This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
This is another means, or at least a link in the various methods of detecting fraudulent essential oils. The proper boiling-points we indicate hereafter for the respective oils employed by the carbonators. In applying the apparatus illustrated here, we must append the remark, that we propose the operation to be performed at a barometer stand of 760 mm. whatever the boiling point of the thermometer employed may be. This barometer stand is considered the air pressure exerted on the quicksilver in the barometer tube above the surface of the sea. When therefore this "boiling test" is executed, it must be borne in mind that the air-pressure on highly situated localities is less, the boiling point consequently lower. The proper barometer stand should be first ascertained and allowances for variations made accordingly.
We then use the illustrated apparatus, the thermometer used being graduated for instance above 300° C., each degree being divided again in tenths to allow an accurate determination. This thermometer is inserted by means of a tight-fitting perforated cork into a glass tube, suspended by a suitable support, so that it can be heated by an alcohol lamp. Into the glass tube pour some of the suspected oil, adjust the thermometer, suspending it a short distance from above the surface of the liquid, the thermometer not touching the latter. Into the perforated cork also adjust a bent glass tube as illustrated, to give way for rising vapors and preventing the explosion of the closed glass vessel. In order to ascertain the boiling point of the suspected oil, heat the porcelain dish beneath. The latter contains sand, the glass-tube being to some extent surrounded by the latter. A direct flame is able to burst inferior glass tubes. When bubbles arise from the liquid, the boiling point is reached. The flame then should be lowered and the indications on the thermometer noticed. The adulteration is the difference between the figures shown on the thermometer, and the figures of the standard boiling point of pure oil.