When oil has been kept for a long period it loses many of its impurities, and when buying it always enquire as to the age, as the older it is the better.
With the aid of chemistry we are able to render oil siccative in a very short time. The process need not be entered into fully at present, but the most usual method is to heat it in the presence of various metallic oxydes.
The mere fact of boiling oil will to a certain extent make it siccative, but if boiled together with some litharge it will become more siccative still, while similar treatment with oxide of manganese will impart a high degree of siccativity to the oil.
The oils in which oxygen is most intimately combined, in which the admixture of metallic oxides dissolved therein is the most perfect, and which contain the smallest amount of moisture, are the only ones that should be used for the purpose of making varnish, as the success of the varnish depends chiefly on the quality of the oil in its composition.
The distinctive character of Essential Oils
