Part I of this article presents results of an experimental study on gas-phase nucleation for three model solutes and their solvent, propylene glycol (PG), with variables being solute concentration and the nature of the solute substance. A single manifestation of an aerosol generator, which forms condensation aerosols by cooling of hot vapor issuing from an electrically heated, pumped capillary, is described and used for all experiments. The effects of solute concentration and solute type were studied for deoxycorticosterone (DOC), benzil (BZ), and phenyl salicylate (PhS). Suppression of homogeneous nucleation and occurrence of heterogeneous condensation of the solvent was observed at different solute concentrations for BZ, PhS, and DOC. The nature and concentration of the solute dissolved in the solvent was shown to determine the final particle size distribution of the condensed aerosol. In the case of the least volatile solute, DOC, solute aerosol and total aerosol size distributions were identical at low solute concentrations. A transitional concentration region then existed in which a bimodal solute aerosol was formed, followed at high concentrations by increasing separation of the solvent-dominated aerosol size distribution and that of the solute.In Part II of this article, the effect of DOC dissolution in different solvents was studied at fixed solute concentration. The effects of six glycol solvents-i.e., PG, ethylene glycol (EG), dipropylene glycol (DPG), diethylene glycol (DEG), triethylene glycol (TEG), and tetraethylene glycol (TetEG)-and three nonglycol solventsi.e., dimethyl sulfoxide (DMSO), formamide (FORM), and oleyl alcohol (OA)-were studied, as these affected the resultant aerosol sizes. Suppression of total aerosol mass median aerodynamic diameter (MMAD) was observed on dissolution of 0.5% w/w DOC in each solvent, although suppression occurred to different extents. It was shown that the boiling point or volatility of the solvent used to dissolve the less volatile DOC had an effect on the final particle We wish to express our appreciation to Chrysalis Technologies Incorporated for providing the equipment and funding for this study.Address correspondence to Michael Hindle, Aerosol Research Group, Department of Pharmaceutics, Box 980533, Virginia Commonwealth University, Richmond, VA 23298-0533. E-mail: mhindle@ hsc.vcu.edu size distribution of the condensed aerosol and whether the aerodynamic size distributions for the solute and the total aerosol were the same or different.

The time and heat flux required for the initiation of smoldering combustion in cellulosic fabrics depends on the properties of both the environment and the fabric. In the environment, there must be sufficient oxygen to support smoldering combustion and there must be sufficient heat to raise the temperature of the fabric to the point where combustion becomes self supporting. The critical factors for the cellulosic fabrics are the potassium and/or sodium ion content and the thermal characteristics of the fabric. A series of simple weave, raw cotton fabrics, commonly referred to as cotton ducks, and an upholstery fabric were examined. The requirements for the initiation of smoldering combustion were similar for both the ducks and the upholstery fabric. However, the situation for the upholstery fabric was complicated by the non-homogeneous distribution of ions in the material and spatial variations in fabric thickness and basis weight. Also, for fabrics with potassium and sodium ion contents in the range of approximately 1500 to 2500 ppm, there was an increased sensitivity to the environmental factors.

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Linear burn rates were determined for thin, cellulosic materials (papers and cotton fabrics) held in the horizontal plane by measuring the rate of radial increase of the circular burn pattern. Linear burn rates were determined for freely smoldering materials and for materials in contact with polyurethane foam. The linear burn rates of the freely smoldering materials were found to be inversely proportional to basis weight. This relationship held over basis weights from 0.8 to 24 oz/yd 2 . The linear burn rates of the materials in contact with polyurethane foam were also inversely proportional to basis weight and were reduced about 16% from the free smolder rate. The effect of potassium ion content was also examined. A minimum level of potassium, approximately 1300 ppm, was required for sustained smoldering combustion. Above this minimum level, the ion content did not have a significant effect on the linear burn rate.

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