A very fine, light brown powder, madefrom the flower-heads of species of pyrethrum. It is scarcely injurious to man. Three brands are on the market:

Persian insect-powder, made from the heads of Pyrethrum roseum, a species also cultivated as an ornamental plant. The plant is native to the Caucasus region.

Dalmation insect-powder, made from Pyrethrum cinerariae-folium.

Buhach, made in California from cultivated plants of Pyrethrum cinerariae folium.

When fresh and pure, all these brands appear to be equally valuable, but the home-grown product is usually considered most reliable. Pyrethrum soon loses its value when exposed to the air. It is used in various ways:

(1) In solution in water, one ounce to three gallons. Should be mixed up twenty-four hours before using.

(2) Dry, without dilution. In this form it is excellent for thrips and lice on roses and other bushes. Apply when the bush is wet. Useful for aphis on house plants.

(3) Dry, diluted with flour or any light and fine powder. The poison may be used in the proportion of one part to from six to thirty of the dilutent.

(4) In fumigation. It may be scattered directly upon coals, or made into small balls by wetting and molding with the hands and then set upon coals. This is a desirable way of dealing with mos-quitos and flies.

(5) In alcohol, (a) Put a part of pyrethrum (buhach) and four parts alcohol, by weight, in any tight vessel. Shake occasionally, and after eight days filter. Apply with an atomizer. Excellent for greenhouse pests. For some plants it needs to be diluted a little. (b) Dissolve about four ounces of powder in one gill of alcohol, and add twelve gallons of water.

(6) Decoction. Whole flower-heads are treated to boiling water, and the liquid is covered to prevent evaporation. Boiling the liquid destroys its value.

Good insect-powder can be made from Pyrethrum roseum, and probably also from P. cinerariaefolium, grown in the home garden.

Device for discharging the cyanide into the acid.

Fig. 1323. Device for discharging the cyanide into the acid.