In entering upon the subject, it was stated to be essentially one requiring experience ; as a fitting conclusion, and a practical illustration of how experience is to be applied, three examplea may be given of analyses of mixtures which have recently come before the present writer.
I. A Sample of Lubricating-oil.—Very pale-yellow in colour, and smelling of paraffin-oil ; 0.5 grm. heated at 110° (230° F.) till constant lost 0.1 grm. = volatile paraffin 20 per cent. A larger portion heated till it ceased to lose weight, then saponified, and tested, gave no separation of mineral oil. The colour proved that there was no rosin-oil, and the liquid when acidulated threw up fatty acida which, on cooling, partly solidified : ergo suspected lard or neats'-foot. The remainder on the watch-glass, after volatilizing the paraffin, had, while hot, the faint odour of lard-oil, and, treated with barium polysulpliide, became almost colourless, and smelt slightly of sulphuretted hydrogen. A large quantity of the oil heated in a flat dish at 110° (230° F.) for some hours, and cooled to 38° (100° F.), had an "actual density" of 0.9077. Zinc chloride showed absence of olive-oil, there fore the report was :—Paraffin-oil, 20 per cent. ; lard-oil, 80 per cent.
II. A Sample intended to be sold as Salad-oil.—Colour yellow with a faint greenish tint. Heated, it smelt of fine olive-oil, but slightly more rancid. Tests proved no mineral oil, and colour forbade rosin-oil. Actual density, Barium polysulphide, colour remained golden. Zinc chloride, green at first, but developed a decided pale-brown. Sulphuric acid, no green tinge, but a pale reddish-brown. The tests show that it is not colza ; and some saponified, and the fatty acids dissolved in 4 parts alcohol, give no precipitate on diluting, therefore no ground-nut. The brown tinge with the zinc chloride could not have been produced by poppy, so that it is probably olive mixed with refined cotton. By density it would show about :—Olive-oil, 66 per cent. ; cotton-oil, 33 per cent., if this conclusion be right. Next tried a standard sample of olive, and one of refined cotton, by the sulphuric acid method, and then tried the sample, when the comparative elevations in temperature showed 35 per cent. of cotton. Taking, therefore, a common-sense view of the matter, the oil was considered to he s olive and cotton.