Radiant Heat Still for Pure Water Kenneth Hickman, Rochester Institute of Technology, Rochester 8,
T"researchthe requirements of another 3) a still was assembled
of, or more than the listed concepts; only the basic air cooled version is described.
MEET
(2,
for producing without iuterruption for months at a time a small flow of water having a specific resistance of about 2 megohms per em., em.% Since the requirements have heen met and the still is simple, it is here described together with the conccpts underlying the desicn, which were: That a transparent boiler heated by infrared lamp will permit heating throughout the body of liquid without the walls becoming hot enough to acquire scale. That the crude water shall be considered to contain many trace volatile substances (1) and will then require multi-effect fractional distillation including reboiling and rejection of light ends. That with countercurrent degassing much of the temporary hardness can be deposited before the water enters the still. That with a combinstion of infrared heat. suitablv induced ebullition. and surface overflLwing, permanent hardness can he rejected from the still without scale heing deposited inside. That optionally and without serious loss of efficiency, the unabsorbed visible radiation can he used for room lighting.
N. Y.
Air-Cooled
'
Radiant-Heated
Still.
Figure 1 shows a 2-liter round-bottom borosilicate glass flask, A , with wide elongated neck which rests in an insulated reflecting tube, B , and is supported in slots by two glass knobs, C, and the overflow tuhe, D. A condenser tube of 2-cm. diameter, 140 em. long, and slanted t o reject air is sealed t o the nrck 5 cm. above the flask, while a rehoiler, E , is attached a t the start of the condenser. A short water cooling jacket prefrrahly demountable for cleaning, is fitted to the upper leg of the condensrr, its sole purpose being to grewarm the feed water. Situated within the neck of the flask is a funnel terminating in a tube of correct diameter (6 to 8 mm.) to supply purge-steam to the incoming feed. A flattened bulb with a small hole serves as a guard for the steam scrubber (conveniently furnished by a copper dishscouring pad from the hardware store) which is fastened around the tuhe. A similar scrubber serves as a oackine for the funnel. The reboiler. which lies nearlv horizontal, can be warmed by a heatin; taoe laid alone the underside and secured in place by thermal lagging. The apparatus is completed with a 375-watt I
industrial type radiant heat lamp, a crude-water filter, G, metering valve, H , shut-off valve, Iineuse where there is a convenience break (a gap of a few millimet,ers) between still and the author's research apparatus (2, 3) the conductivity increases 20 to 30y0 a few minutes after an operator enters the room in the morning, and rises progressively during the day but recovers overnight. Variations of the described apparatus will occur to the reader, although oneimmersion of the heat lamp for greater thermal efficiency-has not warranted the complication involved. Other modifications which add regenerative features are being studied. Care and Maintenance. With the Lake Ontario water supply the sponge in the feed tube required renewing after nine months' continuous use and the tube was cleaned with acid. The overflow trap, a 50-ml. test tube, required a year to accumulate the sludge shown in Figure 2, left. The glass boiler became heavily etched by the hot water but t,his has not yet noticeably affected the efficiency.
Table I. Performance of Lamp-Heated Water Still
Spectitic resistanre
Steanr issues from distillate," -Feed megohms entrance denser of
-
0 5 0 6 1 1 1 7
2 4
1 7 3 Ih
Yo Yes
~
Xo Yo
Yes Yes
Yes Yes
Yes Yes
Yes
Yes
Yes Yes
Power input to reboiler, watts 00 00 00 5 0 10 0 17 0 LO 0
a Feed water is Ontario Lake water, Rochester, N . Y. City supply total solids average 170 p.p,m. Ratio distillate to feed water fluctuating around 1:4 volumes. After extended operation.
LITERATURE CITED
(1) :$rmstrong, F. A. J., Boalch, G T., ,\ature 185, 76:! (1960). (2) Hjckman, Kenneth, .\'alure 201, 985 (1964). (3) Hickman, Kenneth, Ofice qf Saline Water Annual Rppt. 1062, pp. 4-6.
Improved Precision of Calorimetric Measurements by Differential Thermal Analysis Edward M. Barrall' and L. B. Rogers,z Department of Chemistry, Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, Mass.
PR0CI:I)URE for difthermal analysis (DTA), the sample is run against an inert reference material-e.g., calcined alumina or carborundum-to make certain that any phase changes can be assigned unambiguously t o the sample. Once the apparatus has been calibrated, either the peak height or the area can be related t o the heat clf transformation for a ]lure sample or to the amount of an active constituent ,)resent in a misture. Ordinarily, the uncertainty in the final result is about 5%. Classical calorimetry is much more Irecise, but it is also comparativdy time-consuming. The purpose of the Iresent study was to determine whether the iirecision of differential thermal anal increased to a competitive level by measuring the diffewnce b e t w e n a U
TITI.: USUAL
I-ferential
Present address, C:ilifornia 1iese:irc.h Corp., 576 Standard Ave., I?ic*hniond, Calif. * Present address, 1)epartment of Chemist,ry, Purdue University, Lafayette, Ind.
sample and an active reference substance used as a standard. The approach was tested by determining the difference between the heats of transition of two low-temperature forms of silver iodide, each of which goes t o the same high-temperature form a t about 140" C. Stephenson and Waldbaum ( 3 ) have not only confirmed by x-ray esamination the esistence a t room temperature of pure hesagonal and ]lure low-temperature cubic forms, but they havr also reported reliable preparative methods for each. Using conventional calorimetry they determined the heats of solution in aqueous potassium iodide to be -2080 1 5 0 calories per mole for the hesagonal form and -2360 r60 ralories for the low-temperature cubic form. EXPERIMENTAL
Chemicals. Sincr t h r prc,parative p r o ( ~ d u r r h for the pure c q ~t:ilhnr modification\ of t h r low-tompcmturr formi of iilvrr iorlid(x h a w , to tlatr, been publi.hed only in Kaldhaum'h
t,hesis (S),they will be outlined here. After a 3.11 aqueous solution of 110tassium iodide had bcen saturated with silver iodide, the pure hexagonal form of silver iodide was precipitated by adding distilled water. l3ecause the silver iodide was to be diluted with carborundum for the differential thermal measurements ( I ) , the precipitation was carried out in the presence of 10 grams of 500-mesh varborundum. Thus, the need for grinding the two solids together to produce a homogeneous mixture was avoided, and the possibility of converting some of the silver iodide to another crystal form was minimized. The carborundum-silver iodide mixture was filtered, lvashed with water, and dried in a vacuum debiceator for two days. 'The mixture cwntained 20.070 silver iodide as dcterminrd t)y weight loss upon rxtraction of two 3-gram samliles Lvith saturated aqurous potassium iodide. 'To malic lo\\.-trrnI)(,raturr c.ubic>silver iodide ( 2 ) , silver iotiitlc \\-as dissolved in a solution of >ilvw fluor>ilic.ate made hy hatrirating hyeir.ofliiodic acid with silver oxide and filtwing t o i'cniove oxide and ioclitlr. .\fter 10 grams of 500-rnc~sh cwt)oi~undumhad h e n aticled to thc wlution. silver iodide VOL. 36, NO. 7, JUNE 1964
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