Search

The effect of hydrostatic pressures as high as 1,700 atm at 25 C on the heat and radiation resistance of Bacillus pumilusspores was studied. Phosphate-buffered spores were more sensitive to compression than spores suspended in distilled water. Measurements of the turbidity of suspensions, the viability, refractility, stainability, dry weight, and respiratory activity of spores, and calcium and dipicolinic acid release were made for different pressures and times. Initiation of germination occurred at pressures exceeding 500 atm and was the prerequisite for inactivation by compression. The rate of initiation increased with increasing pressure at constant temperature. This result is interpreted as a net decrease in the volume of the system during initiation as a result of increased solvation of the spore components.

The kinetics of initiation of germination and inactivation by hydrostatic pressure of phosphate-buffered Bacillus pumilusspores is shown to be a consecutive first-order process at 25 C. The effect of increasing pressure at constant temperature was studied, and rate constants were derived by using the criteria of heat resistance, refractility, and stainability. The calculated volume change of activation (ΔV‡) was −139 ± 6 cm3/mole for loss of heat resistance, −158 ± 8 cm3/mole for the loss of refractility, and −153 ± 4 cm3/mole for the change in permeability to dilute stains for the pressure range 800 to 1,010 atm at 25 C. It is suggested that the spore exists as a Donnan phase and that pressure triggers germination by influencing the equilibrium.

SEVERAL spectroscopic studios have recently been made of the light emitted from gases submitted to an intense shock wave1–3, but little information is available about the emission from air and other permanent gases. The very high temperatures available make the shock tube a convenient device for study of spectra of astrophysical interest, and a knowledge of the spectrum of air is necessary in any consideration of its high-temperature emissivity which may be required for problems of supersonic flight at high altitude. We have studied emission from air, nitrogen, oxygen, carbon monoxide and carbon dioxide or mixtures of these with argon.

IN a recent communication1, details were given of some unknown absorption features occurring during the flash photolysis of lead tetramethyl. While continuing this work, exposures have been obtained in which the most intense band at 3196 A. is apparently resolved into a series of Q-like heads. The satellite band at 3096 A. is also characterized by a central strong line-like feature and this also could be attributed to a Q head. There is no doubt that the bands 3196 A. and 3096 A. are related, since they disappear with the same life-time, which does not appear to exceed the duration of the photolysis flash. Moreover, in repeating the experiments on the flash photolysis of lead tetramethyl-d12an unmistakable shift of the 3096 A. band occurs. This band is considerably displaced towards the red while the 3196 A. band moves slightly towards the violet. The wave-numbers of all the features observed are given in Table 1. Fig. 1 is a microphotometer trace, which compares the spectra obtained in the photolysis of deuterated and undeuterated lead tetramethyl with the continuum produced by the source flash.

THE sodium-line reversal method of measuring temperature, commonly used for flames1, has been adapted to a study of the temperature distribution behind shock waves in a conventional shock tube. In the short times available, visual or photographic methods are impracticable but, with a photomultiplier and oscillograph, time-resolved records can be made. Using a direct-current ‘Pointolite’ lamp as background, we have measured temperatures in the range 2,000–2,900° K. for shocks through air, nitrogen and oxygen. By studying the records at various background temperatures, the temperature of the shock-heated gases could be determined within about ± 20°, or better than 1 per cent. An extension to higher temperatures appears possible by using arc sources as background.

THE flash photolysis technique1has been used to examine the photochemical decomposition of lead tetramethyl. At an energy of 2,500 joules (50 µF.; 10 kV.) the decomposition of lead tetramethyl at pressures up to 12 mm. mercury was shown to be largely complete in 1.2 m.sec. after the initial light flash; this was the time for the reaction vessel to become opaque to light due to the deposition of a lead film. The contents of the quartz reaction vessel (volume 500 cm.3, surface/volume = 1.6) were examined in this interval by passing a second light flash through the length (1 metre) of the vessel into a large Littrow (Hilger E1) spectrograph using a slit width of 0.02 mm.

A letter to the editor is presented regarding the Program Effects Generator which was launched at "Film '69."