Experience, however, has shown that volatile oils prepared by this process possess a finer odor the shorter the time the flowers remain in contact with the fat. Piver has devised an apparatus which reduces the time of maceration to the shortest period possible. The kettle to the left, Fig. 16, supplies the fat heated to the proper temperature, which circulates slowly through the macerating tank, in which a constant temperature of 149° F. is maintained by means of a steam pipe. The macerating tank is divided into compartments, in which baskets containing the vegetable substance to be extracted are suspended. The basket on the left contains the substance which has passed through all the compartments; it is from time to time removed, filled with fresh substance, and then attached to the right, the other baskets being moved to the next compartment to the left. In this way the fresh substance has to traverse each compartment from right to left, while the fat flows slowly from left to right, and saturated with the perfume of the substance collects in the tank on the extreme right. [Illustration: FIG. 16.] Maceration is employed for the flowers of the orange (_citrus aurantum_), of the mock orange (_Philadelphus coronarius_), of the acacia (_acacia Farnesiana_), of the violet (_viola odorata_), of the mignonette (_réséda odorata_), etc. The process of _absorption_, or "_enfleurage_," as it is called by the French, is chiefly made use of for procuring the odoriferous principle of very delicate flowers, the delicious odor of which would be greatly modified, if not entirely spoiled, by the application of heat. The older apparatus employed for the purpose consists of a number of shallow wooden frames of about 15×18 inches, inclosing at half their depth a sheet of glass. The edges of the frame rise about an inch above each surface of the glass, and, being flat, the frames stand securely upon one another, forming often considerable stacks. These frames are called "_chassis_," those just described being termed "_chassis aux vitres_," or "_chassis aux pomades_," to distinguish them from a different form, which is used where oil has to be submitted to the process of absorption. The process in the case of pomade is as follows: Each sheet of glass is uniformly coated with a thin layer of purified grease, care being taken that the grease does not come in contact with the woodwork of the frames. The flowers are then thinly sprinkled, or rather laid, one by one, upon the surface of the fat, where they are allowed to remain one or two days, when they are removed and replaced by fresh ones. The operation is thus continued for twenty-five or thirty days, until the fat is saturated with aroma. The frames charged with fat and flowers are stacked one upon the other, forming, in fact, a number of little rectangular chambers.