ANALYTICAL CHEMISTRY
1848
systems as compared to the cell resistance for methanol alone. As many solvent systems may be provided for as are desired, by the addition of suitable resistors to the selector switch. Preliminary values can be obtained easily by measuring endpoint cell resistance through the electrodes with au ohmmeter. Values for R11 are equal to the differencebetween thecellresistance for the solvent used and that for methanol. I n preparing the various solvent systems for measuring comparative resistance, the end points may be established by measuring the largest break with a potentiometer or voltmeter as was done x-ith methanol in steps 3,4, and 5. In most cases, standard radio-type 0.6watt resistors singly or in combination can be employed t o obtain the required values in ohms.
The length of the capillary inlet tubing, after bending, was extended to about 20 mm. and the inlet orifice was not constricted, but left the full 0.5-mm. diameter of the bore of the capillary tubing. The outlet orifice w m constricted, but to only about half the diameter of the bore (Figure 1). This permitted m atomization rate of about 2.5 ml. per minute with an air pressure of 10 pounds per square inch-several times that of the regular Beckman atomioer, which has very constricted inlet and outlet orifices. In the Perkin-Elmer flame photometer this atomizer is held in place with a rubber stopper, and the liquid samples are supplied to it from a 5-ml. beaker that is held under it by a spring steel attachment fastened to the photometer hy the right front screws (Figure 2).
RepresentativeVaIues of R11 for a Particular Cell Assembly Oil,”%
Methanol Methanol-benrene
0
BSO
Methanol-toluene Metiianol-soctic acid
10.50
200
Electrodes used were No. 16 gage platinum wire sealed in glass Interelectrodo spacing was not found to be critical. LITERATURE CITED
(1) Kieselbach, R.,ANAL.Cw~nr..21,1578 (1949). (2) McXinney, C. D., Jr., and Hall, R. L.,IND.END. CHEM.. ANAL ED.,15,460 (1943). (3) Serfass, E. J.,Ihid., 12,536 (1940).
Modifled Beckman-Type Atomizer in the Perkin-Elmer Flame Photometer
Figure 2
Rolond T. Mueller Deportment of Subtropical Horfkulhre, Univerrity of California, Lor Angele., Calif.
N RECENT
years, flame photometry has become a n important
I technique in analytical chemistry, but the equipment has
not been perfected in every detail t o achieve the best results with the least inaccuracy snd inconvenience, particularly in regard to the atomizers. The Perkin-Elmer flame photometer has two types of atomizer: a metal atomizer containing a needle valve for regulating the rate of atomization, and B glass atomizer without a valve. Both have a “funnel” on top for introducing the sample and a tube on the bottom through which the compressed air enters. Neither atomiaer has been entirely satisfactory in this laboratory, because the glass one requires a large amount of sample to obtain an accurate reading; the metal one is subject t o frequent sir leakage and clogging; and with either one it is necessary t o wait until the SI\MPLE renainder of the sample in the Figure 1 funnel has been atomised before introducing a new sample, A Beckman-type atomizer, with slight modifications, was tried in the Perkin-Elmer flame photometer and found to be very convenient. This type of atomizer is similar t o that used with the early model of Beckman flame photometer. It was modified as folloms:
1
This type of arrangement has been in use in this laboratory for the past 3 years and has been found most satisfactory and timesaving far determination of sodium, potassium, and calcium in plant material, soil extracts, and water. No loss of instrument sensitivity or precision owurs with this modification, and there is no difference in instrument readings between the Perkin-Elmer atomizer and the modified Beckman atomizer. Small samples may be accurately read, very little clogging ocours, there is no air leakage of the atomizer so that a uniform rate of atomization is obtained, and it is possible to change samples immediately after a reading has been made, without waiting for the remainder of the sample to atomize. Readings can be made for about two samples per minute. This madifioation is less expensive and simpler than other modifications, such as that of Dubbs. [ANAL. CHEM:,24, 1654 (1952)l. Approximate dimensional mexrtsurements of modified atomizer (in millimeters) are:
O.D.
Bore Orifice at outlet O.D. at outlet Orifioe at inlet Len& of inlet extension alter bending
0
0.50 0.25 1.0 0.5
20
Air ohamber
O.D.
Length Orifice at outlet Air inlet tubing
12
30 2.0
0.n.
iength
40
