A new electron gun has been built which features mechanical and optical simplicity. Theoretically, it can produce a focused spot having a radius smaller than 50 Å and provide 1000 times more intensity than a hot filament system having a similar final spot size. The increase in intensity is made possible by using a field emission electron source operating at a pressure of 10−9 Torr, which is provided (without baking) using commercially available pumps. The small spot is produced by using two properly shaped electrodes which accelerate and focus the electrons from the tip. It would take a hot filament gun and at least two additional lenses to replace this field emission gun when a spot radius less than 100 Å is required. Even then the brightness of the conventional source would be too low to make use of the small spot size obtained. The optical properties for the new gun were predicted on a computer and experimentally confirmed in a new scanning electron microscope. The aperture aberration coefficient was measured to be no more than a factor of two greater than the theoretical value of 1.5 cm. A spot radius of 250 Å has been measured, and this value is to be compared with the theoretical value of 150 Å. Although it was convenient to measure the spot directly only at a relatively large image distance (11.3 cm), calculations imply that the gun can provide a spot radius less than 25 Å when very small image distances are used. The gun can be used in pulsed operation because all optical properties are constant for a given voltage ratio so that application of the electrode voltages by means of a voltage divider provides automatic focusing for arbitrary changes in the applied voltage. The methods used to make and operate reliable high field emission tips are reviewed, and a technique is described for changing the required tip voltage to obtain a given emission current.

No abstract

No abstract

Evidence is presented which indicates that the bactericidal activity of quaternary ammonium salts increases with increased charge density on the nitrogen atom but that other factors such as increased bulk around the nitrogen may act to decrease this activity. Within the series of compounds tested activity reaches a maximum a t a carbon chain length of sixteen to eighteen, depending upon the test organism. Bactericidal activity generally appears to increase with decreased critical micelle concentration within the series of compounds tested.

Solubilities of saturated fatty acids in water reported by John and McBain (1) are one-fifth to one-tenth of those reported by Ralston and Hoerr (2). As a result of these discrepancies, it was decided to reopen the study.EXPERIMENTAL Preparation of Materials. The fatty acids used in this work were highly purified samples prepared by Mr. R. S. Sedgwick. Freezing points of the acids were as follows: octanoic, 16.63°; nonanoic, 12.52°; decanoic, 31.49°; hendecanoic, 28.59°; dodecanoic, 44.16°; tetradecanoic, 54.25°. Water with a conductivity of 1 micromho was used in making up all solutions.Procedure. Most of the determinations were made on fatty-acid solutions saturated by heating to 100°, shaking, then placing in a constant-temperature bath with a regulation range of ±0.05°. In several cases, saturation was also approached from a lower temperature, and in all such runs identical values were obtained. The minimum saturation time at the desired temperature was 16 hours. This time was checked in some cases by starting from an over-or under-saturated state, and was found to be adequate. During the saturation period, the solution was stirred by bubbling purified nitrogen through it. The nitrogen had previously been led through soda-lima and then water.To measure a volume of solution for analysis, a pipet of 149.4 cc. capacity was built into the constant-temperature bath in such a way that most of the path for transporting the solution from the saturation flask to the pipet was in the water-bath. This system was so arranged that the solution was exposed only to the purified-nitrogen atmosphere.The cell consisted of unplatinized platinum electrodes built into a 300-ec. round flask. The constant was approximately 0.