ANALYTICAL EDITION
July, 1945
are kept in the dark at 7 " C. The atandard deviations and coefficients of variation for all samples are shown a t the bottom of Table 11. The apparatus for separating the carotenoid pigments has several advantages over that used previously. The outlet tip of the adsorption column is high enough so that it will not go dry unle.;s pressure is tzpplied. Solvents can be added to the column as required while continuous pressure is maintained. This increase? the speed of the determination and decreaseq the tendency for pockets to develop in the adsorbent. SUMMARY
Uding apparatus described i t was pos$ible to determine total chlorophyll, percentage chlorophyll a , @-carotene, and to estimate xanthophyll concentration within an hour from the time a leaf sample was removed from the plant. The standard deviation of the total chlorophyll and carotene results obtained by
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this method was less than 2% of t,he means and thht of the percentage chlorophyll a less than 0.3% of its mean. Total xanthophyll determinations were less accurate than those previously reported. The apparatus eliminates possible loss from the many transfers in the older procedure, decreases t,he amount of apparatus required, increases the speed of dfattmninations, is easily constructed, and is self-cleaning. LITERATURE CITED
(1) Coniar, C. L., IXD. ENG.CHEM., ANAL.ED., 14, 877-9 (1942). (2) Coniar, C. L.. and Zscheile, F. P., Plant Physiol., 17, 198-209 (1942). (3) Griffith, R. B., and Jeffrey, R. N., IND.ENG.CHEY.,- h . 4 1 , . ED., 16, 438-40 (1944). (4) Schertz. F. >I Plant ., Physiol., 3, 211-16 (1938). THEinvestigatioii reported in this paper is in connection with a project of the Kentucky Agricultural Experiment Station and is puhlishecl hy perniiasion of the director..
Thermostatic Bath for Low Temperatures E. L. RUH, G . E. CONKLIN, AND J. E. CURRAN Oil Development Co., Bayonne, N. 1.
Standard Inspection Laboratory, Standard
A thermostatic bath, primarily for low-temperature viscosity determinations, operates effectively at temperatures ranging from +40° to -70" F. It consists of a three-stage installation, one bath containing dry ice and isopropyl alcohol, a second bath maintained under rough automatic control, and a third bath under close control. The last is a vacuum-jacketed glass jar, filled with acetone, and equipped with sccessories for mounting viscometers. The development described superseded one involving only two stages. This was effective, but the first stage required time-consuming manual control of temperrture. The three-rbge installation is mounted in a special cabinet which augments its operating efficiency.
THE
laboratory with n-hich the authors are associated ninkcs niiiwrous viscosity determinations at temperatures ranging fro111 +10" to -70" F. The bath originally used contained wetone which was kept chilled by periodic immersion of a cylindrical, perforated basket filled with dry ice. Reasonably good temperature control was obtained by this method, but it was t iine-consuming. Development and construction of a bath with automatic temperature control were therefore undertaken. PRELIMINARY EXPERIMENTATION
q u a n t i h of dry icc from time to time. This necessitated experience on the part of the operator, and a considerable waste of his time. G E N E R A L FEATURES OF F I N A L D E S I G N
Experience with the two-bath unit pointed to the desirability of a three-bath system, which is now in service. It consists of one jar held a t a suitable low temperature, containing solid carbon dioxide and isopropyl alcohol: a second jar under rough thermostatic control; and a third, Dewar-type jar under close control. The temperature-control system of the second jar is identical with that used in the earlier two-bath unit. The third bath is chilled continuously by circulating its acetone through the coil in the aecond bath which is held a t a temperature approximately 10" F. lonw than that desired in the third bath. Temperature control in the latter is effected by a conventional circuit consisting of a 125-watt knife-blade hcater, a bimetallic thermoregulator, and a suitable relay. The three-bath design provides the d e h e d close temperature control (within *0.1" F.) in the Dewar jar with a minimum of attention from the operator. After the initial adjustments have been made, all that is necessary is to add to the first bath enough dry ice to keep its temperature a t least 30" F. below the temperature required in the Dewar jar. This requires much less attention than holding the temperature of the same bath between maximum and minimum limits.
Trials were made of an apparatus consisting of a large Dewartype jar filled wit,h acetone, chilled by circulation through a copper coil immersed in an insulated glass jar containing isopropyl alcohol and dry ice. Motor Motor The pump was operated continuously to stir the acetone bath. The coil in the cooling- bath Maanetic was by-passed part of the time by a magnetically operated three-way valve connected with a suitable relay, actuated by a bimetallic regulator in the acetone bath. The regulator also turned on an immersion heater, whenever the flow through the cooling coil W M interrupted. This was found t o help in maintaining close control. This installation gave satisfactory results when the temperature of the cooling bath bore the correct relation to the temperature desired in the -. acetone bath. BathNo.3 Both No.1 Bath No.2 I t was necesbary, . . hoivcver. to give the coolDiagram of Three-Bath Thermostatic Installation for Low Temperatures ins bath much attention, putting in the proper Figure 1 ,
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 17, No. 7
The bimetallic type of regulator was selected because of the ease with which i t could be set for any temperature a t which the bath is required to operate. The ones now in use have proved reliable and their sensitivity is adequate. THERMOMETERS. For temperatures above -35' F., mercuryfilled thermometers m e setisiactory. It is desirable to have a n open scale, so that differences of 0.05' F. can be read or estinisted easily. For temperatures below -35' F., both toluene-filled thermometers and the newer mercury-thallium type have been used. Scales should be sufficiently open to permit reading, or estimating easily, differences of 0.1" F. The rangeshouldextend above -35" F., so that daily comparisons can be made with mercury-filled thermometer. Toluene-filled thermometers must be kept in an upright position a t all times. All thermometers should be checked for accuracy of scaling by comparison with platinum resistance thermometers or other certified standards. INSULATION. All items of the installation inside the rectangle of broken lines in Figure 1 should be effectively insulated. In the final design, described below, this is accomplished by placing them in an insulated compartment. The exposed portions of copper are protected by a special sponge-rubhcr tubing. OPERATION.Preliminary to operating the equipment, the three baths are filled as follows: Bath 1 (E/, full), 99% isopropyl alcohol; bath 2 full), acetone; bath 3 (full), acetone. Before starting the motors, the two pumps are turned manually through several rotations to make sure they are full of acetone. Bath 1 is then packed with lumps of dry ice of any sise up to that of a baseball. The thermoregulators are adjusted; that for bath 3 as nearly as possible a t the test temperature and that in bath 2, 5" to 10" F. lower. Then with both relays turned to the "on" position, the motors are started. The approximate bime required to bring bath 3 from room temperature down to opcrating temperature is indicated in the following tabulation: Operating Temverature, Bath 3
Figure
P.
Latort Design of Low-Temperature Thermostat
e
Time Starting a t 10-80'
F.
Mi-.
F.
Bath 3 mounted on a ~ p e c i a l l yconrlrudrd cabinet holdins other baths end acCell0,cDI
DETAILS
OF THREE-BATH THERMOSTAT
The characteristic features of the three-bath thermostat me shown diagrammatically in Figure 1.
After coming to the operating temperature, bath 3 usually requires additional acetone to make up for contraction in volume incident to the cooling. When bath 3 bas come approximately to the desired temperature both thermorewlators should be adjusted. The one in bath 3 should be set to hold the exact temDerature desired. and the one
BATH2. The containor is a 10 -2 10 inch'Pyrex jar. The bath liquid is acetone; in addition to a cooling coil similar to that in hath 1 there is a bimetallic thermoregulator and a 250-
temperature to be k a i h s i n e d in bath 3. The acetone in baths 2 and 3 must he replenished to make up.
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watt immersion heater (not shown in Figure 1). BATH 3 The container is a Dewar-type evacuated jar with minimum inside dimensions of 6-inch diameter.and 16-inch depth. The bath liquid is acetone, Immersed in i t are a bimetallic thermorewlator and a 125-watt knife-blade immersion heator (not d : w u m Figure 1). .\~OTURSA N D PUMPS.Motors are of 0.25-horsepower size and
reauired some revamDinp before they m v e satisfactory perform-
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pumps has agreed to supply a t a future date, a special type, designed for acetone and ha&g mechanical seals instead of the composition packing. The pumps must never be allowed to run dry. The shafts are turned bv hand before thev are started until air bubbles cease to come out. MAGNETIC VALVE. The valve is a three-way type with 0.25inch ports. When in closed position, the coil in hath 1 is byDassed but the DUD continues to move the acetone in bath 2. thereby effecting thinecessary stirrinr. --. .
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metallic regulators and a type of relay which makes a n d breaks by the magnetically controlled movement of an iron plunger floating in mercury in an evacuated, hermetically sealed glass tube. There are suitable switches and pilot lights.
ture. This is most rapid when the atmospheric huGidity is high. The insulating efficiency of the unsilvefed jacket of the Dewar flask is not always sufficient to prevent the condensation of moisture on the outer surface of the elass. A stream of air blown over the observation area prevents-this trouble. FINAL DESIGN
The original three-bath thermostat was B typicel chemist's development, spread over the working surface of a fair-sized laboratory bench, and included certain makeshift features which were characteristic of its evolution. After a considerable period of useful though inartistic service, it w a s decided that complete revamping was in order, and an integral, self-contained unit was designed and constructed. The Dewar jar (bath 3) was mounted on a specially constructed cahinet which housed baths 1and 2 as well as motors, pumps, relays, etc. The general appearance of the assembly is shown in Figure 2. It has proved very satisfactory, and detailed information regarding it has already been supplied to several laboratories of the companies served hy the writers' organization. The s a n e information will he furnished, upon request, to interested outside organizations. There is not, as yet, any known commercial source of supply for the complete assembly.
