Substitutes which do claim attention are wax and dammar gum, or paraffin wax, dissolved in turpentine. The colours must then be ground in turpentine and not in oil. Such a vehicle is very pleasant to work with, and gives good results; moreover, it permits alterations or corrections to be made by rubbing out with turpentine. Nevertheless, both the wax and the turpentine undergo oxidation to some extent, and are therefore not altogether free from the same objections as oils. But benzol, especially when carefully prepared, answers all the purposes of turpentine without undergoing oxidation. The only drawback that can be urged against benzol is its odour, which some people have an aversion to; but it really has very little smell, and it evaporates away completely in a very short time. A mixture of wax, dammar, and benzol forms an excellent vehicle. The wax may be replaced by paraffin wax with advantage. It is desirable to be able to ascertain whether the oil intended for use is, or is not, adulterated with non-drying oil. The distinction of non-drying oils is that they solidify when acted upon by peroxide of hydrogen, or by sub-nitrate of mercury--the oleic acid is concreted, and a substance called elaidin is formed. This does not take place with the drying oils. The oils used in paint making are chiefly-- Ground-nut. Hempseed. Kukui or candle-nut. Linseed. Menhaden. Poppy-seed. Tobacco-seed. Walnut. Wood or Tung. GROUND-NUT OIL.--The ground-nut or pea-nut (_Arachis hypogæa_) is very widely cultivated in the tropics for the sake of its oily seeds. In Java, the oil is extracted by drying the seeds in the sun, and then subjecting them to pressure. In European mills, the nuts are first cleaned, then decorticated and winnowed, by which the kernels are left perfectly clean. These are crushed like any other oil seed, and put into bags, which are introduced into cold presses; the expressed oil is refined by passing through filter-bags. The residual cake is ground very fine, and pressed under 3 tons to the inch, in the presence of steam-heat; this affords a second quantity of oil, inferior in quality to the cold pressed. The usual product is 1 gal. of oil from 1 bush. of nuts by the cold process, besides the extra yield by the hot pressing. In France, where the oil is most largely prepared, three expressions are adopted, as with some sorts of gingelly: the first gives about 18 per cent. of superfine oil, fit for alimentary purposes; the second, after moistening with cold water, affords 6 per cent. of a fine oil, suitable for lighting and for woollen-dressing; the third, after treating with hot water, yields 6 per cent. of _rabat_, or oil applicable only to soap-making. In India, the total mean yield is 37 per cent. at Pondicherry, and 43 in Madras.