Low-Lag Toluenz Thermoregulator PAUL E. SNYDER
AND
HARRY SELTZ
Department of Chemistry, Carnegir institute of Technology, Pittsburgh, Pa.
HE conventional glass mercury-toluene thermoregulator suffers because of the poor heat conductivity of the elsss, which gives rise to an appreciable thermal lag. For use in highprecision, isothermal bomb calorimetry, a constancy within *0.001" C. is desirable, and for this purpose a specially designed regulator using a thin copper container for the toluene was constructed and found satisfactory. The most important feature of this regulator is the means of obtaining a successful glass-tometal seal (Figure 1). To one end of a 3.0-cm. length of 2-mm. Pyrex capillary tubing is sealed a 5.0-cm. length of glass tubing 10.0 mm. in diameter. This is the end in which the adjustable contact is eventually laced. To the other end of the capillary is sealed a 30.0-cm. Ength of 60-mm. diameter tubing. Just below the end of the capillary, about 3.0 cm. of the 6.0-mm. tube are given a heavy coat of platinum deposited from the usual platinic chloride41 of lavender solution by heating with a blast lamp. The platinum is then given a very heavy dense electroplatin of copper from a sulfate bath. This complhted glass part is S o w n a t a, Figure 1. b and c were turned from hard-drawn copper bar stock. The walls of these pieces are made as thin as possible to obtain some degree of flexibility. The bore of b is made to fit snugly on the copper-plated section of the glass tube. Then b and c are brazed together to form part d . The double cu resulting ie sli ped over the copper-plated part of the lass d e , e, and the tu!e is connected to a steam source. After t i e whole has reached steam temperature, Wood's metal is allowed to flow into the joint, using dilute hydrochloric acid as a flux. After cooling, a perfectly tight s e d between copper and glass results.
Figure 2. Head and Body of Regulator
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b
b
The sssembled body is now laced in the recem in the lower side of the head and soldered tigEt. This gives the nearly completed re lator showri in e. eh% ! final step is to install the glass tube. The head is heated gently until Wood's metal can be melted In the groove, which is then filled almost to the top. Dilute hydrochloric acid is again used as a flux. The glass tube is inserted in the hole in the head as far as it will go. This causes the inverted part of the double cup to seat in the groove. Immediately the head is cooled with a damp cloth, so that the molten Wood's metal solidifies before that between the cup and the glass melts. The assembly is now complete. In order to fill the re ulator, a measured amount of mercury is placed in the glass cup %y way of the glass tube. This amount is such that the lower mercury level will be about in the middle of the cu a t operating temperature. Purified toluene is then run throug! the threaded hole a t f. When full, a screw is tightened in the hole, using a lead washer to obtain a mechanical seal. Then the screw and washer are soldered to the head with Wood's metal.
C
e
a Figure 1.
This regulator in conjunction with a suitable electronic relay circuit will hold the temperature of a bath to within 0.001 O C. for hours a t a time. One contact of the regulator is grounded to the bath fluid. This drawback can be taken care of by using an isolation transformer in the relay circuit.
Debilr of Glass-to-Metal S a l
The next step consista in makin the head and body of the regulator (Figure 2). a is turned from brass and is 5.0 cm. in diameter and 2.2 cm. thick. The hole is such a size (1.5 cm. in diameter) that the bottom of d, Fi re 1, is a snug fit in it. The outer cup of d, Figure 1, fits groove in the to is made so that in it loosely. {or this, the groove is 22.0 mm. in diameter and 5.0 mm. deep. b is made of 2.5-cm. inside diameter hard-drawn copper tubing 26.0 cm. long with a bottom brazed on. c is a lsss cup, abaut 5.0 cm. long and 2.5 om. in diameter, fitting insije b, and cemented in with p roxylin cement. The copper wire, d , is brazed to the inside of t i e copper tube and to the lower end of i t is welded a length of platinum wire which reaches into the cup where, in the final assembly, i t makes contact with the mercury.
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Geiger-Counter X-Ray Spectrometer The f i s t Geiger-counter focusing spectrometer to be developed hrr been announced by the North American Philips Co.. Inc., 100 Emt 42nd St., New York, N . Y. It provides a new method of m a b g quantitative and qualitative analyses of crystalline and certain amorphoue substances in the paint, chemical, ceramic. rubber, and metallurgical fields; under optimum conditione of resolution accuracy of i0.03' ia obtainable.
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