ANALYTICAL EDITION
86
blocks are graphic comparisons of the total energy between the wave lengths indicated. A marked change has occurred in the shorter wave lengths. The wattage consumed by the lamp can be increased by decreasing the external control resistances. Experiments
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B
C
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Figure 3-Automatic Lighting Mercury Arc A-Plug connector for ammeter D-D.P. switch 260 volts, 20 amp. E-25-Ohm variable resistance E-S.P. snap switch 260 volts, 20 amp. (280feet No. 12 nichrome wire) F-S.P. switch 260 volts, 10 amp. C-High inductance C 1 5 5 - O h m resistance. 2 amp. No. 12 asbestos-insulated copper wire used
were run to determine whether a constant total intensity could be maintained by a wattage increase. Curve B, Section I, Figure 2, indicates the per cent increase over the original wattage required. As shown in Section 11, the re-
VOl. 1, No. 2
arrangement in energy distribution is not marked except after long service, when an actual browning of the lamp tube becomes evident. This browning is probably due to a deposition from the tungsten electrodes. Since simplicity is essential in any maintenance scheme, only the required wattage control without the more involved voltage and amperage factors was determined. The lower original fusion and running temperature may account for the more uniform behavior of the quartz in the special burner, as compared with the &inch clear-quartz burner. Automatic Lighting Mercury Arc
To eliminate the necessity for handling the 20- and 30-inch light units and also to facilitate developing semi-automatic weathering apparatus, an automatic lighting mercury arc has been developeds (Figure 3). The changes are (1) the addition of a positive electrode, I , at the level of the mercury in the well; (2) a high-resistance, G, in this electrode circuit; and (3) a high inductance, C, in the other positive electrode line. A slight quiver of the mercury establishes an arc between H and I which jump$ to J , because of the resistance and the inductance. The circuit through the auxiliary electrode can then be cut.
Coated Spiral Fractionating Columns’ Thomas Midgley, Jr. THOMAS & HOCHWALT LABORATORIES, DAYTON, OHIO
OME time ago it was observed that a Hempel column filled with a material which would behave as a “boiling
S
stone” in the liquid being distilled gave better results than did the customary glass beads. At that time, and without further investigation, crushed antimony was selected to serve in this capacity, because of the ease with which it could be prepared. The present development is an outgrowth of this earlier observation. Comparative Efficiency of Various “Boiling Stones”
It was believed that varying degrees of efficiency might exist among different materials which behave as “boiling stones.” To determine this, the following experiment was conducted: A 2-liter round-bottom flask was mounted beneath a reflux condenser and half filled with a mixture of equal parts of benzene and toluene. A thermometer, reading in tenths of a degree, was placed in the liquid and constant heat applied to the flask. After refluxing started, the temperature was observed until it became constant. This procedure was repeated with various materials as “boiling stones,” with the following results: MATERIAL
No boiling stones
Crushed antimony Crushed porcelain Carborundum cloth Brass strips
borundum cloth and the fractionation of benzene and toluene attempted. The results were quite unsatisfactory. It is believed that this was due to the absorption and holding of a large quantity of liquid by the cloth. Note-Although it would appear that carborundum cloth is of no value in a fractionating column (other experiments have confirmed this), it nevertheless is a very useful “boiling stone.” For example, in a distillation at 20 mm. pressure of a high-boiling, semi-viscous liquid, bumping was entirely prevented by the use of carborundum cloth spirals placed in the liquid, whereas the admission of air through a capillary had not given satisfactory results.
A single spiral column (Figure 1) was next constructed and coated with carborundum. The results with this column were decidedly better than had ever been obtained with either plain spirals or Hempel columns. A multiple spiral column (Figure 2 ) was then constructed and coated with carborundum, and the results were sufficiently good to justify comparative tests. (Figure 3)
TEMPERATURE MATERIAL TEMPERATURE 0 c. oc -. _. Single Spiral Column 94.0 Glass beads 94.0 93.8 Steel strips 94.0 All columns were 92.6 Etched brass 94.0 88.7 Etched steel 94.0 made of metal, because 94.0
It is evident that many other materials may well be investigated in the preceding manner, and it is quite likely that results superior to those obtained with carborundum cloth will be found. A Hempel column was then filled with small scrolls of car1 Presented before the Division of Organic Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928.
it may be fabricated with greater ease than Figure I-Single Spiral Column glass. A single spiral column (Figure 1) is made in the following manner: A piece of 3/4-inchbrass tubing, of the desired length of the column, has its ends closed by silver-soldering brass washers in place. A strip of metal, ‘/8 inch square, is wound on this core to approximately a 1-inch pitch and silver soldered in place. A piece of brass tubing approximately 1 inch in inside diameter, which will I
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 15, 1929
fit snugly, is slipped over the assembly and cut to length. Suitable ends are soldered t o the column to fit thermometers, condensers, and distilling flask. COATING WITH CARBORUNDURI-The column is filled with 8, dilute solution of shellac in alcohol and drained. It is mounted on a standand connected to a source of air saturated with alcohol by placing a wash bottle filled with alcohol in the air line. The air is turned on and blows out the excess shellac solution. After the excess shellac solution has drained from the column, a roundbottom flask containing 60-mesh carborundum is placed in :he air line and so connected to the air supply that carborundum particles are carried from it by the air stream to the column. After a few minutes carborundum p a r t i c l e s come through. The alcohol wash bottle and carborundum flask are removed from the air line and air is blown through the Figure %Multiple column until the odor of alcohol almost Spiral Column disappears from the air as it leaves the column. The column is next mounted for distillation and benzene distilled through it until all traces of alcohol in the distillate disappear. VARIATIONS O F CONSTRUCTION AND COATINeIt is obvious that a column using shellac for a binder is unsuited to alcohol distillations. I n such cases a column using water glass as a binder may be constructed. It is obvious also that for other special purposes better binders may be selected than either shellac or water glass. It likewise is apparent that metal columns cannot be used where corrosive materials, such as strong acids, are to be distilled. However, in the general field of organic research, particularly with hydrocarbons where maximum efficiency in fractionation is essential, metal columns with shellac 8Qi binders are quite ap80 0 plicable. It is sug799 gested that a column m a d e f r o m Pyrex, 788 Li coated with carbor u n d u m sealed to 797 e 796 a the g l a s s , would E 795 have a very wide 2 794 application.
87
soldering is too high for organic binders to stand. Therefore it is desirable t o construct multiple columns with flanged ends, to which the end connections may be bolted after the passages are coated. Adiabatic Coated Spiral Column
The description so far covers only columns designed to replace elementary Hempels. It becomes apparent that if improvements are made on the elementary Hempel column such improvements can be incorporated with the recognized principles used in adiabatic and partial-condensation columns. For this purpose a single spiral column, 4 feet (122 cm.) long, was built and coated. An air space was provided around the column as shown in Figure 4. Ample nichrome heating coils were provided around the air space and the assembly was insulated by asbestos and felt. A thermometer was placed in the air space and during operation was held in substantial agreement with the distillation temperature. The superstructure a t the top of the column was an adaptation of a principle of partial condensation received in private communication from F. H. Rhodes, of Cornel1University. This column was used for the separation of hydrocarbons produced in the destructive distillation of rubber. Components boiling within 4 degrees of each other were detected on the initial fractionation. Three re-runs were required to purify such components suffi- * ciently so that subsequent identifications were made possible. To measure the efficiency Of this Figure &Adiabatic Coated Spiral Column 150 cc. of pure benzene and 150 cc. of pure toluene were mixed and distilled. The over-all rate of delivery was 1 cc. per minute. The distillation curve is shown in Figure 5. Ninety-four per cent of the benzene and 86 per cent of the toluene were recovered, of practically the same purities as were the original materials. The Engler distillations, specific gravity, and freezing point of the recovered materials are recorded in Figure 6. Figure 793 Multiple Spiral 7 represents the results of purifying meta-xylene. 73 2 Column Inasmuch as the “residue” from these columns is larger than could be desired, this type of column does not appear to 79’ M u l t i p l e spirals 7s0 zo Jo 40 5o Bo 70 so are f a b r i c a t e d i n be adaptable for use in separating a component present in Per cent s u b s t a n t i a l l y the small quantities (30 cc.) . Figure 3-Comparative Distillation Curves Same m a n n e r as Comparative Tests of Fractionating Column single spirals, except A column 15 inches (38 cm.) high was mounted with the that larger diameter cores are used and more than one spiral is. wound thereon. The column used for obtaining the results customary condenser and thermometer (reading in tenths of a reported in Figure 3 consisted of a 3-inch core with three degree) on top of a 500-cc. round-bottom flask. Two hundred parallel spirals wound clockwise on it. A thin sheet of copper cubic centimeters of a selected commercial benzene (f. p. covered these three passages. Three counter-clockwise spirals +2” C.) were placed in the distilling flask. The heating were wound upon this, which in turn were covered with sheet rate was adjusted to deliver 2 drops per second from the conmetal and suitable ends silver soldered in place. The column denser. The condensate was collected in 10-cc. cuts and was coated and the whole assembly was insulated with mag- freezing points were determined. At the end of the run the nesia pipe covering and felt, giving an outside diameter of 6 ten cuts of highest freezing points were mixed (in all cases this 100 cc. represented a consecutively delivered cut), and inches (15 cm.). The passages of multiple spiral columns should be coated an Engler distillation was made in an A. S. T. M. gasoline separately, since simultaneous coating fails to give uniform distillation apparatus (standard except that a tenth of a deresults. Separate coating can be done with ease only before gree thermometer was used). Four runs were then made as the end connections are in place. The temperature of silver- follows: OI
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A N A L Y T I C A L EDITION
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Per cent Figure 6-Distillation Data for Materials Recovered from Distillation of BenzeneToluene Mixture i n Coated Spiral Column
Run 1. With a Hempel column filled with glass beads. Run 2. With the same column in which crushed antimony replaced the glass beads. Run 3. With the glass beads coated in the following manner: The beads were wetted with a thin solution of shellac in alcohol and after the shellac had partially dried the beads were shaken with 60-mesh carborundum. After further drying the beads were placed in a round-bottom flask, covered with benzene, and
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20
30
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The resulting curves of the Engler distillation are plotted in Figure 3.
M. G. Raeder NORGSSTEKNISKE HOISKOL,INSTITUT FOR UORGANISK KEMI, TRONDHJEM, NORWAY
D U R I N G laboratory investigations of methods for leach-
1
Received September 8, 1928.
DAY
the whole distilled until all evidence of alcohol in the distillate had disappeared, after which the beads were removed and dried. Run 4. In the coated multiple spiral column, which was the same height as the Hempel column previously used.
Electrically-Heated Thermocirculator for Hot Leaching and Digesting’
ing certain ores, an apparatus was wanted permitting continuous leaching with exceedinglycorrosive, boiling liquids. For this work an all-glass construction as illustrated proved very useful. The apparatus, which is easily made out of a round flask and some glass tubing, consists of a glass bulb connected with a reflux condenser a c t h e top and a circulation tube between the bottom and the upper part. The lower part of the tube is covered, as the illustration indicates, by a layer of asbestos sheet around which a nichrome wire is coiled. This heating coil is insulated and protected on the outside by mica-mantled asbestos fastened with brass caps carrying contact screws and connected with an adjustable resistance. For use the apparatus is filled with preferably preheated leaching liquid to a little below the upper opening of the circulation tube and the current is switched on. Soon a local steam generation drives the liquid into the bulb with considerable force and thus starts a circulation. The material to be leached is then charged through the top opening and the condenser replaced. If the apparatus is of correct di-, mensions, the circulation should not be continuous-as, for instance, in an air lift-but markedly pulsating. In that way not only is the liquid circulated, but-and this is the special feature of the device-the material to be leached is itself brought into vigorous circulation, even when of high specific
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Per cent Figure 7-Distillation Data o n PurMcatlon of Meta-Xylene
directions can be given, different liquids demanding different working conditions. The principle of the apparatus-the leaching matter itself being kept in continuous circula t ion-s h o u l d insure the best possible contact between liquid and solid and thus give a maximum of leaching efficiency. The circulation may be carried on for days without loss of l i q u i d a n d w i t h o u t danger of breakdown, the apparatus being entirely free from moving parts. The apparatus needs no supervision and may be left working during the night
ture.
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