Does the use of a patented process by a third person constitute an infringement when the alleged infringer has substituted, in lieu of some unessential part of the patented process, a well-known mechanical equivalent."
Yes, under the doctrine of mechanical equivalents, the patentee is protected from colorable invasions of his patent under the guise of substitution of some part of his invention by some well known mechanical equivalent. It is an infringement of the patent, if the substitute performs the same function and was well known at the date of the patent as a proper substitute for the omitted ingredient. (Gsell v. Yap-Jue, G.R. No. L-4720, Jan. 19, 1909)