H T 1R.X H. I)EKH\’
It has frequently been found necessary in this laboratory to obtain a constant temperature by means of a circulating liqtiid. n‘orking with different methods! we found that any circulatory apparatus should be considered in respect to the following points : Rapidity of circulation ; ( I ’) ( 2 ) Ease of coiistriiction ; ( 3 ) Econoiii!. oi operation ; ( 3 Rapidity of adjusting and InaintaiIiiiig the teinperature ; ( 5 ) Vsefulness 3ver a great range of temperature. One method which has hitherto beeii employed was that of Cad!, the apparatus for nliicli in constructioii aiid operation is apparetitl!. the ideal of siniplicity. I t was found, however, that the apparatus was sonieivliat difficiilt to regulate in consequence of the liquid haying the tendency to siphon out when tlie speed of tlie motor n a s not well regulated. Xnotlier objection \vas that it was necessar!. to maintain the level of the liquid in the 1ia.th constant. .Inother apparatus which we have employed, consists of a force pump, driven b?- an electric motor. Although this form of apparatus produces an excellent circulation and steady uniform flow of liquid tlirough tlie constant teiiiperature chamber, the initial expense and the power required to operate it preclude its use except in a f e n isolated cases. hloreoyer the expansion of the metal when heated to a higher teiiiperature. makes it ixnpossihle t o obtaiii a stuffing-box which is tight. One has, tliere-
fore, to resort to glass apparatus, a i d adopt principles quite different from those employed in the force-pump. 'I'he first form which has been used for tlie circulation of liquids froiii a thermostat to tlie apparatus whose temperature is to be kept constant is shown i n Fig. I. In this diagram €3 rep-
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f i ( v Dcz,icc.s for
Circulating L i p i d s
I9
forms a closed s>.iteni, the rotation of the propeller must continuall!. force liquid into arid through the jacket a t a rate which is a function of the speed of rotation and the size and length of the tubes C and D. Ry use of this apparatus, which is extremely easy to make and to manipulate, very efficient circulation is obtained. It is absolutely necessary, however, to provide a stirrer for the bath R. To obviate the iise of the circulating and stirring apparatus iii separate parts, the second method was devised. T h i s is illiistrated by Fig. 2. As in the previous case, B is
4
Fig.
2
tlie bath, A is the jacket, C and D are the outlet and inlet tubes, both of which pass below the mrface of the liquid i n the bath, T h e tube C is encircled by a loosely-fitting glass tube E, the lower end of which is blown to a bulb of diameter about 7 cm. In this bulb are blown two holes, H, of the diameter of I cm. T o the shaft E is attached a driving wheel G, which is connected
to an electric motor by means of a belt. R!. means of suctioii applied at F, as in the preceding case, A , C, and D are filled with liquid. By now rotating G E rapidly, the liquid is by centrifugal action thrown away from CC, passes out throngh the holes H and causes the liquid to flow in the direction DACC (siphon action). T h i s form of piinip also acts as a very efficient stirrer, since the liqiiid thrown out of the holes in the bulb is scattered in the form of a fine spra!. tliroiigh the liquid in the bath. T h i s was proved in preliniinar!. experiments by rotating a stirrer of this general form, but provided with a sniall hold i n the bottom, in a tlvo liquid la\-er system of sulfuric acid and toluene, when the acid was thron-n in a verj. fine spray through the toluene. ;Idditional proof was shown in a very pretty inanner by the use of a colorecl solution in the tube CC. By means of this apparatus, it was found possible to keep the temperatiire of the jacket A constant within a fraction of a degree at 90'. There is always a slight difference between the temperature of the bath and that of the jacket, depending on the amount of surface exposed to the air. Riit t h i q is so constant that it causes little or no trouble. T h i s apparatus obviates the objections which we 1iai.e found in Cady's ; if the connection at F is tight, there is no tendencj, for the liquid to siphon out of the jacket, nor is it neceisary to keep the level of the bath constant. T h e method has been subjected to a number of tests in circnlating liquid in baths for vapor-density, gas voltinie, and other work, and so far as the five points mentioned above are concerned, it has been found ver) sat isf act ory . CO?~?~fll CillvrYszfy, ]IC
ire.
I 900
