834
T H E J O U R N A L OF I N D U S T R I A L A N D ENGILVEERING CHEMISTRY
A COMPARBON OF THE RELATIVE EFFICIENCY OF LABORATORY REFLUX CONDENSERS B y M. V. DOVERAND J. W. MARDEN Received June 23, 1916
Further than statements based upon qualitative separations, such as t h a t made by ClOweS,l in which he mentions t h a t there is a considerable loss of ether when it is heated under a Liebig condenser used as a reflux, there has not been, so f a r as is known t o the authors, any 'Ystematic Of the efficiency of different kinds and lengths of condensers. Much important chemical work demands t h e use of this apparatus, and it seemed worth while t o compare t h e efficiency of those most commonly used. The aim Of this work is not to Obtain great accuracy Of results, but rather t o gather data under the ordinary laboratory conditions which will aid in t h e choice of a reflux condenser, when it is necessary t o heat a lowboiling liquid for some length of time. When fat is extracted by means of a Soxhlet apparatus, t h e ether is boiled for about 16 hrs. Should t h e condenser used show a n efficiency of 98 per cent per hr. ( t h a t is, if z per cent of the total ether were lost in I hr.), '/3 of t h e total ether used would be lost in the experiment. It is very obvious t h a t a n efficiency of even a fraction of I per cent per hr. in the condenser is well worthy of consideration. Not long sincej one of us was asked to select a condenser f o r use -,ith the soxhlet apparatus and no preference could be given. Many indeed are t h e claims for great efficiency of the various types in use. that time the various kinds at hand were roughly tested, using gasoline as the volatile liquid. One hundred grams were boiled for I hr. under different condensers. The Source of heat was then removed the flask allowed to cool and reweighed. The efficiency of the condenser was calculated as t h e per cent of gasoline remaining after t h e experiment. TABLEI-l3FFICIENCY
OF REFLUXCONDENSERS (GASOLIIFE) Gentle Boiling. Flow of Water 375 Cc. per Min. Temperature at inflow = 20° C.: at outflow = 24' C . Ball AIR CONDENSER CONDENSERAllihn Liebig Metal Allihn -LiebigGlass Block Tin Length,cm..... 30 80 . . . . 15 48 40 150 100 (coil) Efficiencyperhr. 98.69 9 7 . 6 4 9 6 . 8 9 4 . 6 5 9 1 . 9 6 8 9 . 4 86.4 42.6
I t is apparent t h a t t h e length of t h e condenser makes considerable difference in its efficiency. I n order t o condense any large proportion of the gasoline vapor, t h e longest of t h e Allihn or Liebig condensers must be used. This method of comparison is, however, too crude, and in order t o obtain results t h a t show cornparative values of t h e various condensers now on the market, more accurate meth0d.s of work were devised. Experiments were made comparing t h e refluxing efficiencies of t h e following kinds and lengths of condensers: Liebig, j lengths; Allihn, 3 ; Spiral, 3 ; Hopkins, 2 ; Davies, 3 ; and Friedrichs, I . The simpler form of t h e last named variety was used, not t h a t having a n outer as well as an inner water jacket.2 I n each determination, 100 g. of liquid were boiled in a 2 5 0 cc. Erlenmeyer flask standing upon a concave 1 2
J . Sac. Chem. Ind., 16 (18973, 9 i 9 . Z. angcw. Chem.. 23 (1910) 2425.
Vol. 8, No. 9
asbestos wire gauze and heated from beneath by means of a ring burner. This burner and gauze insure equal distribution of heat upon the bottom of t h e flask. After boiling for '/z hr., t h e burner was removed and an asbestos board slipped under the flask. It was allowed to cool for min. before weighing, t h e water floTving through the jacket. ~ ~ determinations a,ere made in every case. A Woulfe bottle, carrying a thermometer, was placed between the water tap and the condenser, so t h a t t h e temperature of t h e water flowing through the jacket might be observed. This temperature during all of these experiments did not vary than about 3 o (from I6 to 1 9 0 c.), The water was allowed to flow at the rate of approximately 5oo cc. per min. The rubber stopper cafrying the condenser was covered with tin foil to prevent any solvent action by the
It was found necessary, in every case, to bevel the lower end of the condenser tube so t h a t t h e size of t h e drop and t h e rate of drop-back might be kept more nearly uniform. It was also found early in t h e work t h a t the only way in which comparable results could be obtained, was to count t h e drop-back of t h e liquid used, as a measure of the rate of boiling. The Liebig, Spiral and Allihn condensers were kept in a vertical position. The Davies, Friedrichs and Hopkins varieties were inclined slightly, because in these types t h e vapor traverses a space between an inner and outer jacket: this construction caused a drop-back when the condensers were held in a vertical Position, both from t h e bottom of t h e inner jacket, and from the end Of the tube* By the whole apparatus, this drop from the bottom Of the inner tube is made t o fall upon t h e inner surface of t h e Outer tube and down to the tip, thus making t h e drop returning t o t h e flask more nearly of t h e same weight as t h a t in the case of t h e other condensers. I n order t o obtain sufficiently accurate values, it was found necessary t o Correct for t h e amount Of liquid remaining in t h e condenser after cooling. 'TO estimate roughly t h e ether adhering t o t h e walls of t h e tube, it was boiled under a reflux condenser which h a d been previdusly dried and weighed. (No water was allowed t o flow through t h e jacket during these determinations.) When t h e vapor escaped freely from t h e top, t h e flask was allowed t o cool for 5 min. and t h e condenser was again weighed as rapidly as possible. The sources of error in this crude method of procedure are a t once obvious. The results given below are taken into account in Table V and seem sufficiently accurate for practical purposes. TABLE 11-CORRECTIONSBOR ETHERI N VARIOUSCONDENSERS
Ball Fried(Coprichs ,---Davie---LiebigSpiral Allihn per) Length, cm, 15 19 30 15 20 32 9 2s 29 0.07 0.06 0.07 0.06 0.01 0.03 0.09 0.06 0.04 0.06 i.'7 Ether. g.
CON-
DENSER
A few trials were made, allowing the four liquidswater, chloroform, alcohol and ether-to drop back in equal quantities by volume. The number of drops
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Sept., 1916
giving t h e same volume a t t h e temperature of t h e boiling point of each were calculated from t h e respective surface tensions a n d densities given by Castell Evans',using t h e formula given by Findley.2 or, NP= Vld2Nl Nld2' V2dl where Vi and VZ = surface tension; N2 and N1 = no* drops; dl and d2 = densities. I t is evident t h a t different liquids could not be compared in t h e same condenser by using t h e same rate of drop-back in each w e . T h e size of t h e drops is different for each liquid a t a given temperature, t h e attraction of t h e glass varies, etc. Five drops of ether perlsecond were here taken arbitrarily as a standard andA,the number of drops of t h e other liquids having the same 'Ompared to this. These numbers are included in Table 111.
-VI - r"&I
vz
TABLE 111-EFFICIENCY WITH DROP-BACK I N EQUAL QUANTITIESB Y VOLUME(LIEBIGCONDENSER) No account was taken of the quantity of substance adherin!: to condenser tube Drop Rate PER CENT EFFICIENCY B. P . 20 cm. 20cm. 24cm. 38cm. SUBSTANCE O C. Jacket Verylow 98.4 98.76 Ether.. 34 5 93.6 88.5 98.16 61 7.6 Chlorofo 9 7 . 9 9 8 . 5 98.42 78 4.5 Alcohol.. , 98.78 99.0 99.42 Water.. 100 1.77
. . ... .. .. .... ..
The percentage efficiencies in Table 111 indicated too great a n apparent loss in t h e case of chloroform. Ether, boiling as it does a t a lower temperature, would be expected t o escape in larger quantities if conditions were in every way comparable. When i t was found t h a t correct results could not be obtained b y refluxing equal volumes of t h e respective liquids, a comparison was made by weight. I n order t o determine t h e number of drops of each liquid having t h e same weight, t h e respective weights of one drop of each were determined, t h e temperature being as near t h e boiling point as was practicable. Twenty drops were in each case drawn from a given orifice and weighed. The weight of one drop of water, divided by t h e weight of one drop of any of t h e other liquids, gives the number of drops Of each having the same weight. These appear in IV7 '7 TABLE IV-RELATIVE EFFICIENCY O F LIEBIGCONDENSERS O F DIIIFERENT SUBSTANCE Water. . . . . . . . Alcohol.. . . Chloroform Ether ...... .
.....
LENGTHS DropPER CENT back B. P . 15 cm. 2 0 c m . 1 100 98.8 98.17 2.5 78 97.3 97.9 2.3 61 97.0 97.3 . . . 3 . 3 4 34 94 94.3
EFFICIENCY 24cm. 99.15 98.9 98.8 96.4
37 cm. 99.42 98.4 99.0 97.0
Table IV shows t h e influence of t h e length and also t h e influence of t h e boiling point of t h e liquid upon t h e efficiency of t h e Liebig condenser. As would be expected, t h e longer t h e condenser, and t h e higher boiling t h e liquid, t h e greater t h e efficiency. It is noteworthy, too, t h a t t h e values are very largely dependent upon t h e rate of boiling. There are many sources of error in t h e above method. A small error in counting t h e rate of drop-back may account for t h e irregularity in t h e efficiency of t h e 37 cm. Liebig shown in Table IV for chloroform. There is also a n 1 "Physical Chemical Tables." 2 (1911), 725, Chas. Griffin & Co., London. * "Practical Physical Chemistry," 1914, p. 94, Longmans, Green & Co., New York.
83 5
irregularity in this table in the values for efficiency in t h e case of ether. Slight changes in external conditions such as draughts, etc., cause considerable variation in t h e efficiency of t h e shorter condensers. I t was found by trial, t h a t if a small plug of glass wool was placed in t h e upper end of t h e 2 4 cm. Liebig, t h e efficiency was changed from 96.4 per cent up t o about 98.7 per cent. Considerable saving of ether in t h e Soxhlet or similar apparatus can be effected if air currents are prevented, as these which carry away t h e vapor, The relative efficiencies of a number of condensers have been at two different rates of dropback, v i z . , 3.3 and' s drops per second, Results at the latter rate are given to show that with a rapid rate of boiling t h e very short condensers cannot, be used t o advantage. As might be expected, our results checked best a t t h e lower rate of drop, partly no doubt because i t is rather difficult t o count accurately, drops a t t h e rate of 5 per second or 2 5 in j seconds. The results in Table V express t h e total c o n d e n s i n g e f i c i e n c y of t h e condensers enumerated. TABLEV-A
COMPARISON OF RELATWEEFFICIENCY OF VARIOUS KINDS OB CONDENSERS FOR ETHER
Rate of Drop-back, 5 drops per second Length Per cent Cm. 8fficiency Hopkins
z[$y,ichs
37
99.03
Price
Rate of Drop-back, 3.3 drops per second Length Efficiency Per cent CoNDEKsER
$3 t o s 4 ( ? ) Hopkins
98.98 98.87 $$1.20 5.00 $2.40 98.80 98.14 $6.00 98.02 $1.75 Hopkins 97.74 $1.50 Allihn 97.64 $5.00 D.av!es 97 63 1 00 15 97:0(?) $%:SO 97.16 $1.20 20 16 97,1z $1,35 9.5 97.0(?) (a) 96.64 i3:ZO 20 73.23 $0.75 15 0.00 .... ( a ) Drop-back 3.2 per second. Highest condenser.
g;:;:
37 l8 25 30 27.5 29 20 32
Graham Allihn Allihn Friedrichs Graham Hopkins Hopkins Graham Liebig Liebig Liebig Liebig Liebig
30
98.82
29 9.5 20 18 16 27 37 25 32 37 20 15 20
998.60 8.7 98.58 98.5 98.5 98.48 98.4 98.3 98.17 98.0 97,86 97.78 97.60
rate attainable with this metal
The weight of a drop of ether in the of the copper ball condenser was not determined. Apparently i t is larger t h a n in the case of glass tubes; t h e r e f o r e ,t h e efficiency of this condenser may be greater t h a n is a t first sight apparent, i. e., t h e ether may be boiling much fasterthan is necessary to obtain, in t h e case of glass, a rate of j drops per second. Evidently, at a slow rate of boiling t h e lengths of these condensers is of little moment. The rate of boiling, rather t h a n t h e length or kind of condenser, seems-to be t h e determining factor in efficiency. CONCLUSIONS
I-It has been found t h a t in order t o obtain comparable results, t h e r a t e of drop-back of t h e liquid must be in approximately equal weights per second. 11-In order t h a t drops of equal weight may return t o t h e flask t h e end of t h e condenser tube must be bevelled so t h a t the drop returns from one point only. 111-The rate of boiling has very marked influence upon t h e efficiency of t h e condenser. IV-The bore of t h e condenser tube has influence upon t h e efficiency of the condenser, as has also a
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T H E J O U R N A L O F I N D U S T R I A L A N D Eh’GINEERING C H E M I S T R Y
narrowing a t the tip or a constriction anywhere in t h e tube. (Noticed in t h e spiral type where t h e spiral is fused on t o t h e inner tube.) These conditions t e n d t o cause choking and when this occurs the loss is always disproportionately great. TT-The length of the condenser is a factor in its efficiency (especially in t h e case of the Liebig) for lowboiling liquids. I n t h e case of t h e other forms t h e length of t h e jacket has less influence t h a n seems t o be commonly supposed. VI-In experiments where a long condenser can be conveniently used, the Liebig seems t o be preferable because it is a much less costly condenser and can be easily cleaned. Where a short condenser is required, the Friedrichs seems best. I‘II-The short Liebig or Allihn can be used t o advantage only when t h e rate of condensation is not greater t h a n from 2 t o 3 drops per second, or when some means is used, such as a glass wool plug in t h e top of t h e condenser or a test t u b e inverted over t h e t o p of t h e condenser t o prevent too rapid a carrying away of t h e vapor b y air currents. DZPARTMBNT OF CHEXISTRY UNIVBRSITY OF MISSOURI,COLUMBIA
CHAIN SCREEN DOORS BY HEXRYH
q’II4GAND
Received June 14, 1916
lTThenever t h e ordinary door of a n oven or furnace is opened a stream of intensely heated gases pours out of t h e upper part of t h e opening, while a t t h e bottom a n equivalent volume of cold air rushes into t h e furnace, chilling contents and walls, entailing damage thereto and loss of heat. Time is also lost, as t h e interior must again be raised t o the requisite temperature. Many makeshifts have been devised t o avoid t h e adverse conditions arising from t h e opened furnace door, b u t until t h e advent of t h e ingenious Wiegand chain screen door, nothing properly served the purpose. What was demanded was a door or shield t h a t would permit a clear, unhampered view of the interior of t h e furnace or o r e n ; would not in any way interfere with t h e free manipulation of t h e tools required t o care €or t h e interior; yet a door t h a t would keep t h e heat in and the cold air out; in other words, a door which should possess a t t h e same time t h e qualities of opaqueness, transparency and penetrability. This was a seeming impossibility until t h e chain door was devised b y a Baltimore inventor. These chain screen doors, in the form used mostly around metal, glass and chemical furnaces, consist of a multitude of freely hanging individual strands of steel chain suspended close together from a bar in a manner t o form a continuous sheet or curtain of chain, not unlike t h e familiar Japanese screen. This curtain of chain, hung before the uncovered opening t o a furnace and looking like a coat of mail, effectively hinders t h e heat, glare, gases and sparks from leaving t h e furnace and checks t h e entrance of cold air. The loosely hanging strands of light chain are parted with ease and pressed aside by t h e tools or other objects projected
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into t h e furnace, only t o fall together again when entrance has been effected. The interstices in the links of chain permit a n unhampered view of t h e interior-in fact a better survey may be obtained t h a n under ordinary conditions, as the glare is toned down and t h e effect is similar t o looking into a furnace through a piece of wire gauze. This is particularly noticeable with those installed on electric furnaces. In some plants, when it is necessary t o work in front of t h e naked fire, the workmen are obliged t o stand back a great distance from their work and protect their bodies from the heat and glare with large sheet-iron shields which are supported b y one hand while t h e other manipulates the tools. This seriously handicaps the workman and. cuts his efficiency in half. I n some industries t h e men are obliged t o protect their eyes with dark goggles and their bodies and hands with extra heavy coverings. All such devices impede the men in the performance of their work. I n those plants where %he new chain screens have been employed the workman has both hands available for his work and may, with comfort, Ercely manipulate his tools while standing within n fewinches of his work. I n glass working, t h e heat of the uncovered furnace is intense. Measured on the thermometer it shows a temperature of 600 t o IOOO’, yet when one of these chain screens is placed in front of t h e opening the temperature is lowered t o such an extent t h a t the bare hand may be held without danger or discomfort within an inch or so of t h e protecting transparent screen. I n a boiler room where t h e Wiegand chain doors have been employed for about three years, experiments were made t o obtain a n idea of the effectiveness of the device in avoiding t h e losses arising from t h e frequently opened stoking door. A thermometer was fixed on a standard in t h e fire room a t a point opposite this door and I O in. therefrom. This position was chosen as being near t o the one usually taken b y the fireman when stoking or cleaning t h e fire. When t h e ordinary fire door was thrown open a n d t h e incandescent fire bed exposed, as is t h e case whenever t h e furnace is coaled or cleaned, the thermometer rose t o 400’ F. On covering t h e furnace opening with t h e auxiliary “chain door,” t h e temperature dropped t o 1 3 j o F., and the bare, unprotected hand could be held anywhere in front of the screened opening without discomfort. This drop of 26j’ on t h e application of the screen indicates t h a t a great quantity of heat lost by radiation and convection, through the ordinary uncovered furnace opening, may be saved by t h e employment of such a device. These chain screens have a great field of usefulness in connection with glass furnaces, porcelain ovens, pyrites roasters, chemical, shrapnel and annealing furnaces, and cupolas for melting iron and other metals. Their use around t h e electric furnace has added much t o the comfort of t h e operatives, when pouring. Chain screen doors are supplied in “automatic” and “non-automatic” forms. The automatic is employed
