ANALYTICAL EDITION
SEPTEMBER 13, 1938
531
TABLEI. AKALTTICAL RESULTS Compound
Theory
Found
Difference
%
%
%
Carbon tetrachloride
92.20
-0.28
Chlorobenzene
31.5%
p-Dichlorobenzene
48.26
Tetrachlorohenzene
6.5.70
91.92 92.12 91.97 31.52 31.6i 48.21 48.20 66.64 65.45 20.89 20.82 37.31 37.49
p-Chloroaoetanilide
20.91
p-Bromoacetanilide
37.34
a
Theory
:Found
%
70
%
p-Chloronitrohenzene
;!2.52
22.56 2!2.27
T O . 04
-0.23 0
Methyl a-phenyl-8-bromo-Bbenzoylpropionate
:'3.03
23.03 :!3.10
0 f0.07
-0.08
Methyl a,v-diphenyl-a. B-dihydrosps-chlorobutyrate
11.06
2,3.4.6-Tetrachlorophenylhenzoate
42.34
Hesachlorohenzene
74.72
11.03 10.83 42.39 42.41 i4.9'35 i4.85a
-0.03 -0.23 I-0.05 f0.07 f0.26 +0.13
75.024 74.83"
f0.11
-0.08
fO. 15 -0.06 -0 OB -0.26 -0.02 -0,OQ -0 03 T0.15
Compound
Difference
-0.25
+o.m
l i m e contained 15 per cent calcium nitrate.
analyzed in this laboratory, the lime ignition method is known to be applicable to them, with some special precautions ( 3 ) . Experiments are now in progress to test t'he usefulness of the method on a semimicro scale. The analytical results in Table 1 represent the usual accuracy of the method. The repuhtion of hexachlorobenzene as one of the few substances not completely decomposed by lime ignition (3) Tvas confirmed when the usual procedure gave results as much as 2 per cent below the theory. The difficulty is Pasily owrrome hp mixing 15 per cent of powdered
anhydrous calcium nitrate with the lime, and the figures qhown in Table I were obtained in this way.
Literature Cited (1)
Caldwell, J. R., and %foyer, H. V.. 1x0. ENG.r r i E l f . , Anal. Ed.,
7, 38 (1935). (2) Delbridge, T. G., A m . Chem. J., 41, 396 (190'9). (3) Meyer, Hans, "Analyse und Konst,i~utionsermittlungorganischt. Verbindungen," 4th ed., p. 253, Berlin, Juiius Springer, 1922 (an excellent discussion of t h e l i m e ignition method). R
E
C
~
,Tune I ~ 21, ~ ~1938 ~
Improved Method of Heat Input Control in Glass Fractionating Columns G. H. MOREY, Commercial Solvents Corp., Terre Haute, Ind.
T
HE kettles of all-glass analytical columns are usually
heated by an oil bath or, electrically, by resistance wires which are immersed in the liquid and sealed through the walls of the flask. This is usually satisfactory for small quantities of material which are fractionated for analytical purposes only. Occasionally it is necessary to use an all-glass column D C for preparing large a m o u n t s of p u r e compounds for use in other work. If the kettles are glass flasks of 5 - l i t e r c a p a c i t y o r over, heating by means of an oil bath is undesirable because such a large quantity of hot oil constitutes a fire hazard, accurate heat input is diffic u l t , a n d if t h e column floods it is
1
KETTLE
difficult to remove the source of heat from the kettle quickly. Heating large volumes of liquid (of the order of 10 liters) by electrical immersion heaters is impracticable for several reasons, chief among which is the desirability of heating the flask over its entire surface in order to prevent undue condensation of the vapors before they can enter the column. The method of heating described herein mas designed to overcome these difficulties.
Apparatus The column proper Tas of Pyrex glass, 3.12 cm. (1.25 inches) in inside diameter and 150 cm. (5 feet) long, and was packed with the single-turn glass spirals developed at the Pennsylvania State College. The heating jacket for the column was a Pyrex tube 55 mm. in inside diameter and 150 cm. (5 feet) long, wound with Xichrome wire in two sections of 500 watts each. The outer jacket was a Pyrex tube 71 mm. in diameter and 150 cm. ( 5 feet) long. The construction of the column followed conventional deaigns. The kettle (Figure 1) was a 12-liter flask fitted at the top with the female part of a 40/50 ground-glass joint which was attached to the bottom of the column. .4 24/40 ground-glass joint was sealed into the flask about 7.5 cm. (3 inches) from the top, for the purpose explained below. A mantle of thin asbestos cloth was sewed about the flask with asbestos thread. Then another mantle of heavy asbestos cloth was sewed over the first. Patterns were first cut from ordinary cloth to determine the size and the best method of cutting to avoid wrinkles. The mantles before sewing on to the flask looked like Figure 2.. In the second mantle, Nichrome wire was sewed spirally around the flask from the bottom up. The distance between each turn was about 0.94 to 1.25 cm. (0.375 to 0.5 inch). In this may three circuits of 500 watts each were sewed around the flask: one at the bottom, one around the middle, and one around the top side. Each circuit was controlled by a Variac. The first mantle prevented the hot wires from touching the flask at any point. The heating wire was then insulated against excessive radiation losses by winding asbestos rope around the
INDIJSTRIAI, AND EYGINEERING CHEMTSTR'1
k, FIGURE 2. ASBESTOSMANTLE
c'
flask from the bottom u Each turn of rope was held against the flast by pieces of asbestos thread tied into the mantle at one or two points. Another mantle of mbestos cloth was then sewed over the outside. The terminals of the heating units were silver-soldered to copper strips 1.25 X 5 cm. (0.5 X 2 inches). These heating units were then connected to the source of current by battery clips which were insulated from one another by drawing short pieces of rubber tubing over them. With this arrangement, the kettle could be quickly disconnected for cleaning. In order to hold the kettle against the groundglass joint at the bottom of the column, a cradle of wire netting shaped like a half sphere was made. The lower half of the kettle rested in this cradle and springs suspended from a circular iron standard mere connected to the cradle. The tension of the springs held the kettle and contents against the bottom of the column. An iron ring clamped around the top of the kettle prevented too much pressure against the ground-glass joint as the flask became empty. The springs n-ere of the type used on screen doors and were 1.25 em. (0.5 inch) in diameter by 12.5 cm. (5 inches) long. Twelve of these springs were used. S o trouble during beveral months of operation has been experienced because of freezing of the ground-glass joint. The smaller ground-glass joint sealed into the flask about 7.5 cm. (3 inches) from the large ground-glass joint was provided for filling the kettle and to permit observations within the kettle during operation. A &volt flashlight bulb, the lead wires of lvhich were enclosed in a copper sheath, could be lowered into the long glass tube at A (Figure 1) extending to the bottom of the kettle. Looking down through the top of the kettle, it was possible to see when the bulb dipped below the surface of the liquid. A scale on the copper sheath then indicated the number of liters still left in the kettle. In order to prevent the column from being pushed up through the heating jacket as the flask became empty, a flat aluminum disk, D , was placed at the bottom of the jackets. Beneath this disk some asbestos tape-was wound around the column and over this a clamp, C, was tightened. This clamp w.as of the type used to tighten hose connections in automobile radiators, The complete assembly of the kettle is sh0n.n in Figure 3.
Discussion This method of heating the kettle permits of very accurate heat input control. Once the Variacs are set a t the desired points, the column will operate for hours with no attention during the time that one constituent is being fractionated out. It is desirable to wind a 12-liter flask in three circuits so that, as
V O L 10, NO. 9
the liquid level becomes lower, the current in the upper circuits can be diminished, preventing superheating of the vapors. The major portion of the heat can then be furnished where it is needed most-vie., at the bottom circuit where the heat for boiling the liquid is absorbed. This effect can be accomplished in one circuit for flasks of 1-liter capacity by allowing a greater distance between turns of the Sichrome wire toward the top of the flask. The asbestos cloth and sewing cord used in the construction may be urchased from the Johns-Manville Corporation. The grades otcloth are designated as follows: No. 1067 asbestos cloth, 0.08 cm. (0.03 inch) thick, No. ME3010 asbestos cloth, and KO. 285 asbestos cord, 0.16 em. (0.062 inch) thick. The Variacs are purchasable from the General Radio Company, Cambridge, hlass.
It is well to have the joints sealed to the larger flasks a t glass-working shops which are equipped for thorough annealing of such large pieces.
1?1GURE
3.
COMPLETE KETTLE&3SEMBLY
rrrove11 glass fabrics would probably serve rlluch better than asbestos cloth. It is possible that the seams of such fabrics could be fused together with a blow torch instead of by sewing. Since round-bottomed flasks are made up to 22-liter capacity, it is possible to construct all-glass columns of nearly semicommercial proportions using kettles heated in this manner. RECEIVED ~~l~ 6, 1938.
