?
ANALYTICAL EDITION
January 15, 1943
made by taking advantage of its natural radioactivity, Obviously, the type of equipment used in making these analyses may be applied with advantage for work with other radioisotopes, -whether natural or artificial. The size and design of the tubes employed naturally are not restricted to those d e scribed here, but may be altered to meet particular conditions. Once the apparatus has been set up, a determination requires 10 minutes to 2 or 3 hours, depending on the sensitivity of the counter, the potassium concentration, and the accuracy desired. The outfit itself is not too complicated and can be assembled a t a total cost of about $450. Operation is simple, and maintenance of the apparatus is negligible, although the circuit may require adjustment occasionally. The life of the counter tube is indefinite, but usually the good counting characteristics, if lost, can be restored by pumping and refilling the tube with counter gas. The advantages of the method are obviously such as to recommend it for general use.
50
40
w
230
-I L W
v)
I-
z
Q2C W I-
Acknowledgment
10
I2
II
DENSITY
1.6
1.8
FIGURE 4. EFFECT OF DENSITYOF SOLUTION ON COUNTING RATE 0 1 N KzFe(CN)n + 8ucroae 0 1 N KC1 4- ZnClz
To make a potassium determination by the radioactive method described here, the counter tube to be used must first be calibrated. This can be done with only two solutions of potassium, say 1 AT and 3 N potassium chloride. The observed counts per minute and the known densities of the calibrating solutions are substituted in Equation 4 and the constants k and a evaluated. The empirical relation between count, densitjy, and normality is thus obtained for the counter a t hand. For any unknown solutions, the counting rate and the density must be measured, the values substituted in the equation and the normality then calculated. The above method of correcting for the effect of density is applicable when the element in the salt mainly responsible for the high density is of atomic number below zinc (Zn = 30). The density correction necessary if elements of higher atomic number are present may be as much as 50 per cent greater and seems to depend on the element. For example, in trials with potassium nitrate solutions with barium chloride or with lead nitrate added to make the density 1.33, the observed count was 94 and 90 per cent, respectively, of the count obtained when zinc chloride was used to bring the density of the potassium nitrate solution to the same value. In general, compounds with elements of such high atomic number will not be found in amounts sufficient to contribute predominantly to the density of the solution, so that the correction determined as previously described may be used safely. However, if salts of heavy metals are present in high concentration, these had best be removed before the counting of the potassium solution is undertaken. As an alternative procedure, the counter tube may be calibrated with potassium solutions increased in density by addition of the salt present in the unknowns. On the basis of this work, an apparatus was installed for routine use in a control analytical laboratory and has been in operation for about 6 months. I n that time, many analyses have been made which could have been carried out by the usual procedures only with far greater expenditure of time and labor.
Conclusions The results presented in this report indicate that a rapid a n d comparatively simple determination of potassium can be
It is a great pleasure to acknowledge the help and advice of J. R. Dunning of Columbia University, J. W. Kennedy of the University of California, Berkeley, and R. C. Raymond of the Massachusetts Institute of Technology, in connection with the design of the counter circuit and of the tubes.
Literature Cited (1) Bramley and Brewer, Phys. Rev., 53,502 (1938). Brewer, Ibid., 48, 640 (1935). Ibid., 55, 669 (1939); J . Am. Chem. Soc., 59, 869 (1937). Brewer and Lasnitzki, Nature, 149, 357 (1942). Fenn, Bale, and Mullins, J. Gen. Physiol., 25, 345 (1942).
(2) (3) (4) (5) (6)
Heveay and Paneth, “Radioactivity”, 2nd ed., p. 236, London, Oxford University Press, 1938. (7) Langer, J. Phys. Chem., 45, 639 (1941). (8) ~, Latimer and Hildebrand. “Reference Book of Inorganic Chemistry”, revised ed., p. 449, New York, MacmillanCo., 1940. (9) Nier, Phvs. Rev., 48, 283 (1935). (10) Olson, Libby, Long, and Halford, J . Am. Chem. Soc., 58, 1313 (1936). (11) Rasetti, “Elements of Nuclear Physics”, p. 32, New York, Prentice Hall, 1936. (12) Smythe, Phys. Rev., 55, 316 (1939). (13) Smythe and Hemmendinger, Ibid., 51, 178 (1937). (14) Strong, “Procedures in Experimental Physics”, p. 298, New York, Prentice Hall, 1938.
Suspension of Glass Thermometers GEORGE BONA AND RICHARD ROWE Dictaphone Corporation, Bridgeport, Conn.
T
HE glass ring provided a t the top of glass thermometers for suspension from a hook, wire, or string often breaks off in handling because of its rigidity. If the thermometer itself is still in working order, it is usually suspended through a rubber stopper or cork held in place by means of a buret clamp. A better method is to fit a short piece of rubber tubing snugly over the upper end of the thermometer, so that about an inch of the tubing extends freely a t the top. A small hole is cut in the end of the tubing by bending 0.25 inch of the top down sharply and making a very short lengthwise cut a t the bend with a pair of scissors. The thermometer can then be suspended freely in the usual manner. As a matter of fact, new thermometers may be thus provided. I n this manner, the danger of contaminating a material with spilled mercury from a broken thermometer is considerably lessened.
