Device for Opening Small Sealed Objects under Vacuum G. P. Schacher, General Engineering Laboratory, General Electric Co., Schenectady,
in mass spectrometry analysis, samples of gas from hermetically sealed containers must be analyzed. often to identify the presence of the components of air. The elimination of atmospheric contamination in such studies presents a major problem. A versatile, easily constructed, sampling fixture has proved very useful in handling such problems. FREQUENTLY
At one end of the device a 12/30 standard-taper joint and stopcock are attached, so that the sampling system can be directly incorporated into the mass spectrometer system. At the other end of the Pyrex KO. 7740 tube a stainless steel flange is attached to the Pyrex No. 7740 through a glass to Fernico seal. A matching steel flange base and neoprene O-ring completes the collecting bottle assembly. The base section has two stainless steel support rods to hold the adapter for the specimen to be examined. T o open a sealed container with this fixture, the object is inserted into a suitable adapter, and the steel point, operating through a stainless steel bellows, is advanced just far enough to hold the object in place. The flanges are then tightened, and the system is
evacuated on the mass spectrometer sample system. After evacuation, the object is punctured by turning the knurled knob to apply pressure through the threaded rod to the steel point.
5 JOINT 4 MY. STOPCOCK
BREAKING POINT
ERNICO TO GLASS 0 RlNQ SEAL
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N. Y. The gas released into the sampling vessel can then be introduced into the mass spectrometer without atmospheric contamination. Condensed moisture and adsorbed gases are often problems, because of the use that has been made of some specimens. The adsorbed surface gases can be removed by winding a resistance heating element about the base section of the tube, and heating during the evacuation stage. I n this manner, a n encapsulated gas specimen can be examined without contamination by surface adsorbed gases. This fixture has made possible the analysis of gases in such devices as vacuum tubes and small sealed relays. The most recent application has been the determination of the nature of the gas contained in microbubbles in glass. I n this case, the glass specimen was held in position by the steel point. The point was positioned so that, on tightening, it punctured the glass, and released the entrapped gas from a bubble directly below it. Using this device with a General Electric analytical mass spectrometer, the gaseous composition of samples of less than 1-cu.-mm. volume a t pressures of less than 0.5 atm. has been determined,
Automatic Potentiometric Titration in Determination of Dissolved Oxygen V. S. Griffiths and M. I. Jackman, Chemistry Department, Battersea College of Technology, London, England
of dissolved D oxygendetermination by a method involving a URING
redox titration, an automatic apparatus was developed. The titration was followed potentiometrically by using an electrode pair, comprising a glass reference electrode ( I , 3-6) and a platinum indicator electrode. A glass electrode was used as a reference, as it introduces no extraneous ions into the solution nor requires replenishing. By a suitable choice of electrode contents ( I ) a shift of end point potential may be obtained, thus making the method more convenient electronically for use in an automatic apparatus.
trapped. One milliliter of manganous sulfate reagent was added and mixed, and 1 ml. of potassium hydroxide solution. The whole was well shaken, allowed to stand for 2 minutes, and then 8
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shaken again prior to the addition of 1 ml. of sulfuric acid. Addition of larger amounts of sulfuric acid did not affect the end point. A suitable aliquot of the mixture was taken, 1 ml. of phos-
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Automatic titration for dissolved oxygen determination
EXPERIMENTAL
Thc reagents were 48% w./v. nianganous sulfate, 70% wv./v.potassium hydroxide, concentrated sulfuric and phosphoric acids, and 0.0125N ferrous ammonium sulfate in 4% n../v. sulfuric acid. Glass-stoppered reagent bottles containing about 120 ml. were filled, care being taken that no air bubble was
D.O. IRON METHOD,P.P.M. VOL. 31, NO. 1, JANUARY 1959
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phoric acid added, and the solution titrated with ferrous solution, using the automatic titration apparatus. APPARATUS
The electrode system, a lithium glass electrode and a platinum wire spiral, was connected to a millivoltmeter and recorder, while titrant was added by means of a variable-speed titration unit connected to a volume counter and recorder and their associated power supply. The titration unit could be switched off automatically a t the end point by a phototransistor control ( 2 ) on the millivolt recorder. The titration unit comprises a variable-speed motor driving a n Agla micrometer s-yringe (Burroughs, Wellcome 8: Co., Inc., Tuckahoe, N. Y.) through suitable reduction gearing to give final delivery rates of 0.01 to 0.3 ml. per minute, although this could be extended by using larger syringes fitted
to the same micrometer head by a n adapter. The volume of titrant delivered was metered by causing the micrometer head to actuate a n electromagnetic counter with delivery of each 0.01 ml. When the potential of the electrode system is being recorded, an electromagnetic pen is connected in parallel with the volume counter, so that volume of titrant and system potential are simultaneously recorded.
The average deviation from the mean on samples titrated was 1.85% using the ferrous method and 3.94% using the Winkler method. The average value of the end point potential using the glass-platinum electrode system was 524 mv., while the average rate of change of potential at the end point was 4500 mv. per ml. of 0.0125N titrant.
RESULTS
(1) Griffiths,V. S., Stock, D. I., J . Chern. SOC.1956, 1633. (2) Jackman, M. I., Lab. Practice 7, 526 (1958). (3) Lykken, L., Tuemmler, F. D., ANAL. CHEY. 14, 67 (1942). (4) Ohlweiler, 0. A,, Meditsch, J. de O., Eng. e quim. 5 , 10 (1953). (5) d’ombrain, G. L., Griffiths, V. S.,
LITERATURE CITED
Simultaneous determinations of dissolved oxygen were made on water samples by the ferrous ammonium sulfate method and the conventional Winkler (6) method. The range studied was from 0.1 to 8 p.p.m. The results obtained by each method and their spread are shown on the graph, together with the line of theoretical slope.
Stock, D. I., Proc. Conf. Soc. Inst. Technol., Swansea, England, September
1957. ( 6 ) Rinkler, L. W,, Ber. 21, 2843 (1888).
A Modification of the Fisher-Serfass Electronic Relay A. C. Andrews, E. B. Beetch,’ and C.
H. Whitnah,
Chemistry Department, Kansas State College, Manhattan, Kan.
of the Fisher-Serfass elec0 tronic relay a t current levels near the maximum causes arcing with subsePERATION
quent burning of the contact points, especially where refrigeration compressors are used in conjunction with a mercury contact regulator for temperature control in constant temperature water baths. A description of a modified Fisher-Serfass electronic relay to eliminate the above difficulties is reported here. This device has been used with very satisfactory results. Essential features of the wiring diagram are shown in Figure l. The portion of the circuit involved in the modification is outlined by the dashed lines. The relay, A , was changed by removing the upper contact point. The contact point on arm E of relay A was wired t o one side of a 60-volt direct current source, while the lower contact point F was connected to one terminal of the actuated electromagnet of a single-pole, double-throw rocking mercury switch H. The remaining terminal on the electromagnet was connected to the other side of the 60-volt direct current source, thus completing the circuit as shown in Figure 1. A mercury switch operating on exactly 60-volt direct current is not essential, as switches with voltage ratings of 40- to 60-volt direct current were satisfactory. The 60-volt type was incorporated here, because of 1 Present address, Research Department, Rahr Malting Co., Manitowoc, Wis.
162
ANALYTICAL CHEMISTRY
il00
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5.1ME
0.51 MEG.
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Figure 1. Schematic wiring liagram showing details of alterations on FisherSerfass electronic relay -
its availability. The function of the pilot light, D, in the circuit iTas‘not changed. Incorporation of the single-pole, double-throw rocking mercury switch made available a normally energized 110-volt outlet or a normally deenergized 110volt outlet depending upon the desired application. Terminals of the mercury switch were connected to 110 volts as shown in Figure 1; two terminals were connected to a common lead and the other two terminals were connected through outlets Cl and CZ. The mercury contact regulator, or other controlling element, is attached to the jacks, 0. I n the arrangement as outlined, relay A merely actuates the
mercury which closes the 110-volt alternating current circuit. Thus, the 110volt circuit is isolated from the contact points of the relay, a n important factor when high operating currents are encountered. Many of the electronic relays designed for automatic control are similar, therefore the suggested modifications presented here might be applied t o other circuits. An immediate practical application of this type of apparatus is in modifying circuits similar in type to those of the Fisher-Serfass electronic relay. TAKENfrom the Ph.D. dissertation of E. B. Beetch, Kansas State College, Manhattan, Kan., 1957.
