The same authority assures us, with regard to the actual nature of the _prima materia_, that it is one only and self-same thing, although it is a natural compound of certain substances from one root and of one kind, forming together one whole complete homogeneity. The substances that make up the philosophical compound differ less among themselves than sorrel water differs from lettuce water. Urbiger asserts that the true and real matter is only “a vapour impregnated with the metallic seed, yet undetermined, created by God Almighty, generated by the concurrence and influence of the astrums, contained in the bowels of the earth, as the matrix of all created things.” In conformity with this, one earlier writer, Sir George Ripley, describes the stone as the potential vapour of metals. It is normally invisible, but may be made to manifest as a clear water. So also Philalethes cries in his inspired way:--“Hear me, and I shall disclose the secret, which like a rose has been guarded by thorns, so that few in past times could pull the flower. There is a substance of a metalline species, which looks so cloudy that the universe will have nothing to do with it. Its visible form is vile; it defiles metalline bodies, and no one can readily imagine that the pearly drink of bright Phœbus should spring from thence. Its components are a most pure and tender mercury, a dry incarcerate sulphur, which binds it and restrains fluxation.... Know this subject, it is the sure basis of all our secrets.... To deal plainly, it is the child of Saturn, of mean price and great venom.... It is not malleable, though metalline. Its colour is sable with, with intermixed argent, which mark the sable field with veins of glittering argent.”[D] The poisonous nature of the stone is much insisted on by numerous philosophers. “Its substance and its vapour are indeed a poison which the philosophers should know how to change into an antidote by preparation and direction.”[E] No descriptions, supplied _ad infinitum_ by the numberless adepts who were moved by unselfish generosity to expound the arcana of alchemy, for the spiritual, intellectual, and physical enrichment of those who deserved initiation, expose the true nature of the _prima materia_, while the _vas philosophorum_ in which it is contained and digested is described in contradictory terms, and is by some writers declared a divine secret.