For the accurate determination of the percentage of volatile oil a vegetable substance will yield, or to obtain the oil from very costly raw materials, the small glass apparatus, Fig. 2, is used. The flask _A_, with a capacity of up to 5 or 6 quarts, serves for a still. In the tube _t_, shaped like the neck of a bottle, is inserted by means of a cork, a funnel tube, _l_, reaching to the bottom of the flask. The neck of the flask passes into the cooling pipe, which lies in a so-called Liebig cooler. This consists of a wide-glass tube, _C_, into the lower end of which, at _h_, flows cold water from the reservoir _D_, displacing the heated water at _g_. The lower end of the cooling pipe is connected with the neck-shaped tube _v_, under which stands the vessel for the reception of the distillate. To prevent the cracking of the flask, which might readily happen with the use of direct heat, it is placed in a vessel filled with sand or water. [Illustration: FIG. 3.] A very good small apparatus for the distillation of volatile oil is shown in Fig. 3. It is known as a siphon still. It consists of a double-walled boiler, surmounted by a still-head, which is provided with a mechanism for keeping the contents of the boiler in motion. This stirring apparatus consists of a perpendicular shaft, bearing a frame work of iron, curved so as to correspond to the interior shape of the still, and on the outside carrying a chain which scrapes over the inner surface of the still while the stirrer is being turned. This may be done either by hand or by steam. The still having been charged with the material to be extracted, is filled up with water to within a few inches of the top of the body of the still, and the latter is heated by admitting steam. The vapors arising are conducted to a cooler situated at a higher level than the still itself, and the condensed liquid is collected in a receiver, where the oil and water separate. This receiver is provided with two faucets, one near the top and the other near the bottom. If the oil passing over is heavier than water, the excess of the latter is removed by the upper faucet; if the oil swims on the water, the lower faucet is regulated so as to allow the water to escape in about the same ratio as it enters the receiver. In either case the condensed water is made to run back into the still, and the loss of oil is, therefore, greatly reduced. Sometimes a single-walled still is used, and distillation carried on with direct steam. This method is, however, not suitable where the presence of water is necessary, for instance, in the production of oil of bitter almonds.