Temperature-Control D e v i c e for M a c M i c h a e l Viscometer W. A. RICE,
Tennersee Valley Authority, Wilson Dam, Ala.
TIIE .
conventional MacMichael viscometer is equipped with an adlustable heater which lacks positive thermostatic control. The equipment described here was devised to maintain the sample a t conRtmt temperature hy immersion of the sample cup in a bath through which water is circulated c o n t i n u o u s l y f r o m a thermostatically controlled rescrvoir. The bath assembly, which can be attached to theviscometer without permanent modif i c a t i o n t h e r e o f , is shown in Figures 1 and 2. It consists of nn o u t e r , a n n u l a r drain trough, a supporting jacket for the sample cup, and a water inlet tube.
Figure 1.
Disassembled Parts of Bath
The annular drain trough consists of t N 0 brazed c y l i n d e r s of sheet brass t o which a machined bottom and an outlet t u b e a r e soldered. T o attach the trough t o the viscometer, the sliding contact switch is removed from the ins . t r u m e n t and the tmugb is iastened in d a c e with the screws from t h e switch. Rubber washers are used toprevent leakage around the screws. The supporting jacket for the sample
cup, together with its integral ehmnel for intake of water, is turned from solid brass stock. The body of the jacket has the same outside dimensions as the outer cup supplied with the instrument. The baffles, drive studs, and outlet tube are soldered in place. A bead of solder on the outer rim facilitates measurement of the rate of rotation. Water a t constant temperature is introduced into the intake channel of the jacket through a small gooseneck. The gooseneck is clipped t o the outer edge of the drain trough, as shown in Figure 2, and is inclined about 60' in the direction of rotation of the jacket t o minimize the development of a rtmding wave in the intake channel. The path of the water through the bath assembly is shown by the arrows in Figure 2. Water from the intake charnel flows through gate A into the space between the sample cup and its supporting jacket, where it is deflected downward and across the bottom of the sample cup by the two vertical fins, F, on the inside of the jacket. The overflow empties through gate B, which is isolated from the intake channel by dams D, and spills into the drain trough. With adequate thermosintic control of the souw of thc water niid with a circulation r a w wf about I liter prr niinutr through tho t ~ s t l irunrrolof , t1.e ternperntureof thcrnmplc t o within * O . I o C. is attained ensily und+r thP atniosplteric contlitiona prevailing in th? u w 8 1 ldxxntory. The iollwving dimensions XP rc
