ANALYTICAL CHEMISTRY
1802 with glass wool, as the manufacturer recommends, and the temperature of the system did not vary more than 2" C, the zero balance was easily maintained. While accuracy within 27, of the standard iodometric method was obtained in the concentration range of 0.5 to 1.6 mmoles of ozone per liter, there seems to be no reason why streams of at least slightly higher ozone concentrations cannot be analyzed similarly. PROCEDURE
A Gow-Mac four-filament thermal conductivity unit, Model RCT, with a 6-volt battery for power was employed. Through both arms of the cell dry oxygen was passed. The rate through each arm was not critical, but it Tyas essential that it vary not more than about 10% throughout the preparation and subsequent use of the calibration curve. In these experiments, the oxygen flow through one arm was 1.0 liter per minute; through the other, also connected to the ozonizer, 0.6 liter per minute. The cell filament was adjusted to its operating value, 138 ma., and the oxygen flow started. ilfter thermal equilibrium had been attained (about 1 hour), the unit was balanced by means of the zero balancing potentiometer on the cell control unit. The ozonizer, a ITelsbach Model T-23 generator, was then started, its voltage adjusted, and the ozonized stream passed through one arm of the cell, also at a rate of 0.6 liter per minute. The ozone concentration of the stream reached a constant value in 3 to 5 minutes, a t which time the cell voltage was measured to within izO.05 mv. with a Rubicon potentiometer. Generally, 2 to 3 minutes n-ere required for the conductivity cell to equilibrate. The ozone content of the gas was determined iodometrically (1).
7.00
6.00
5.00 u)
5
9i 4.00 2
I
3.00
2.00 .20
.40 .60 SO 1.00 1.20 1.40 1.60 1.80 MILLIMOLES OZONE PER LITER
Figure 1. Relationship between ozone concentration and millivolts
The ozone concentration was then increased to the next desired value; the range investigated was 0.5 to 1.6 mmoles of ozone per liter of gas. The cell retained its zero balance for the entire working day, and therefore the system did not have to be purged occasionally. A t the end of the third day, however, the values obtained varied within 5 % of the iodometric values, and the system was recalibrated. The voltage concentration data for the conditions employed in the laboratory are presented graphically in Figure 1. LITERATURE CITED (1)
Birdsall, C., Jenkins, A., Spadinger, E . , ANAL.CHEM.24, 662
(1952). (2) Kiffer, A., Dowell, L., Ibid., 24, 1796 (1952). (3) Pring, J., Westrip, G., Nature 170, 530 (1952). (4) Stair, R., Bagg, T., Johnston, R., J. Research Natl. Bur. Standards 52, 133 (1954).
Puriflcation of Di-2-naphthylthiocarbazone Donald M. Hubbard, Kettering Laboratory, Department of Preventive Medicine and Industrial Health, College of Medicine, University of Cincinnati, Cincinnati, Ohio
I-2-naphthylthiocarbaeone (2-naphthylazothionoformicacid)
D was originally synthesized by Suprunovich (6) and later
in this laboratory by Hubbard and Scott ( 4 ) . It has become an exceedingly useful compound for the quantitative determination of mercury in biological material ( 1 , 3, 6). The compound used for this type of analysis must be very pure, showing a molecular extinction coefficient of approximately 42,000 a t a wave length of 645 mp, when chloroform is used as the solvent. In order to obtain this purity it is necessary to purify twice, as described by Hubbard and Scott ( 4 ) . This purification process is tedious and the yield obtained for the final product is low. Cooper and Kofron have published a sound and usable method of purification ( 2 ) ,but a t present the authors are using a method which they feel is much more practical and very easy t o manipulate. The refined compound obtained by the latter method meets the requirements for purity as given above. Procedure. Place 0.5 gram of the di-2-naphthylthiocarbazone to be purified in a 100-ml. standard Griffin low-form beaker of Pyrex brand chemical glass S o . 774 with pour-out. Dissolve in 30 ml. of reconditioned chloroform, mixing with a glass stirring rod to effect solution at a low temperature on the hot plate. Allow the chloroform solution to cool to room temperature and then transfer it to a round-bottomed, short ring-neck, Pyrex brand boiling flask, capacity 50 ml., equipped with a T joint No. 19/38. Place the flask directly on the T 19/38 joint of a rotating vacuumtype evaporator mounting at an angle of about 30" from horizontal. Grease the stainless steel 7 joint of the evaporator with a small amount of high vacuum silicone lubricant. Connect the side arm of the evaporator, which is a T 12/30 joint (for use with glass connections if desired), directly to a suitable vacuum supply. A water aspirator is satisfactory, as no trap is required. A three-way stopcock may be inserted in the vacuum line. Turn on the vacuum and rotate the flask and contents, utilizing the built-in electric motor, for 30 minutes at 60 r.p.m. Release the vacuum and remove the flask. The remaining volume will be approximately 5 ml. Add 25 ml. of 200 proof ethyl alcohol, mix well by shaking, scrape the inside walls with a suitable glass stirring rod (slightly bent and flattened at the base) in order to remove particles that may adhere to the inside walls, and immediately immerse the flask and contents in a bath of acetone and dry ice for 10 minutes. Filter, using a Buchner porcelain funnel, and catch the precipitate on a No. 2 Whatman filter paper, 4.25 cm. in diameter. Rinse the flask with 10 ml. of 200 proof alcohol, again cool the flask and contents in the acetonedry ice bath, and finally wash the precipitate with the alcohol. Remove the filter paper and contents to a watch glass, add to it any precipitate that adheres to the sides of the funnel, allow the compound t o dry in the air, and weigh. The yield from 0.5 gram of the original compound should be approximately 0.3 gram. Reconditioned Chloroform. Place 1 liter of chloroform, redistilled from a borosilicate glass still, in a %liter glass-stoppered borosilicate glass separatory funnel. Dissolve approximately 10 grams of hydroxylamine hydrochloride in 50 ml. of distilled water and make alkaline to phenol red indicator by the addition of reagent grade ammonium hydroxide. Add this solution to the chloroform and shake well. Allow the aqueous layer to separate and filter the chloroform through a fluted filter paper into a brown glass-stoppered bottle containing 20 ml. of absolute ethyl alcohol. Shake well and store in a refrigerator. LITERATURE CITED (1) Cholak, J., Hubbard, D. M.,IND.ENG.CHEM., ANAL.ED. 18, 149 (1946). (2) Cooper, 5. S., Kofron, V. K., ANAL.CHEM.21, 1135 (1949). (3) Hubbard, D. M., IND.EXG.CHEM., A N ~ LED. . 12, 768 (1940). (4) Hubbard, D. M., Scott, E . W., J . Am. Chem. SOC.65, 2390 (1943). (5) Suprunovich, I. B., J . Gen. Chem. (U.S.S.R.) 8 , 839-43 (1938). (6) Warkany, J., Hubbard, D. XI., Lancet 254, 849 (1948).
