Gastric acid
The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
Jesse Francis McClendon
Jesse Francis McClendon (December 21, 1880 – November 22, 1976) was an American chemist, zoologist, and physiologist known for the first pH measurement of human stomach "in situ".