This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
See that Cape Jasmines are free from insects, or the beauty of the plants is spoiled; this is one of the plants, that if there is a bug, scale, or red spider in the house it is sure to find it out. A ready plan to clean these plants when at rest, is to mix up a strong dose of whale oil soap, about one ounce to a gallon of water and add about a large tea-spoonful of kerosene to the gallon, and dip the plants in the mixture; work the shoots well about in the mixture to wet every part and shake off or lay on their sides to drain for one hour, and if thoroughly done, there will not be an insect left alive, and the plants will not be injured; if there are many plants to dip, it will be necessary to add a portion more kerosene, as the oil floats on the water, and is skimmed off by the plants; of coarse care is required not to use extra quantity of kerosene, or it will injure the plants, and it is not safe to use it at all on many plants; but it is certain death to all insects. After the plants have drained for an hour, wash them well with clean water and the foliage will appear as if fresh varnished; this mixture must not be used when foliage is young and tender, but if thoroughly cleaned in the winter, it is seldom required at any other time.