Thomas T. Mercer

Operating Characteristics of Some Compressed-Air Nebulizers

Abstract The outputs and mass median droplet diameters of useful aerosols and the effect of solvent evaporation on the concentration of nebulizer solutions have been measured for four nebulizers of designs which have been employed for inhalation studies. Outputs ranging from 2.3 to 30.4 microliters of solution per liter of jet air were observed, with corresponding mass median droplet diameters of 1.4 to 5.4 microns. For jet pressure drops of 2.5 to 30 psi, from 7 to 10 microliters of solvent (water), in excess of that associated with the aerosol, was carried away per liter of jet air. The effects of baffling and of augmenting the jet air with additional flow through a vent were also determined.

A Point-to-Plane Electrostatic Precipitator for Particle Size Sampling

Abstract A point-to-plane electrostatic precipitator of simple design is described. It was developed as a particle size sampling instrument for use with the electron microscope. The standard operating conditions as well as special design and technical points are described and illustrated. Tests of the instrument have been made using the thermal precipitator as a standard. These comparisons have indicated no important limitation of the point-to-plane precipitator as a particle size sampler. Other advantages and disadvantages of the instrument based on our experience are given. Most of these points are documented by photographs. None of the negative qualities of the sampler appear general or restrictive. Conversely, there are specific attributes which make the point-to-plane electrostatic precipitator a valuable, if not indispensable, tool in aerosol studies.

Charges on Droplets Produced by Atomization of Solutions

The charges on droplets produced by air-blast atomization were determined for 0.1%, 1.0%, and 10% concentration of sodium chloride-uranine solute in water. A parallel-plate mobility spectrometer was used to measure the mobility of residual solid particles, and simultaneous size distribution measurements made it possible to calculate the charge on the droplet from which the solid particle was derived. The relationship between the average number of electronic units of charge, |q¯| on a droplet and its diameter, D, |q¯| aD b where a and b are functions of the solute concentration. Droplet charges were not symmetrical with respect to polarity, an effect which was also related to concentration. The results are compared with those reported by others, and their practical significance is discussed.

Effect of Magnification on the Estimation of the Parameters of a Log-Normal Distribution

The effects of magnification on sample statistics calculated by maximum likelihood, class analysis, and probit analysis methods have been studied for log-normal distributions having standard deviations between 0.5 and 1.1 (geometric standard deviations between 1.65 and 3.00). A lower limit of observation has been assumed so that sample truncation occurs. Theoretical results for infinitely large samples and experimental results for samples of size 100, 200, 500, and 1000 covering ten levels of magnification are presented and compared. The results include estimates of the standard errors on the means and variances as calculated by the different methods.

SZOLD: Its Properties and Relationship to Other Distributions

Abstract SZOLD is a form of the three-parameter lognormal distribution. As originally defined, its normalization factor permits negative values of the distributed variable for some positively skewed distributions and for all negatively skewed distributions. Correct normalization factors are given here, and the degree of truncation is shown as a function of the distribution parameters.