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INIIUSTRIAL '4XD ENGINEER1 VC C I I E l f I S T R Y
tlie control of temperature, for the controlled pressure is risrially suffirieirt to furiiish the motive power for its own control and it is merely necessary to arrange the mechanism t o follow a time schedule in a similar way to that in which ternper:iture operates. An interesting presstire-regiilatiii~device in wide use is thr ordinary rrduciiig valve. Here the admission of pressiire to t.he low-pressure side is cmtrolled by
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With these factors considered, it is possible to control accurately and automatically tlie temperatures needed in processes of exacting requirement8. and to do so with a eertainty of resiilts that will he duplicated from day to day. I'roducts will be uniform in composition and appearance and tlir waste resulting from uncontrolled runs will be eliminated. Moreover, the labor reqiiircd t.o m t c h over a large installation iri wliieli an operator is iiecded only for observing and regrrlatiiig will bn redured t,o a miniinurn. Acknowledgment
Tlir illustrations for this article hare becn kindly supplied by Taylor Instrument Co., Sarco CIL,Pulton Co., Foxboro Co., arid C. J. Taglinbric Co.
A Distilling Flask for Corrosive Liquids' By F. E. Brown
a mlve between the two. wliicli is in ttirii controlled hy tlit pressure on ilie low-pressure side. Proper Placing of Thermal Elements
Controllers, however cleverly made, carinot control ally temperature except that to which they are exposed. To state such a truism seems ridiculous, hiit the careless placing of ttiennal elements is responsihle for far more failures of automatic. control than the instruments thernselves. It must he borne in mind that temperatures through a mass may vary many degrees unless proper precautions are taken to secure uniformity; and also that in heating arid cooling it is almost impossible for a body to ctiarige its tenrperature uniformly. Such differences in temperature may be siifficient to make even the best control worse than useless. In installing the thermal elemeiit of such a controller several factors must he considered if proper results are to be secured: (a) The temperature throughout the mass must he as nearly uniform as possible and natural ciinveetion and conduction should be assisted by proper stirring devices. (b) The vessel containing a Ruid mass should be so designed and agitators so installed that no "pockets" of fluid will be left unexposed to the heatine elements.
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away from the mass"end is thus somewhat cooler or warmer. (d) It must be remembered that time is required for equilihriam to be reached no matter how efficient stirring may be.
has been using a modified flrisk, wtiidi is more difficult to refill, but which can be made in any laboratory arid lras no ground joints to crack or st,ick when subst,ances of high boiling point are dist.illed. To tlie top of an ordinary distilling flask is sealed a glass titlie. A , tlirough which tlie thermometer rvill pass. To its upper end is sealed a section of glass tubing, B, of larger diameter. The height of the flierrnorneter is adjusted by changing the length of a piece of glass tubing, C, which is so small t.hat the ring of the thermometer will not pass t.hrough it and so large that i t will not pass tlirough the small tube. The lower end of C should leave an opening so that liquid can drain from B back into the flask. After the flask is charged and tlie thermometer is adjusted, the upper end of B is sealed. The apparatus may be used indefiiiitely by cutting off the top of B a d sealing it again after recharging. * Received M a y 23. 1925. * Sattlri and Morfimer, THISJOURNAL. 11, 495 (192.3). Outlook for Alsatian Potash Production Brighter-According to Trade Commissioner Dank1 J . Reagan, Paris, the Alsatian pota3h mines have just obtained credits required for the construction of workmen's houses and for improving the production equipment. The present production sche&~lr,despite the low output in February, will permit French farmers t o obtain larger tonnages for the next scilson. and it is expectPd that the consumption this year within France will exceed that of last year. The recent delays in deliveries are gradually being overcome and the transportation situation has been eased somewhat. Of the 250,ooO tons of pure potash produced in 1924, 95,000 tons were u,sed in France. The present schedule calls for the production of 350.000 tons, of which it is estimated 150,OW tons
will be employed in France.
