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ASALYTICBL EDITIOS
ascarite bulb showed a change in weight. On this basis i t was assumed that the change in weight of the first ascarite bulb represented the weight of the carbon dioxide contained in the k n o m volume of the mixture. T h e volunie used for these determinations was 2100 ml. Three of the air-carbon dioxide n-ere then made in the apparatus herein described. -4tabulation of the results, expressed as parts of carbon dioxide by volume in 10,000 volumes of the mixture a t 28" C. and 760 niin., is given belom-.
RLN 1 9
Vol. 2, s o . 2 k f O U I r l c D PETZRSOY-
STA~DA METHOU RD 115 3
PALMQLIST METHOD 118 2
115 8
3 Average
117 6 119 4 118 4
115 5
If care is exercised in the selection of a uriifuiin capillaiy for tube I , the accuracy of the method may be correspondingly increased. Literature Cited 11' Xnder~on,J
I m Chem Soc
,
35, 96 (1916'.
Some Improvements in Thermoregulators' Henry J. Wing
I
S A former paper ( 4 ) a nev- type of thermoregulator n-as
described. One of its features was the fact that toluene could be used without danger of fouling the mercury surface. I n the further development of the regulator mentioned above a reservoir shaped as shown in Figure 1 has proved very effective. A thermostat made from an uninsulated 20-liter stoneware crock has been maintained for several hours a t 37" C. with a variation, as measured bv a Beckmaim therm o i e t e r , of *0.002" C. Of course, the type of h e a t e r , t h e relay, the suspension of the regulator, the stirring, and insulation of the bath all h e l p t o determine the regulation of any thermostat (1, 2 ) . I n order to maintain this degree of control, the regulator is suspended so that i t is continuously shaken by t h e v i b r a t i o n of t h e stirrer. An ordinary 20ohm relay may be used with this regulator. However, the f r e q u e n t opening and closing of the circuit soon wear out the contact points unless a very small heating current is used. The current-carrying capacity of the relay niay be greatly increased if the ordinary c o n t a c t points are removed and flat plates of pure silver, 10 mm. in diameter and 3 nim. thick Figure 1-Thermoregulator and fastened bv means of countersunk screws, are substituted. If a 0.5-microfarad condenser is used in parallel v i t h these contact points, currents u p to 2 amperes a t 110 volts'can be easily handled. The new regulator is made entirely of Pyrex. The regulator head, the other new feature, may be sealed to any form of bulb. The contact leads a t 9and B are of tungsten, which can be sealed through the Pyrex. The bulb is filled with 1 Received January 20, 1930. Publication approved by the Director of the Bureau of Standards of the U. S. Department of Commerce.
iiiercuiy and toluene and the nliole heated t ( J iliiie uff dissolved air as described in the previous paper, or tlie toluene may be heated almost to boiling to expel the air aiid n i q tlirii before i t cools be filled in, through H , on top of tlir iiiei cury. H is then sealed off. The contact chamber is filled n i t h hydroqeii Tliib ii accomplished by filling the whole regulator n ith niei ~ uy,i tlie tube C being unsealed. A stopcock is then attaclird to C by means of rubber tubing. Hydrogen from a cyliiitlcr 15 allowed to enter, making sure that all connecting tubeb ale washed free from air, until the mercurv is forced some diitance below the contact point, D. The stopcorks a t C and E are both closed and the hydrogen tube is removed. The K stopcock a t C is opened and C is immediately sealed off as shown. T h e expansion and escape of some of the hydrogen during the sealing process cause the mercury to be forced u p above the contact point, D. If the height of the mercury above t h e c o n t a c t D is not too g r e a t , t h e setting of the regulator is accomplished by suction through a tube fitted to the cup a t E by means of a rubber stopper. The use of Pyrex makes this new modification much easier to build than the old. In addition, this new design lessens the danger of breakage when making electrical connections. T h e s e c o n nections are made through mercury in the cups F a n d G. It has been pointed out ( I ) that iron i s a b e t t e r m a t e r i a l for the contact point than platinum because mercury does not wet iron. It has been found that tungFigure 2-Thermoregulator of sten has this same advanSensitivity t o 0.5" C. tage. C l e a n m e r c u r y i n c o k a c t with the tungstkn wire shows a depression around tlie wire, indicating no tendency to u-et it. The usual formation of oxide a t the mercury contact surface _I_
permits the use of only very small relay currents with most other regulators. Since the contact is always made in an atmosphere of hydrogen, the amount of current which may be used in this regulator is limited only by the volatilization of the mercuiy a t the contact point. If too large currents are used, the mercury will spatter an-ay and so cause the bath temperature to vary. Currents u p to 0.5 ampere may be used if a small coiideiiser is placed in parallel with the contact. Hoir ever, better regulation is obtained with small currents. I n operation this regulator is entirely closed. Hence there is no danger of mercury vapors no matter what the temperature of the heated bulb may be, provided the pressure does not becomr too great for the instrument. Therefore this type of regulator has been used to control furnaces a t temperatures even above the boiling point of i-nercury (3). This is accomplished by making the vertical distance from the heated bulb to the stopcock E about 30 cin. or more. The pressure of this coIuniii of mercury prevents the boiling of the mercury a t temperatures well above its normal boiling point. If the heated bulb is horizontal, the mercury in the tube below E is not heated by convection. This is important in order that the grease in the stopcock may not be melted. Better regulation is obtained if capillary tubing is used. The useful range of the mercury thermoregulator is thus extended from the freezing point to above the boiling point of mercury. Lowtemperature furnaces may be easily regulated without resort to expensive equipment. Less-Sensitive Thermoregulator I n many cases i t is not necessary to control a constanttemperature bath to 0.001" or 0.01' C. There are bimetallic
regulators on the market, for use in a thermostat, which will respond to a change of approximately 1.0" C. The regulator shown in Figure 2 is intermediate in sensitivity between the very sensitive mercury regulator and relay and the bimetallic regulator. I t operates differently from the other in that the expansion of the regulator liquid directly opens the heating circuit. It will make and break a current of 0.5 ampere a t 110 volts without trouble. It has been used with currents a i high as 1.5 ampere a t 110 volts. If more than 55 watts energy is required to heat the bath, it is supplied by other heaters so designed that they mill not keep the bath a t quite the desired temperature. The final heating is accomplished by a 50-watt heater in series with this regulator. I t s sensitivity is *0.5' C. over a period of several hours. Changes in barometric pressure will have some effect on the temperature of the thermostat. The entire regulator is made of Pyrex and the electrical lead wires are of tungsten. Varying amounts of hydrogen were tried in the contact chamber. A comparatively small amount, as indicated in the illustration, was most effective. This regulator is filled with hydrogen in the same way as the one first described, but in the sealing-off process the tube I
