Dictionary.net

Is composed of equal parts of quicklime and potassa cum calce. In using it, it is made into a paste-Vicuna paste, (F.) Caustique de Vienne, Pate Caustique de Vienne--with spirits of wine, and is applied on the diseased part, previously circumscribed by a hole cut in a sticking plaster. To be left on from 10 to 20 minutes, according to the depth of the eschar required. Used in cases of lupous ulceration. By fusing the potass and lime, and raising the heat so as to cause ebullition, the caustic may be run into cylinders :-when it is called Caustique-Filhos, Caus'ticum Viennen'se fusum Filhos, from the name of the author of the process.