Digestion in the sense of preparing extracts, essences or tinctures, means the exposing of the drugs with the extractive liquid to a gentle and continuous heat.

On the small scale the most convenient digesters are thin glass flasks, and the most convenient source of heat is the sand bath.

Fig. 405.   Condenser to Still, Fig. 404

Fig. 405. - Condenser to Still, Fig. 404.

Fig. 406.   Digesting Apparatus

Fig. 406. - Digesting Apparatus.

Digestion is often performed to soften and otherwise modify bodies that are to be distilled.

On the large scale either one of the steam-jacketted stills already described, (Figs. 402 and 404), may be employed, or, siill better, an apparatus, as represented by the annexed engravings, Figs. 406 and 407.

This apparatus consists of a cylinder, wherein the substances to be extracted are pressed between two perforated plates. After the apparatus is prepared the extracting liquid is poured in, filling the space a, and all openings are shut. Steam enters into the jacket, and digestion is carried on as desired; by means of the screws c the substances are pressed between the plates. At h the liquid can be drawn off, or if distillation is preferred, the stop cock is opened, allowing the vapors to be led over to the condenser C.

Maceration is called the steeping of a substance in cold water, for the purpose of extracting the portion soluble in that menstruum. The word is also frequently applied to the infusion of organic matters in alcohol or ether, or in water. The preparation of tinctures is carried on by maceration. In this regard we extract from the National Dispensatory the following directions:

Fig. 407.   Digesting and Distilling Apparatus

Fig. 407. - Digesting and Distilling Apparatus.

"The menstrua employed in the preparation of tinctures are alcohols of different strengths, spirit of ether or spirit of nitrous ether, and aromatic spirit of ammonia or ammoniated alcohol. According to the menstruum employed, tinctures are distinguished as ammoniated, ethereal, and alcoholic, and that class of tinctures, in the preparation of which diluted alcohol or a still weaker spirit has been used, is sometimes designated as hydro-alcoholic. By far the greatest number of tinctures are made with an alcoholic menstruum.