4. Employ only sufficient water to prevent the matter operated on from burning, and the product from being contaminated with empyreuma.
5. For substances whose oil is heavier than water, saturate or nearly saturate the water in the still with common salt, to raise the boiling point, and thus to enable the vapour to carry over more oil.
6. Employ, when possible, water which has been already distilled from off the same substances, and has thus become saturated with oil.
7. For oils naturally fluid, keep the water in the refrigerator cool; but for those oils which easily become solid, preserve it at 80° to 90° Fahr.(?)
To the above may be added—
8. Collect the oil as soon as possible after it separates from the water with which it passes over, and in its subsequent treatment keep it, as much as possible, from free contact with the air.
Dr Ure remarks, “The narrower and taller the alembic is, within certain limits, the greater will be the proportion of oil, relative to that of the aromatic water, from like proportions of aqueous and vegetable matter employed.” “Some place the plants in baskets, and suspend these immediately over the bottom of the still, under the water, or above its surface in the steam; but the best mode, in my opinion, is to stuff an upright cylinder full of the plants and drive down through them steam of any desired force, its tension and its temperature being further regulated by the size of the outlet-orifice leading to the condenser. The cylinder should be made of strong copper, tinned inside, and encased in
the worst conducting species of wood, such as soft deal or sycamore.”
The newly distilled oils may be separated from adhering water, which frequently renders them partially opaque or ‘cloudy,’ by repose in a temperature between 60° and 70° Fahr., and subsequent decantation; but to render them quite dry (anhydrous), it is necessary to let them stand over some fragments of fused chloride of calcium. This is not, however, required with the commercial oils.
The rectification of the volatile oils is commonly performed without water, by the careful application of a heat just sufficient to make them flow over pretty rapidly, so that they may be kept heated for as short a time as possible. One half, or at most two thirds only, is drawn off, that left in the retort being usually mixed with raw oil intended to be sold in that state. This method often leads to much loss and disappointment, and we have known more than one rather dangerous explosion result from its use. A better plan is to rectify the oil from strong brine, and then to separate any adhering water, either by repose or chloride of calcium.