There has been for years a prejudice against the use of this gas, both from the danger to the plants and to the person using it. In the quantities we used it seven or eight years ago it was dangerous to both unless every precaution was taken. The necessity of opening the windows in half an hour after the mixing was most inconvenient and a nuisance.
After repeated experiments at different strengths, and keeping the ventilators closed all night, we find the following most satisfactory, harmless to the plants, death to the aphides and easy to apply:
Water, one pint.
Sulphuric acid, one pint.
Cyanide of potash, two and one-half ounces.
The above quantities for 1,500 cubic feet of air space in your house. And keep your house tightly closed all night.
Violet House Showing Arrangements for Fumigating with Hydrocyanic Acid Gas Recommended by the Department of Agriculture.
Mix the acid and water in 1-gallon butter jars, place as many jars as you need along on the paths of house, as equally divided as you can, and when all are in place walk along and drop the little parcel of cyanide into each jar; you can take your time. This is sure death to the little white fly so troublesome of late, and also to the aphis peculiar to the violet. Don't attempt to double up in quantity to save labor.
As compared with tobacco smoke it is quite expensive and some trouble to apply, but if it saves a crop of violets from the ravages of that minute fly that punctures the leaf, laying an egg which destroys the tissue of the leaf and produces what we call curl leaf, it is certainly worth ten times the cost and labor. It is applied principally to destroy the almost invisible insects so injurious to violets, but while doing that it utterly destroys greenfly, red spider, centipedes and all else that breathes. It leaves no objectionable odor.
Have the jar in which you generate the gas four times as large as the mixture of water and acid, and when purchasing the cyanide of potash have each package of two and one-half ounces well wrapped in double paper.