It is known that tin percolators are, unfortunately, largely used, but they are in most instances objectionable, not only because they are not as nice and durable as glass, but because they are acted upon by many drugs. Tin is usually sheet iron having a very thin coating of tin, which soon wears off, or is acted upon by the acids, nearly always present in vegetable drugs. The menstrua, whether they be aqueous or alcoholic, will soon act upon the exposed iron surface, and if that menstrua is saturated with the vegetable acids, especially of tannic, which is present in nearly all drugs, the inky contamination cannot be prevented. When drugs containing a large percentage of tannic and other acids are extracted in tin percolators, this contamination is quite marked. Even the seams are rarely soldered air-tight, and loss by evaporation of menstruum and percolate cannot be avoided. Therefore, unless carefully and thickly coated tin percolators are employed, they are better abandoned altogether to guard against contamination.

Fig. 386.   Cylindrical Percolator

Fig. 386. - Cylindrical Percolator.

Fig. 387.  Tin Percolator arranged for Volatile Liquids

Fig. 387. -Tin Percolator arranged for Volatile Liquids.