Invoice from Arnold O. Beckman to W. E. Baier
for developing and calibrating McLeod gauges and glass electrodes -- components involved in the early Beckman pH meter.
Arnold Beckman invented his first pH meter in 1934…
These calibrations and the diagram were done by W. E. Baier, Research Manager of the California Fruit Growers' Exchange. The McLeod Gauge measures very low pressures of gasses. Its presence in this collection indicates…