potential is applied for each reading, and all bulbs of the same manufacture are used to ensure reproducible results. The results of two calibration runs are shown in Figure 2. The filaments of A/C No. 63 bulbs were used at an applied potential of 10 V and a gas flow rate of 1.1 l./min. The filament assembly is connected to the recirculating system via double end shut off quick-connects. The assembly is removed from the gas stream after each performance test and replaced with a jumper tube. The filament is replaced and the assembly purged with nitrogen before returning it to the recirculating system. Pressure Control. The fully automatic pressure control system is based on a differential switch-gauge having both high and low pressure limit switches. (Photohelic Series 3000, F. W. Dwyer Manufacturing Co., Inc., Michigan City, Ind.). The box pressure is maintained within the desired range (typically between 0.2 in. HzO and 0.6 in. above atmospheric pressure) as follows: The recirculating pump is discharged to the atmosphere through solenoid valve B when an over-pressure is created (as when the hands are inserted into the gloves). Additional gas is supplied from the cylinder through solenoid valve A when an under-pressure is created (when the hands are withdrawn from the gloves and when the entry port is being back-filled or purged). An iso-
lating seal consisting of a 2.5- X 0.002-in. polyethylene bag in a 2- X 12-in. Lucite tube is used to protect the Photohelic gauge from corrosion (8). RESULTS
The dry box was initially purged without recirculation to reduce the oxygen concentration to -1000 ppm. This procedure lengthens the life of the BTS-Catalyst before regeneration is needed and also reduces the heating of the catalyst. Water and oxygen content were measured as a function of box throughputs. Under the conditions employed (0.19 box throughput/hour using a 25-mm X 60-cm catalyst column and a 25-mm X 45-cm molecular sieve column) impurity concentrations were reduced to
