A4NAL1TICAL EDITION
FEBRUARY 15, 1940
Test Runs The cryostat has been held a t various temperatures from f20' to -28" C. for varying periods, in one instance for 2 weeks of continuous operation. Various data and results of calculations for the run a t -28.11 O C. are presented in Tables I and 11. The values in Table I are the extremes observed. not necessarily a t the same time, and in all probability do not represent the maximum differences. Table I s h o m that the variation in the total heat leak was of somewhat greater magnitude than the mean intermittent energy input, and that the variation in the modulated continuous energy input was nearly twice that of the mean intermittent energy input. This forcibly illustrates the neces4 t y of a modulator in such a control. The data of Table I1 indicate that the control functions exceptionally well over long periods of time, in spite of external fluctuations, and that high thermoregulator stability has been secured. At the observational period of 48 hours, the data plotted in Figure 4 mere obtained. I t a later period, with the bath operating a t -11.37' C., after the stirring had been improved and with a somewhat more sensitive thermoregulator (owing t o more thorough methods of filling and a sharper tungsten contact mire), the data of Figure 5 were gathered. Without the modulator, the control system functions to about = t O . l ' with no manual adjustment; if occasional manual adjustment is performed, 10.03O can be readily realized during the time that the bath temperature is under direct
117
obervation. A compressor of the size described here is capable of holding the h t h a t --&Oc' C.: with a larger machine, undoubtedly, lon-er temperatures may be attained. A simpler electrical circuit can be designed, employing a circular resistance in place of the Variac and utilizing a mechanical relay in the Thyratron plate circuit to control the direction of rotation of the Telechron, thus dispensing with the 45-electron tube. Such a system as the author has developed could be applied to a much larger bath, since a t -18" C. the compressor is doing but approximately half the work for which i t is rated.
Acknowledgment This apparatus was developed in the laboratory of hrt,hur B. Lamb, with whom the author has had many discussions concerning the design, and whom he wishes t,o thank for permission t,o publish this description.
Literature Cited (1) Beattie, Proc. Am. Aced. Arts Sci., 69, 389 (1934). ( 2 ) Benedict, Rev. Sci. Instruments, 8, 252 (1937).
(3) Buffington and Fleischer, IND. ESG. CHEJI., 23, 1290 (1931). (4) Gilkey, Gerard, and Bixler, Ibid., 23, 364 (1931). (5) Gucker, Pickard, and Planck, J . Am. (:hem. SOC.,61, 459 (1939). (6) Kistiakowsky, Romeyn, Ruhoff, Smith, and T'aughan. I hid., 57, 65 (1935). (7) Roper, Ibid., 60, 866 (1938). (8) Ibid., 6 0 , 1693 (1938).
A Nebulizer for Inhalation Experiments ROLLAND J. 3141N,IIedical College of Virginia, Richmond, \'a.
R
E C E S T L Y the author had need of a nebulizer to prodnce a fine miPt of various solutions f o r inhalation by experimental animals. Several types of nebulizers available vommerciallv or reported in the literature were either tried or conside-red, g u t t h e y spattered droplets, were difficwlt to make, or were not compact. Since the concentration of the T-apor was to C be determined by measuring the air blown through per unit of time and calculating the amount of liquid carried over by the difference bet w e e n p r i m a r y a n d final weights, i t was necessary to obtain a nebulizer which did riot spatter, and which mould produce a mist that did not readily settle out. C o n s e q u e n t 1y the glass nebulizer supplied by Parke, Davis and Company was modified as shown in Figure 1 (made by E. llachlett & Son, 220 East 23rd St., Kew York, N. Y .). This has proved very satisfactory for the types of solutions used, in not spattering and in producing a stable smokelike mist. FIGURE 1
Lip A prevents fluid collecting in the outlet tube from being blown out in droplets. The slope of tube B causes such drops to run back Bend C prevents drops from being blown out. The bores of the' tips of tubes D and E are approximately 0.7 mm, in internal diameter. The total height is 19 cm. The lower bulb holds 15 cc. of fluid. and could essilv be made larger in diameter to hold more. With :t pressure of 5"69 mm. of mercury (11 pounds per square inch), 8 liters of air per minute pass through. The nebulizer uses from 4.5 to 8 co. per hour of kerosene solution, depending upon the concentration of the solute and the temperature. .4n -4llied rotary air blast pump without a pressure tank is used. h large glass tube filled with glass wool is interposed between pump and nebulizer to act as an oil trap. The output of air from the atomizer, Kith a fixed setting of the stopcocks on the pump, is measured occasionally by a wet gas meter to ensure constant output. This apparatus has proved satisfactory for such solutions as an organic thiocyanate in refined kerosene. Yo concentration of this solution occurred in the nebulizer, :ts proved by chemical analysis. When used for hygroscopic substances like propylene and diethylene glycol and glycerol, the moisture in the air dissolves in the solvent, making it impossible to determine horn much solvent has passed over by merely weighing the tube. I n these cases chemical analyses of the residue as well as weights are required. If a source of air of constant humidity is available, the concentration of material in equilibrium with this humidity can be determined, and this mixture used without necessity for analyses.
Acknowledgment The author is indebted to Parke, Davis arid Company for permission toreport on this modification of their nebulizer,
