Branly was the first to investigate and describe in 1890 the fact that an electric spark at a distance had the power of changing loose aggregations of metallic powders from poor to good electric conductors, and he also found that in some cases the reverse action was produced.
The procedure consists in most cases in spraying the affected plants with poisonous solutions or emulsions, or in (lusting them with fungicidal or insecticidal powders, or applying the fumes of lethal gases.
For the composition of the numerous liquids and powders special works must be consulted, but the following principles apply generally.
The application of ordinary antiseptic powders to leaves inside which a Fungus, such as a Uredo or Ustilago, is growing can only result in failtire, and similarly if tobacco fumes, for instance, are applied when the insects concerned are hibernating in the ground beneath.
The water in a soap is rarely directly determined; when it is, the soap, in the form of shavings, is heated to 105° C. until the weight is constant, the loss giving the amount of ' " Soap powders " and " soap extracts " are powdered mixtures of soaps, soda ash or ordinary sodium carbonate.
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