Abstract
A simple, expedient, and accurate method of determining the efficiency of a filter is described. A test cloud comprised of lithium hydroxide particles with a mean particle size by weight of about 0.6 micron is blown into the test filter. The efficiency of the filter is estimated from the ratio between the amount of lithium contained in air samples before and after the filter. The method can be conveniently used for filters displaying up to 99.99% efficiency. The method requires, besides an atomizer for production of particles of the appropriate size and a flame photometer, the application of laboratory equipment normally present in a laboratory concerned with air-control problems.