even where the slaked lime water is strained this mixture is apt to clog the sprayer and its strength is not as uniform as in the use of the arsenic and soda, and the same is true at this time of London purple.