For use on dormant trees, dilute with from 5 to 7 parts of water. For killing plant-lice on foliage dilute with from 10 to 15 parts of water. Crude oil emulsion is made in the same way by substituting crude oil in place of kerosene. The strength of oil emulsions is frequently indicated by the percentage of oil in the diluted liquid: — For a 10 per cent emulsion add 17 gallons of water to 3 gallons stock emulsion.

For a 15 per cent emulsion add 101/3 gallons of water to 3 gallons stock emulsion.

For a 20 per cent emulsion add 7 gallons of water to 3 gallons stock emulsion.

For a 25 per cent emulsion add 5 gallons of water to 3 gallons stock emulsion.

Lead, arsenate of. — See under Arsenicals, p. 291.

Lime-sulfur. - A compound of lime and sulfur makes both a good insecticide and a good fungicide (for an account from the fungicide point of view, see page 256). There are several forms of it, as (1) the ordinary dilute home-made ; (2) the concentrated home-made ; (3) the commercial concentrated brands ; (4) the so-called self-boiled preparation. The three first are solutions, and are modifications of one preparation ; the self-boiled is mostly a mechanical mixture of the lime and sulfur.

1.  Home-made dilute solution of lime-sulfur. - Quick lime, 20 pounds; sulfur (flour or flowers), 15 pounds; water, 50 gallons. The lime and sulfur must be thoroughly boiled. An iron kettle is often convenient for the work. Proceed as follows: Place the lime in the kettle. Add hot water gradually in sufficient quan-tity to produce the most rapid slaking of the lime. When the lime begins to slake, add the sulfur and stir together. If convenient, keep the mixture covered with burlap to save the heat. After slaking has ceased, add more water, and boil the mixture one hour. As the sulfur goes into solution, a rich orange-red or dark green color will appear. After boiling sufficiently, add water to the required amount and strain into the spray tank. The wash is most effective when applied warm, but may be applied cold. If one has access to a steam boiler, boiling with steam is more convenient and satisfactory. Barrels may be used for holding the mixture, and the steam applied by running a pipe or rubber hose into the mixture. Proceed in the same manner as for boiling in the kettle until the lime is slaked, when the steam may be turned on. Continue boiling for forty-five minutes to an hour, or more if necessary to get the sulfur well dissolved.

This mixture can be applied safely only when the trees are dormant, — late in the autumn after the leaves have fallen, or early in the spring before the buds swell. It is mainly an insecticide for San Jose scale, although it has considerable value as a fungicide for certain diseases, like the peach leaf-curl. As the San Jose scale is not killed unless the solution comes in contact with it, great care should be exercised to completely cover the branches.

2.  Home-made concentrated lime-sulfur wash.

For making the concentrated mixture, the steps are the same as in making the usual boiled wash, but the following formula should be used: —

Insecticidal Substances Part 3 120

Slake the lime, make a thin paste, and add the sulfur. Flowers of sulfur or light or heavy sulfur flour may be used. The lime should be fresh lump lime, free from dirt and grit, containing 90 per cent or more of calcium oxide and less than 5 per cent of magnesium oxide. Stir thoroughly during the hour of cooking, to break up the lumps of sulfur. Enough water should be added at the start so that the evaporation will not leave the quantity less than 50 gallons when the cooking is ended. If kettles are used, 10 to 15 gallons additional will be needed, while with steam none may be required. The kettles should be considerably larger than the amount of wash to be made, to prevent loss of material by boiling over. The clear liquid should be drawn off into tight containers if to be kept any considerable time ; and stored where there is no danger of temperatures much below freezing. For use, test the clear solution with the hydrometer, and dilute as indicated in the table: —