Vol. 16, No. 5
INDUSTRIAL AND ENGINEERING CHEMISTRY
346
All-Glass
M i d g e t lmpinger Unit
t
ENGINEERING UNIT, Division of Industrial Hygiene, National Institute of Health, U. S. Public Health Service,
Bethesda, M d .
I
NCREASED use of the midget impinger (2) for collerting various atmospheric contaminants has revealed the following disadvantagcs:
1. The rubber stopper deteriorates through contact with various acids, alkalies, and solvents used as collecting fluids. It is extreme1 difficult to clean the rubber stopper when slight deterioration [as begun. This may result in contamination of the sample. Certain solvents dissolve a color from the stopper, which interferes in colorimetric analysis. 2. The side arm of the impinger flask is sufficiently low to permit drawing over a portion of various alkalies and solvents used as collecting fluids. 3. When the stopper is placed in the flask, an annular groove is formed where the stopper contacts the flask. Air Contaminants may settle in this grbove and cause subsequent contamination when the sample is transferred in the field. To eliminate these disadvantages, an all-glass collecting unit (see d.agram), similar to the large impinger unit (I), has been designed and used satisfactorily during the past year. The allglass equipment can be cleaned thoroughly. The standard taper permits intcr:hanging of parts without readjusting the position of the impinging orifice, which was necessary in the earlier design. The side arm is 138 mm. above the bottom of the Bask, as compared to 103 mm. in the earlier design. This added height reduces the possibility of a draw-over when certain solvents and alkalies arz used as collecting fluids. A shoulder around the atandard taper stopper cover3 the groove formed between the stopper and the flask, and prevents the settling of dusty material in the groove where it may' contaminate the sample during transfer.
A
All dimmtlons in
For certain purposes, similar all-glass equipment has been designed with a fritted-glass bubbler replacing the impinging orifice. Thus, a single type of unit may be med over a wide range of collecting requirements. LITERATURE CITED
Greenburg, Leonard, and Bloomfield, J. J., Public Health Rem., 47, 654-75 (March 18, 1932). (2) Schrenk, H. H., and Feicht, F. L., U. S . Bur. Mines, I n f o r d i o n Circ. 7076 (June. 1939). (1)
Simple Titration Rack
E. C. C A N T I N O , Division of Plant Nutrition, University of California, Berkeley, Calif.
R
ECENT investigations in this laboratory have involved the use of various semimicrochemical methods of analysis. Such methods often require centrifugation of minute quantities of material in small conical centrifuge tubes, and subsequently a titrimetric determination of this material in the same vessel. However, adequate agitation during the titration is difficult in
such containers and the process becomes increasingly tedious when a number of determinations are necessary. I n order to obviate this difficulty and to provide a rapid method of analysis, a simple titration rack was designed as illustrated. The stand consists of a wooden base and frame which support a frosted-glass background. Eight brass spring clips are attached to the frame, so that centrifuge tub@ may e a d y be dipped firmly into position. The glass manifold which serves as an aerating device can then be manipulated into position by means of clamps b and b', attached to vertical wooden rods which in turn are s u p ported by the frame. The rate of air flow is regulated by the control valve, A . The small valve above each t u b e i s s u b s e q u e n t l y opencd when the contents are to be titrated. By moving the reagent bottle and attached buret, B , consecutively from one tube t o the next, a series of eight determinations can be rapidly completed. ACKNOWLEDGMENT
The author wishes to thank H. Wells for help with the construction of the apparatus.
