Aug., 1921 THE JOURNAL.OF INDUSTRIAL A N D ENGINEERING CHEMISTRY 701 -

LABORATORY AND PLANT - Distillation Apparatus‘

By Paul Gross and Alexander H. Wright CHEMICAL LABORATORIES O F TRINITY COLLSGE, DURHAM, N. c.. AND QUEENS UNIVERSITY, KINGSTON, ONTARIO

The different types of apparatus herein described have been devised from time to time to meet experimental situa- tions arising in the course of the authors’ work. For some of these no originality other than that of form is claimed. Their usefulness and simplicity, together with the general lack of knowledge concerning them, is deemed sufficient reason for recording them.

FRACTIONATINQ COLUMN

Anyone who has had to perform the frequent fractional distillations incident to the laboratory preparation of pure organic chemicals has felt the need for a fractionating column which was of good efficiency, and a t the same time strong, simple of construction, easy to make or buy, and which could be quickly and thoroughly cleaned and set up. The still described below answers these requirements.

It consists of a straight tube A (Fig. 1) with a series of small bulbs sucked in on opposite sides, each pair of bulbs lying between the pair next above and below. The bulbs, being thin, permit of rapid heat exchange with the air outside. Their large area, together with the baffling of the ascending vapors by the alternately projecting bulbs, brings about a thorough contact between the liquid as a thin film and the rising vapor. These provide the necessary conditions? for efficient separation.

If made of Pyrex glass and sealed to a flask as shown in Fig. 1, this makes a durable, efficient still. The thin bulbs are well protec- ted. There is a free passageway down through the tube, which makes cleaning and draining easy, and there are no movable parts to lose or break. The cylindrical profile permits of fastening as with an ordinary straight glass tube, with clamps a t appropriate points.3 The symmetrical bulbs will stand the lowest

still available for fractionations in vacuo.4 The efficiency of one of these columns

(Table I) was determined by distilling a mixture of 50 g. each of purified benzene (b.p.80.20’ * 0.05’, f. p. 5.50’) and toluene (b. p. 110.60” * 0.05’) as recommended by

Young.S The weights of the fractions between definite boiling temperatures were determined. The usual correc- tionE for pressure and thermometers were made.

The data are for a tube of Pyrex glass 62 cm. long and 2 cm. in diameter, having 42 pairs of bulbs which approximated to three-fourths spheres of 1 cm. in diameter. This was sealed 2.3 cm. down the neck of a 250-cc. Pyrex distilling flask, and was provided with a delivery tube 4 em. from the

0 pressure without breaking, thus making the

~

1 Received November 23, 1920. 2 Young, “Fractional Distillation,” 190 8 Compare Merriman, J . Chcm. Soc., 99 (1911), 994, who states, with

refereuce to ordinary types of column, *’a long fractionating column is a heavy piece of apparatus, and experience has shown that it is undesirable that any part of its weight should be,borne by a clamp.”

4 Noyes and Skinpor, J . A m . Chcm. Soc., 89 (19171, 2718, describe a fractionating column for distillation

‘ciple of which is the same as that of t 6 Young, LOC. cat., .p. 158.

comparisoq such as that of Rob well have been used here, but f

common forms of column with

S o ~ p other more quantitative method of

TABLE I Roiling Points of Weight of

Fractions Distillate Per cent. of c. Grams Total Distillate 80.2-83.2 83.2-86.2 86.2-89.2 89.2-92.3 92,3-96.4 95.4-98.5 98.5-101.6

101.6-104.6 104.6-107.6 107.6-110.0 110.0-110.6 110.6 110.61

4.587 22.590

7.322 6.086 4.877 3.267 1.931 5.356 5.425 5 .656

17.192 3.938

10.883

4 . 6 2 7 . 3 38 .2 4 5 . 6 51 .8 56.8 60.1 62.1 67 .4 72 .8 78 .6 96.1

100.00 TOTAL WEIGHT 99.100

1 Residue remaining in column.

top. This represents an average column of this type which, though not the most efficient, is yet the handiest for all- round use.

COMPARISON WITH OTHER TYPES OF COLUMNS To obtain a more quantitative comparison between the

various stills, each of the figures for the per cent of total distillate in Column 3 of Table I were plotted against the final temperature a t which the fraction was collected. Curve B in Fig. 2 represents these results, while the other curves represent the results obtained by Young for two of his types of stillhead: Curve C, the rod and disk, and Curve A, the pear. The figures given are for stills of the same length as that used here.

FIG. 2

The broken line DEHFG in Fig. 2 would represent a still which was 100 per cent efficient. That is, the curve would be identical with DEHFG, and the area between them zero. The benzene would all distil a t 80.2’. The boiling point would then rise abruptly to 110.6’ and the toluene would distil ob. In a given case the area included between the first half of a curve and DEH plus that between HFG and the second half is a quantitative comparative measure of the still’s efficiency. The smaller the areas the more efficient the still. The values of these areas from Fig. 2 are given (in arbitrary units) in Table 11.

TABLE I1 Area under Area above

First Half Second Half TOTAL Rod and Disk 2.6998 1.2027 3.9025 Gross and Wright 2.4421 1.1110 3.5531 Pear 2.3016 0.8120 3.1136

As the figures indicate, the efficiency of our column lies

702

between that of the rod and disk and the pear of equal length. It must be remembered that the above column represents

THE JOURNAL OF INDUSTRIAL AND ENGINEERIATG CHEMISTRY Vol. 13, No. 8

second type (Bruhl, Bredt, Gautier) the receivers are rotated' (by means of a lubricated joint or connection) beneath t h e

ra O p G Z ?

,-I -

8 -

1 -

' I

1 -

1 :

H I 1

B

hand) over the usual forms of the lat- - ' ter. It is quick operating, direct read.. - - ing, and simple in construction. T h e - 10-cc. pipet A (closed a t C) is cali-

brated so that volume v between C and H is one-eleventh of the volume V between C and K. At D aleveling tube F a t least 90 cm. long is connec- ted. The side tube B is 30 to 40 cm.

- - -

- -

FIG. 3

one for average use and is not the most effi- cient that could be made of this type. Also it is constructed of different glass.

This method of making a quantitative com- parison by means of the areas under the curves is, as far as we know, given here for the first time, although i t follows logically from Young's discussi0n.l

PROTECTION OF CORKS

It is very often necessary to fractionate liquids, the vapors of which either attack or exert a solvent action on cork or rubber stoppers. The usual methods of wrapping the stopper with tin or silver foil are only oc- casionally successful, and sometimes (as with high-boiling corrosive liquids like chloroacetic acid) fail utterly, necessitating recourse to expensive all-glass stills.

The device shown in Fig. 3 overcomes this difficulty. It consists of a small ball con-

denser which condenses the hot vapor and keeps it from reaching the stopper. If the bulb is blown from Pyrex tubing or other good grade of glass no fear need be enter- tained of its cracking on account of the temperature ex- tremes to which it is subjected. It works admirably, for example, in protecting the lower stopper in the flask in such an apparatus as shown in Fig. 1. .

MICRO-DISTILLING FLASK

Occasion often arises to distil and determine the boiling point of as little as from 0.5 to 2 cc. of liquid. If the liquid is pure the value can readily be determined by the submerged bulblet method.2 In most cases, however, the liquid is a mixture, and it is necessary to separate the constituents and to learn the boiling points of the fractions to aid in their identification. The apparatus shown in Fig. 4 consists of a small bulb, A, about 1 cm. in diameter, with a side tube, B,

sealed to it, which is the inner tube of the condenser C. In the top of A is a narrow well, about 0.5 cm. deep, made by softening the top of the bulb and pushing in with a charred wood sliver. In this well is put a drop of mercury about 1 mm. deep, into which dips the tip of a copper-constantin thermo- ~ o u p l e . ~ The couple is best calibrated in the still by means

FIG. 4 of liquids of known boiling points.

Many attempts have been made to solve the problem of changing receivers in a vacuum distillation without altering the pressure of the system. These are of two types: the first employing a by-pass controlled by stopcocks.4 In the

7 '7-

6 __%p

RECEIVER FOR VACUUM FRACTIONATIONS

1 Lac. cit., 15s. 2 Smith and Menzies, J . A m . Chem. Sac., 32 (1910), 897. 8 Constructed as recommended by White, J . A m . Chem. Sac.. 36 (1Q14),

1868, 2011, 2292, and Adams, Ib id . , 36 (1914), 72. Instead of using an elaborate potentiometer, if great accuracy is not desired, there may be used a millivoltmeter, or better, one of the numerous compact, portable instru- ments now available which utilize the potentiometer principle.

4 Since writing this our attention ha8 been called by Professor A. B. Lamb to a similar piece of apparatus described by Palomaa, Chem.-Ztg., 1902, 337. This method seems, however, to be generally unknown, al- though the only one which will accomplish the desired purpose simply and efficiently.

Aug., 1921 T H E JOURNAL OF IhTDUXTRIAL A N D ENGINEERING CHEMISTRY 703

$v = P V and p =PV/v Also HI = f i - P

By the calibration V/v = 11 . * . HI = P(V/v - 1) .‘ . HI=P( l I - l ) and P = HI/lO

Therefore, the height HI, in centimeters, *

pressure in millimeters. It is obvious that by changing the ratio Vlv the sensitivity of the gage can be changed. Also in a given instrument two or more marks on CH with the accompanying knowledge of the volume ratios will increase the range of the gage. The one described will, however, be found the most convenient for general use, reading to 0.1 mm. or better, up to 30 mm., thus covering the range for most vacuum distillation.

1

is equal to the

The Consistency of Starch and Dextrin Pastes”’ By Winslow H. Herschel and Carl Bergquist

U. S. BUREAU OF STANDARDS, WASHINGTON, D. c. This paper describes a preliminary investigation for the

best method for determining the consistency of starch and dextrin pastes. While the results of tests are given, it is realized that they are approximate, and serve rather to show the value of the method employed than to indicate the exact qualities of the materials.

There are a great many substances which are not fluid enough to run through a viscometer under hydrostatic head, as in the well-known instruments of Saybolt and Engler, and which a t the same time are not hard enough to be subjected to the Brinell test which is used for metals. Thus there are a variety of substances for which no standard method of measur- ing consistency is available, although many tests have been proposed. The term consistency is used to designate the degree of firmness or cohesion, and is applicable both to the viscosity of a liquid or to the plasticity of a plastic solid.

A number of kinds of penetrometer are in use for testing a ~ p h a l t , ~ and other instruments which might be mentioned are the Legler con~istometer~ and the consistency tester of Hubbard and Pritchard.5 It is doubtful, however, whether any of the above-mentioned instruments could be used to distinguish between a plastic and a viscous substance, a distinction which must be made if a clear idea of consistency is to be obtained.

THE DISTINCTION BETWEEN A PLASTIC AXD A VISCOUS SUBSTANCE

The word plasticity is not always used with the same sig- nificance. According to Bingham16 plasticity is a measure of the consistency a t a given time, while, as pointed out by Em- ley,’ the plasticity of plasters and mortars depends upon the length of time during which they can be worked, and “con- sistency has little influence on plasticity.” In this paper the usage of Bingham will be followed, and plasticity considered as independent of the change of,consistency with time. Thus with plasticity, as with viscosity, a constant consistency during the time of test is assumed, although it is admitted that wlth some substances this assumption may be in error. It is known that lubricating greases may be forced through a capillary tube with greater ease the second time than the first, thus showing a softening of the grease as a result of a breaking down of the structure, and undoubtedly this same action may take place with other substances.

The difference between a viscous and a plastic substance may be seen in its behavior when subjected to successive pres-

1 Received March 10, 1921 2 Published by permission of the Director of the Bureau of Standards. a See, for example, Herbert Abraham, “Asphalts and Allied Substances,”

The Dow penetrometer, supplied with a disk insteudof a nee-

4 J Lewkowitsch, “Chemical Technology and Analysis of Oils, Fats

6 P. Hubbard and F. P. Pritchard, Proc. A m . SOC. Test. Materials, 17

6Bureau of Standards, Scicntilic Paficr 278 (1916). 7 I b i d , Technologrc Paper 169 (1920), 21.

1918, 480. dle, is described in Proc A m . SOC. Test. Moteriols, 6 (1906), 501.

and Waxes.” 5th Ed., I , 362.

(19171, 11, 605.

sures of increasing intensity. For a viscous liquid and a given capillary, the flow is proportional to the pressure. With a plastic substance (which may be considered a soft solid) the flow is propartional to the pressure in excess of a limiting amount p , obtained by graphical extrapolation. If it is as- sumed that

p = - 41d d

where f is the “yield shear value,” and I and d are the length and diameter, respectively, of the capillary; and similarly

where F is the shear due to the total pressure P; then, in general, with a viscous liquid flow is proportional to F, and with a plastic substance flow is proportional to F - f.

The practical significance of the yield shear value for material such as paint, which is applied to a vertical surface, is shown by Table I, slightly modified from table given by Bingham and Green.’ TABJ.E I-INFLTJENCE OF CONSISTENCY UPON WORKING QUALITIGS OF

R f WORKING QUALITY O F PAINT

PAINTS, ACCORDING TO BINCHAM AND GREEN RIGIDITY YIELD SHEAR VALUE

Low Low Thin “runny” paint

High Low Thick runny paint. Will probably drag under the brush (“stringy” paste)

Low High Will not run easily, nor will it offer much resistance to the brush

High High Will have good boiy and covering power, and easily stay put”

The yield shear value is thus a measure of the ability of a substance to resist moderate forces, such as the force of grav- ity, and adhere to a vertical surface where a liquid, even when very viscous, would gradually trickle down. Rigidity is the term proposed by Bingham for the property of a plastic solid which corresponds to the viscosity of a liquid; the reciprocal of rigidity is known as the mobility.

When there is a t least a possibility that the substances to be investigated may be plastic, it is necessary to use a plastometer in which the rate of shear may be varied. This excludes from consideration most forms of viscometer, and leaves the choice of an instrument to be made between the variable pressure capillary instrument of Bingham, and some form of rotating instrument, such as those of MacMichael,2 Doolittle,3 Hayes and Lewis14 and S t ~ r m e r , ~ in which the speed may be changed. Since only in the case of the Bingham instrument has the attempt been made to express R and f in c. g. s. units, this

1 Proc. A m . SOC. Test. Materials, 19 (I919), 11, 640. 2 G. St. J . Perrott and R. Thiesen, THIS JOURNAL, 12 (19201, 324;

8 Seaton, Probeck and Sawyer, THIS JOURNAL, 9 (1917), 35. 4 Am. SOC. Mech. E m . , 38 (1916), 626. SE. F. Higgins and E. C. Pitman, THIS JOURNAL, 12 (1920), 587.

W. H. Herschel, Ib id . , 12 (1920), 282.