This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Sebum majus vulgare C. B. Aizoon & bar-bajovis 'quibusdam, Sempervivum tettorum Linn. Houseleek. or Sengreen: a plant with numerous, thick, stiff, fleshy, pointed leaves, lying over one another in form of a roundish cluster; in the middle of which rises a stiff stalk, covered with smaller leaves, divided at the top into several branches, bearing purplish flowers with twelve petala, which are followed by the same number of capsules full of small seeds. It is perennial and evergreen, grows on old walls and the tops of houses, and flowers in June.
The leaves of houseleek, of no remarkable smell, discover to the taste a mild subacid au-sterity: their expressed juice, of a pale yellow-ish hue when filtered, yields on infpiflation a deep yellow, tenacious, mucilaginous mass, con-siderably acidulous and acerb: from whence it may be presumed, that this herb has some claim to the refrigerant and restringent virtues that have been ascribed to it. It is observable that the filtered juice, on the addition of an equal quantity of rectified spirit of wine, forms a light white coagulum, like creme of fine pomatum, of a weak but penetrating taste: this, freed from the fluid part, and exposed to the air, almost totally exhales. From this experiment it is concluded by some that houseleek contains a volatile alkaline salt](a): but the juice coagulates in the same manner with volatile alkalies themselves, as also with fixt alkalies: acids produce no coagulation.