ANALYTICAL CHEMISTRY
1056 One-ounce glass-stoppered bottles have been found convenient in distributions employing 10-ml. phases. Considerable time and effort may be saved by employing a shaking machine, such as a Fisher-Kahn shaker, to mix the solutions. While a transfer is being made (about 1minute), the bottle into which the previous transfer was made can be equilibrated by mechanical shaking. By this means an eight-plate distribution can be carried out in about 1 hour and a twenty-plate distribution in 6 hours, exclusive of the time necessary for analysis of the substance in the bottles. Craig et al. point out that a manual eight-plate distribution can be achieved without much trouble and recommend such a distribution for preliminary investigations. The present apparatus has an advantage over separatory funnels in that satisfactory results may be obtained with smaller volumes of liquid and contamination with stopcock grease is avoided; the distribution is more accurate and it can be carried out more rapidly than with separatory funnels if a shaking machine is employed. Where emulsions are encountered, the distribution may be carried out in stoppered centrifuge tubes and tubes centrifuged to separate the layers. Acids, such as hydrochloric, which attack stainless steel, may be employed in this setup. The bottles should be kept closed when liquid is not being added or withdrawn, as loss of solvents by evaporation may introduce an error.
Use of Sintered-Glass Disk in Preparation of Radioactive Precipitates. John J. Pinajian’ and John >I. Crossq2Brookhaven National Laboratory, Gpton, L. I., N. Y. VARIETY of devices and procedures
A for the mounting of radioactive
samples for activity measurements have been described (1-14). The authors have devised a convenient apparatus (Figures 1 and 2) for collecting fairly large samples of radioactive precipitates in a reproducible manner. The precipitate is filtered, washed, dried, and subsequently counted on a modified sinteredglass filtering disk. Several 22-mm. stock sintered-glass (F) crucibles were ground down so that a portion of the sintered glass was removed, leaving approximately 1.5 mm. as the thickness of the disk. The bottoms were ground so that the total height was exactly 6.7 mm. Glass rings 15.5 mm. in inside diameter and 1.1mm. thick were ground out from the central portion of a glass tube. The ring was ce-
mented on the top surface of the crucible with Sauereisen InsaLute adhesive cement No. 1. The unit was clamped together and treated in an oven. The ring, thus situat,ed, covered that portion of the sintered glass which was fused with the side wall of the crucible. A chimney was made of the same piece of glass tubing, with the lower edge ground so that a water seal might be made. Two glass hooks were drawn out on the chimney. The two units rested on the ground surface of a glass tube fitted with a T 24/40 joint, allowing the entire assembly to rest in a suction flask. Glass hooks were placed on the base so that rubber bands could be used to lock the assembly together. The filtering unit was used to determine the minimum “infinite” thickness of mercuric oxide labeled with Hgws-that is, such a thickness that a further increase in thickness would not result in a change in electron counting rate. Hg*O was precipitated and a quantity well in excess of that required for a sample of infinite thickness was collected in a filtering unit. The precipitate was washed with water, alcohol, and ether and then air-dried for several minutes. The disk with the precipitate was placed in a desiccator and dried to constant weight. A count was made and the unit reassembled. Ether was added and the precipitate stirred to form a slurry. A portion was siphoned off and the suction applied to remove the ethef. The precipitate was air dried, placed in a desiccator, dried to constant weight, and then counted. The results of several such manipulations were plotted and the minimum infinite thickness was found to be Figure 2. Complete 79.5 mg. of mercuric oxide Assembly per sq. em. These results were reproducible. The disks were easily cleaned by rinsing with dilute acetic acid and were checked for background readings. An aluminum card type holder with a groove to hold the disk was used to support the sample on a shelf below the mica-window Geiger-Muller tube. LITERATURE CITED
(1) Abers, E. L., Nucleonics, 3, No. 4, 43 (1948). (2) Armstrong, W. D., and Schubert, J., ANAL.CHEM.,20, 270 (1948).
(3) Burtt, B., personal communication. (4) Calvin, M., et al., “Isotopic Carbon,” New York, John Wiley &
Sons, 1949. Friedlander, G., and Kennedy, J. W.,“Introduction to Radio Chemistry,” New York, John Wiley & Sons, 1949. (6) Henriques, F. C., Jr., et al., IKD.ENG.CHEM.,ANAL.ED.,18, 349 (5)
(1946).
(7) Henriques, F. C., Jr., and hlargnetti, O., Ibid., 18,415 (1946). (8) Kamen, &I. D., “Radioactive Tracers in Biology,” New York,
Academic Press, 1948. Kohman, T. P., ANAL. CHEM.,21, 352 (1949). (10) SlacKenaie, A . J., and Dean, L. -A,, Ibid.,20, 559 (1948). (11) Rliller, W. W., personal communication. (12) Roberts, J. D., Holroyd, C. W., and Fugitt, C. H., ANAL.CHEM., (9)
Figure 1. Sintered-Glass Counting Disk with Base and Chimney
1 Present address, Graduate School of Pharmacy, Purdue University, West Lafayette, Ind. 2 Rutgers University College of Pharmacy, Sewark, N. J.
20,905 (1948).
(13) Sacks, J , Brookhaven Katl. Lab., BNL T-4 (1948). (14) Steele, R., and Sfortunato, T., Brookhaven Natl. Lab., BNL T-6 (Feb. 2 5 , 1949). F o r k supported in part by a grant from the Rutgers University Research Council end carried out a t Brookhaven National Laboratory.
