A One-Piece Glass Micro-Kjeldahl Distillation Apparatus PAUL L. KIRK, University of California Medical School, Berkeley, Calif.
D
ESPITE the popularity and increasing use of the micro-
the flask is a trap and head leading to a small glass internal condenser which drains through a vertical delivery tube into the receiver. An overflow and by-pass carry the condenser water either to the drain or to the steam generator, which is equipped with an auxiliary drain tube. The total height of the apparatus is 35 cm. (14 inches). The steam generator jacket is 42 mm. in diameter and 16 cm. in height, the bulb being 60 mm. in diameter. The internal effective portion of the condenser is 18 mm. in diameter and 55 mm. in length.
Kjeldahl method for nitrogen determination, there have been few fundamental improvements of the distillation apparatus originated by Parnas and Wagner ( 3 ) . Their design has a number of inherent drawbacks which are generally recognized. Schulek and Vastagh (4) criticize the use of rubber connections. In some cases these have been replaced by glass joints, but this increased the fragility of the apparatus and rendered it difficult to assemble. Neither did it improve the design with regard to the number of pieces to be mounted and table space occupied. Hoppe-Seyler ( I ) has eliminated a portion of the clumsiness of the apparatus, but has also increased fragility without a large gain in compactness. Since it has been found in this laboratory and elsewhere (8) that condensers of Pyrex brand glass gave results identical to those of silver, a completely new Kjeldahl distillation apparatus was designed. (It was constructed through the cooperation of C. M. Flanders, Box 232, Berkeley, Calif., who can now supply this apparatus in quantity.) Tests of this apparatus showed it to have a number of points of superiority over the usual type of equipment. All rubber connections were eliminated from the distillation train; danger (of breakage was reduced by the strong, compact construction; multiple outfits were easily built up, because of the upright shape and small size; considerably less attention during the course of distillation was necessary; only one burner was used to operate the apparatus and one clamp to hold it in place; very little condensation of steam occurred in the flask; and no diminution in volume took place during distillati on. With a single distillation outfit, the time r e q u i r e d f o r a n a n a l y s i s was not shortened; but, owing to the very slight attention required during distillation, o n e o p e r a t o r could conveniently operate a small battery and save time in this way. Only one precaution was found necessary, i. e., prevention of sucking back of the sample. This was readily a c c o m plished by the p r o c e d u r e described below.
TABLEI. ANALYSISOF NITROOEN-CONTAININQ SOLUTIONS 7
Substance
(NHa)aSOr
Nitrogen
Nitrogen Found
MQ.
M Q,
%
0.2096 0.2082 0.2082 0.2096 0.420 0.417 0.420 0.420 0.783 0.787 0,786 0.785 0.387 0.388 0.387 0.388 0.758 0.761 0.762
-0.2
0.210
0.418
Urea
0.792
pAmino benzoic acid
0,388
p - Amino
0.762
benzoic acid
Error
-0.8 -0.8
-0.2 4-0.5 -0.2 +0.5 +0.5 -1 1 -0.6 -0.7 -0.8 -0.3 0000 -0.3 0000 -0.5
-0.1 0000
Around the steam generator may be wrapped an insulating asbestos jacket (not shown) to prevent sudden cooling from draughts. A few boiling chips of porcelain or silicon carbide are used in the generator to prevent irregular boiling. Silicon carbide chips are superior t o those of porcelain. It was found desirable t o use a moderate flame for the initial heating and a strong flame as soon as boiling started. Only at this point was there any tendency t o suck back. As soon as distillation started, no further attention was necessary. The apparatus was used in a fashion similar to the usual micro-Kjeldahl distillation. The digested sample was rinsed in through the filling funnel, followed by the caustic, with formation of two layers in the flask. With the by-pass and generator drains closed with pinchcocks, the water in the generator was heated to boiling and the steam distillation continued for 5 minutes, after which the receiver was lowered and rinsed internally by heating 1 or 2 minutes longer. The outside of the delivery tube was rinsed into the receiver. On removing the flame, the condensation of steam served to suck the contents of the flask into the generator. This usually required about a minute, and could be accomplished instantaneously by opening the by-pass pinchcock momentarily, thus admitting a trickle of cold water. The flask was rinsed with distilled water which promptly sucked into the generator. The generator drain was opened, followed by the by-pass, thus allowing the condenser water to flush out the generator] an operation requiring only a short time. The apparatus was then ready for the next sample, which could be introduced while the generator was still being flushed. Some typical analyses are shown in Table I. Excellent
Experimental The apparatus, shown in Figure 1, consists of a distillation flask, the bulb of which contains 25 t o 35 ml., inclosed in a glass jacket which serves as a steam generator. ,4 tube sealed inside the flask and opening into the generator leads s t e a m through the solution being distilled. The arm of a Y in this tulbe is sealed through the wall above the generator to the filling funnel. Above
Sample
FIQURE1 223
INDUSTRIAL AND ENGINEERING CHEMISTRY
224
checks were readily obtained, though the absolute accuracy of the method is not notably different from the usual microKjeldahl, since no fwdamental operations are altered. Modifications tending to eliminate inherent errors may be made as easily as with the older forms of equipment. This 71'0rkwas aided by a grantfrom the Research Board of the University of California.
VOL. 8, NO. 3
Literature Cited (1) Hoppe-Seyler, p , A., lMikrochemie, 446 (1931). (2) Kemmerer, G . , and Hallet, L. T., IND. ENQ.CHEM.,19, 1296 (1927). (3) Parnas, I. K., and Wagner, R., Biochem. Z . , 125, 2 5 3 (1921). (4) Schulek E., and Vastagh, G., 2. anal. Chem., 92, 352 (1933).
RECEIVED February 26, 1936.
Laboratory Bubble-Cap Columns of Glass JOHANNES H. BRUUN, Sun Oil Company Research Laboratory, Norwood, Pa.
This paper contains a description of two all-glass bubble-cap columns of a greatly improved design. These columns are exceedingly easy to operate and may be used for vapor velocities up to 31.3 and 65.5 cm. (1.0 and 2.2 feet) per second, respectively. Since the height of the equivalent theoretical plate of one of these columns is about 2 cm., it is now feasible to build columns with separating powers equivalent to between 100 and 150 theoretical plates in a laboratory of average height.
I
N PREVIOUS papers (2, 3) various all-glass bubble-cap
columns for laboratory use have been described. These columns have been used extensively for many years by a variety of different laboratories and have been found exceptionally valuable, particularly for distillations of mixtures containing organic compounds that tend to undergo decomposition or chemical changes under the catalytic influence of metal packings. Since the time of the last publication it has become apparent to the writer that important improvements in the efficiency of these columns could be made if the height of the
ipgpl
22
ao
20 IO.
FIGLIRE 2. REDESIGNED BUBBLE-CAP COLUMN, 4 - c M . SECTIONS Slots in bubble cap as shown about 0.5 to 1 mm. wide and 5 mm. deep, Lt an anel; of 30' with radius, firepolished. Material Pyrex laboratory glass. All dimensions are in millime(ters. Exact dimensions are circled.
individual plate sections could be reduced without a corresponding sacrifice in vapor velocity.
Reconstruction of the Bubble-Cap Column
NOTE CURVATURE
22
20
ao
In
FIGURE 1. REDESIGNED BUBBLE-CAP COLUMN, 2 - c M . SECTIONS Slots in bubble cap as shown about 0 5 to 1 mm. wide and 3 mm. deep a t sn'angle of dOo with radius fire-polisbed. Matekial P h e x laboratory lass All d i r n h i o n s are in dillimeters. Exact %ime&ns are circled.
A series of short (2-plate) experimental columns having the same internal diameter, but of different designs and dimensions, was made up successively, and tested with respect to vapor velocity, holdup, plate efficiency, ease of operation, etc. The data obtained during the operation of these experimental columns have led to a complete redesign of the glass bubble-cap column, with the result that the degree of separation (number of theoretical plates per meter) now obtainable by columns of the new design is up to 400 per cent as high as that obtained with the old column of the same height and diameter. Detail drawings of the redesigned bubble-cap columns are given in Figures 1 and 2. While these figures represent columns containing only three plates each in addition to the liquid seal customarily used between the still pot and the column, any desired number of plates may be added to the columns. Readers who are not familiar with the working principles of these columns are referred to the earlier paper (3).
