Aug.9
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
1915
table on page 688. Only t h e corrected figures a n d legends are recorded: reference is made t o both publications, t h e first number being t h a t assigned in Bulletin 94, a n d t h e second, t h e Bureau of Soils number assigned in articles which appeared in THIS JOURNAL.^ T o report in t h e conventional manner t h e results obtained i n t h e examination of t h e various brines submitted for analysis was a concession t o t h e supposed wishes of t h e laymen interested t o whom t h e statement of results as ions conveys b u t slight information. This concession was made against our best judgment, since t o report t h e various basic a n d acid radicles as combined is t o abandon for t h e moment t h e best conception of t h e state of salts in solution. T o calculate such analytical d a t a t o t h e saline combination is t o juggle figures. As t h e basis for t h e conventional combination t h e respective solubilities of t h e component salts, which anciently were regarded as entities, have been taken. This, likewise, is a false basis, since t h e I LOC.
cit.
689
solubility of each salt when alone in solution is different from i t s solubility when in solution with t h e other salts. T h e latter solubility is determined b y t h e equilibrium conditions obtaining for each system studied. T h e conventional combinations should represent, if anything a t all, t h e solids precipitated on evaporation from t h e system studied, a n d should be recorded i n the order of their precipitation. This could be determined only b y a n examination of t h e system under consideration. T h e value of t h e results previously published is scarcely diminished b y t h e errors introduced in t h e calculations previously published. However, t h e fact t h a t t h e system of calculation from ionic t o saline form is based on erroneous conceptions a n d therefore itself is erroneous does not excuse avoidable errors in t h e application of t h e system. For t h a t reason i t is desired t o substitute t h e recalculations herewith presented. BUREAUO F S O I L S . U. s. DEPARTMEXT OF AGRICULTURE WASHINGTON
LABORATORY AND PLANT A MODIFIED BURETTE CALIBRATING PIPETTE AND CERTAIN POINTS IN THE USE OF SUCH INSTRUMENTS By C. W. FOULK Received March 23, 1915
Some months before this article was prepared for publication, t h e writer was told b y t h e “Trouble Man” of a large chemical firm t h a t t h e laboratory a n d factory control difficulties he was called upon t o adjust were frequently caused b y inaccuracies in t h e volumetric ware employed, a n d he added t h a t in his opinion many young chemists a n d not a few old ones were unaware of this source of error. T h e “Trouble Man” must t a k e t h e responsibility for his statement about chemists, b u t t h e author is willing t o testify regarding t h e general depravity of uncertified volumetric ware. During t h e last t e n years t h e calibration tables of several hundred burettes have been examined a n d errors of 0.1 cc. or more have been found t h e rule rather t h a n t h e exception. Occasionally t h e corrections reach a truly surprising value. For example, a t least three otherwise innocent looking burettes have been found with errors of over 0.4 cc. in t h e first 2 0 cc. of t h e scale. It, therefore, cannot be too strongly emphasized t h a t all such measuring instruments must be calibrated before using. If only one or t w o burettes are t o be examined t h e method of weighing t h e water delivered from successive intervals is t h e simplest since i t involves no special apparatus. If, however, a larger number are t o be calibrated or if from time t o time a few must be tested, some form of calibrating pipette will be found a n advantage on account of t h e time saved a n d t h e simplicity a n d directness of t h e procedure. Several such pipettes have been described2 b u t in every case ’
1 Pipettes of the design described in this article and piovided with a ’ 0.01 cc. division scale on the upper stem can be secured from the KauffmanLattimer Co.,Columbus, 0. 2 Arndt, Cenlralblaf, 1856, p. 865; Scheiblei, J . pvakt. Chem., 7 6 ( 3 8 5 9 ) , 177; Ostwald, Ibid., N. F., 25 (1882), 452; Morse and Blalock, A m . Chem. J . , 26 (1894). 479.
a n important point has curiously enough been overlooked, namely, t h e use of t h e two-way glass cock as a n automatic zero adjustment. A modification employing this time-saving scheme will be described in this paper a n d in addition t h e general principles a n d procedures involved in t h e use a n d calibration of these calibrating pipettes will be given. It so happens t h a t in previous articles there is not very good agreement as t o t h e details of determining t h e capacity of t h e pipette itself a n d in some cases t h e methods of calculating t h e final values obtained for t h e different points on t h e burette scale are unnecessarily long. M a n y recent text-books also d o not refer t o t h e use of such calibrating instruments and, therefore, there is perhaps some justification for presenting in t h i s place a more complete account of their ‘ advantages a n d use. T h e i n s t r u m e n t ‘ illustrated here is in its general operation like others t h a t have been described, i. e., i t is a device for accurately measuring successive portions of water as they may be drawn from t h e burette under examination. I t differs, however, from t h e previous instruments by its using t h e two-way glass cock as a zero adjustment instead of t h e usual mark on t h e lower stem. The enlargement a t C may also be looked on as a n improvement, since i t furnishes a convenient place for attaching t h e clamp for holding i t a n d also permits t h e use of a rubber stopper for connecting t o t h e burette, which makes a more satisfactory joint t h a n t h e g u m tubing t h a t would otherwise h a r e t o be employed. All of t h e previously described pipettes of this sort have had a mark on t h e lower stem which served as a zero point, t o which t h e water was adjusted before a portion was drawn out of t h e burette for measurement a n d a t which t h e outflow was stopped when t h e pipette was emptied t o make room for t h e next portion from t h e burette. T h e accompanying figure will illustrate this form of pipette if a mark around
T H E J O U R N A L OF I-VDL-STRIAL A N D ENGINEERING CHEMISTRY
690
t h e s t e m be imagined at F. T h a t such a m a r k is redundant arid t h a t t h e two-way cock can serve as a self-adjusting zero can be seen b y reference t o t h e figure, in which t h e cock is represented in t h e position of allowing t h e flow of liquid t o t a k e place from t h e b u r e t t e into t h e pipette. It will be seen t h a t , if t h e pipette has previously been filled a n d emptied, t h e flow will begin a t t h e t o p of t h e boring through t h e plug of t h e cock as indicated a t A. Furthermore. since t h e operation of t h e cock is such t h a t t h e connection with t h e burette is closed before t h e outflow through t h e t i p can begin a n d t h e outflow through t h e t i p is closed before t h e inflow from t h e burette c a n begin, i t is evident t h a t , after t h e pipette is emptied a n d another portion of liquid is t o be drawn from t h e burette, its flow will also begin at t h e t o p of t h e boring at A a n d so on for all succeeding portions. This makes t h e point A a zero mark t o which t h e adjustment of liquid is automatically regulated b y t h e position of t h e cock. Rloreover. this zero point is more accurate t h a n a m a r k around t h e lower s t e m would be on account of t h e smaller diameter of t h e boring. GENERAL
POIXTS IS THE
CSE
O F SUCH CALIBRATISG
PIPETTE
First, there can be no question of t h e accuracy of t h e method. Owing t o t h e smaller bore of t h e s t e m of t h e pipette t h e readings are t e n times more delicate t h a n on t h e burette. I n other words, differences of 0.001cc. can be noted in t h e pipette as readily as 0.01 cc. in t h e burette. An error might possibly be introduced b y carelessly allowing a considerable difference in temperature t o occur between t h e water as measured in t h e burette a n d i n t h e pipette. Ordinary care will. however, prevent such differences so t h a t it is safe t o assume t h e temperature of t h e water t o be t h e same -within t h e limits required b y t h e nature of t h e work. A similar assumption is made b y t h e Bureau of S t a n d ards in its method of calibrating flasks b y delivering into t h e m measured volumes of water from s t a n d a r d pipettes .' Secondly, there can be no question of t h e t i m e saved b y t h e use of these calibrating devices because adjusting t h e meniscus i n t h e pipette when drawing off a portion of water from t h e burette is a brief operation compared with making a weighing, a n d finally because there are no temperature corrections t o calculate. T h e pipette when once calibrated for t h e s t a n d a r d temperat u r e (zoo) for glass apparatus, m a y be assumed t o 1
Osborri and Veazey, Bullelin B. of S.. 4 (1908), 589.
1'01. 7, KO.8
retain a constant volume so far as ordinary laboratory temperature changes are concerned. T H E CALIBRATIOK O F T H E PIPETTE
It is evident t h a t t h e capacity of t h e calibrating instrument itself must be determined with great care a n d t h a t this must be done b y weighing t h e water required t o fill i t . F r o m this weight a n d t h e temperat u r e of t h e water its 77olume can be calculated. T h e methods for making such calculations are t o be found in a n y large text-book on quantitative analysis and, therefore, will not be repeated here. In this connection see also t h e Bulletin of t h e Bureau of Standards cited above. At t h e outset, however, an i m p o r t a n t point in t h e calibration of such pipettes should be noted: t h e usual rapid r a t e of outflow of t h e ordinary burette must be restricted or t h e results will be in error. This is because in calibrating t h e burette, successive, small portions (pipettefuls) are drawn off with a n interval of time between t h e readings while in a n actual t i t r a tion 30 t o 4 0 cc. m a y be drawn off a t once. T h e former method gives more water because, being t h e slower, there will be more drainage.' T h e difference due t o variable drainage m a y amount t o as much as 0.1cc. in t h e lower p a r t of t h e scale in burettes as ordinarily received from t h e manufacturers. If, however, t h e r a t e of outflow be sufficiently restricted (see footnote below) this difference in drainage between emptying t h e greater p a r t of t h e burette in a series of small portions or all in one portion, becomes negligible. I n earlier articles this point has received no mention, though t h e method of Morse a n d Blalock eliminates t h e error. These authors, however. do not discuss or even allude t o this advantage of their plan. T h e same situation exists in t h e case of calibrating a burette b y weighing. If successive small portions are drawn off in t a n d e m t h e results obtained for t h e lower p a r t of t h e burette will difier from those obtained b y starting a t zero, unless t h e r a t e of outflow is small. T h e Bureau of Standards, though recognizing t h e small size of t h e error occasioned b y t h e t a n d e m method of calibrating burettes \vi t h restrict e d out 1et s neve r t he1ess f 011o iv s t h e more accurate plan of starting a t zero each time when drawing off t h e portion of water t o be weighed. Similarly, t h e a u t h o r prefers t h e Morse-Blalock method for getting t h e capacity of t h e calibrating pipette. It has t h e merit of eliminating a n y possible tandem-error a n d a t t h e same time is, if anything, a trifle shorter t h a n other methods. Ahwill be seen below! i t does not give t h e t r u e capacity of t h e pipette b u t rather t h e capacity corrected for a n y difference in drainage between emptying t h e burette in successive, small portions t a k e n o u t in t a n d e m , as compared with drawing o u t t h e same a m o u n t of water in one portion; for example, o t o j cc., j t o I O cc., etc., t o 3j t o j o cc. as compared with o t o j o cc. in one portion. illorse a n d Blalock's procedure is t o determine t h e capacity of t h e pipette i n an ifldirect way, b y dividing t h e volume of water delivered directly from zero t o a mark near t h e b o t t o m of t h e burette scale, b y t h e 1
Schloesser, 2. anal. Chem., 46 (1907), 392.
Aug., 191j
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 E SG1;L‘EE RI.VG C H E M I S T R Y
number of pipettefuls t h a t can be drawn off t o t h a t mark. For example, with a pipette like t h e one shown here, t h e capacity of which is about j cc., it is evident t h a t with a 50 cc. burette, I O pipettefuls can be obtained if t h e capacity is less t h a n 5 cc., or 9 pipettefuls if t h e capacity is a little more t h a n j cc. Assuming t h e l a t t e r , let t h e reading of t h e burette be 45.23 cc. when t h e n i n t h pipetteful has been reached. T o get t h e corrected capacity of t h e pipette, t h e burette is again filled t o zero a n d t h e water allowed t o flow out i n t o a small flask t o 45.23 cc. on t h e scale. This water is weighed, its temperature taken a n d its volume calculated. One-ninth of this is t h e n t h e volume of t h e pipette t o be used in calibrating burettes. It is not t h e t r u e capacity of t h e pipette because t h e amount of water obtained b y allowing t h e burette t o e m p t y itself at its normal r a t e from o t o 43.23 is slightly less t h a n t h e a m o u n t t h a t would be gotten b y drawling i t o u t in nine portions with a considerable interval of time between each portion. METHOD O F MARKING T H E P I P E T T E
T h e author of course hopes t h a t n o one will continue t o p u t a m a r k on t h e lower s t e m of such calibrating pipettes, b u t there still remains t h e marking of t h e upper stem. This can be done as follows: (I) A single mark arbitrarily placed is p u t around t h e upper stem. T h e exact capacity of t h e pipette from t h e stopcock t o this mark is t h e n determined b y t h e method of Morse a n d Blalock. Such a n ins t r u m e n t will measure successive portions of t h e same volume a s t h e y are drawn from t h e burette a n d t h e successive burette readings will correspond t o t h e multiples of t h e capacity of t h e pipette. A variation of this plan consists in locating t h e m a r k on t h e upper s t e m so t h a t it will correspond t o some convenient whole number of cubic centimeters, such as 2 cc. or 5 cc. This is no advantage because, in a n y event, t h e burette readings will not fall on t h e marks of t h e burette representing such integral numbers or their multiples, a n d for plotting a correction curve t h e readings obtained b y using a n arbitrarily marked pipette would be of equal value with those obtained by t h e second met,hod. (2) A scale divided arbitrarily into small units approximating 0.01cc. or so t h a t each division corresponds exactly t o 0.01cc. may be combined with a major capacity mark which m a y be located in either of t h e ways described in ( I ) above. I n using a pipette equipped with a scale, successive portions of t h e same nominal value, such as from o t o j cc. on t h e burette, j t o I O cc. or whatever value t h e capacity of t h e pipette m a y be, are drawn o u t a n d their exact volume determined b y measurement in t h e pipette. “This appears t o be a n advantage, which is, however, more apparent t h a n real, a n d will hardly p a y for t h e extra labor required for t h e construction a n d location of such a scale unless a very large number of burettes are t o be tested. I n either case a correction curve can be made a n d t h e values corresponding t o integral marks on t h e burette ( I , 2 , 3 cc., etc.) can be calculated upon t h e reasonable assumption t h a t t h e bore of t h e burette does not change appreciably in a short
691
length. Therefore, t h e error a t a n y integral mark will be t h e same as a t a n y reading in t h e immediate vicinity. Thus, if a t 14.71 cc. t h e error is 0.05 cc., t h e same correction may be applied a t I j cc.” It might be interesting t o compare t h e above method with t h e more laborious one employed in one of t h e previous articles on burette calibrating pipettes. T h e exact volume corresponding t o t h e 50.00 cc. mark on a burette scale had been found t o be j o . n j 8 cc. a n d i t was desired t o find t h e volume corresponding t o 49. 5 2 cc. on t h e same scale. It was done b y solving t h e proportion j O : 50.258 :: 49.52 : x, by which x is found t o be 49.775j CC. ( T h e figures are given as t h e y are f o u n d in t h e article in question.) If instead of making this calculation, it h a d been assumed t h a t t h e error of t h e burette a t 49.52 cc. was t h e same as a t t h e near-by point, 50 cc.-namely, +o.z58 cc.t h e t r u e value of t h e scale reading 49.52 could have been found b y simply adding t h e correction 0.258. This gives 49.7780 cc. which differs from t h e other value, 49.7755 cc. so laboriously obtained, b y only 0 . 0 0 2 5 cc., a n amount which under t h e circumstances could introduce n o error. I n order t o show t h e necessary details in manipulation a n d calculation there will now be given t h e complete procedure for determining t h e capacity of t h e calibrating pipette a n d for using t h e pipette in finding t h e errors of a burette. DETERMIXATIOK
OF
THE
CAPACITY
OF
THE
PIPETTE^
T h e pipette a n d a burette, connected as shown in t h e drawing, are filled with distilled water. Both instruments can be supported on one ring-stand by t h e use of t w o clamps. Air bubbles in t h e connecting parts can be avoided by having t h e enlargement a t C full of water before t h e stopper is inserted. This causes a n overflow through t h e hole, a n d if now t h e tip of t h e burette is also filled before i t is p u t into t h e stopper, no air will be entrapped. T h e level of liquid in t h e burette is adjusted t o zero a n d t h e pipette (which must be full) is allowed t o e m p t y itself through t h e tip a t E. This point of filling a n d emptying before a n actual measurement is made is necessary because t h e capacity of t h e pipette is affected by t h e a m o u n t of liquid on t h e interior. This amount must obviously be t h e same for t h e first pipetteful as for t h e subsequent ones. I n t h e manipulation of t h e stopcocks it will be found convenient t o leave the burette cock open a n d control t h e flow of water entirely with t h e two-way cock of t h e pipette. 1 Before beginning a n actual calibration, t h e r a t e of outflow of both the pipette a n d t h e burette should be adjusted once for all b y properly constricting t h e outlet orifice. T h e stopcocks can t h e n be opened to their full extent a n d t h e r a t e of dow will be correct without further regulation. Specifications from t h e Bureau of S t a n d a r d s require t h e outflow of a burette with a scale 50 cm. long-about t h a t oi a 5 0 cc. burette-to be not less t h a n 90 seconds nor more t h a n three minutes, and t h e free outflow t i m e of a 5 cc. pipette t o be not less t h a n 15 seconds nor more t h a n one minute. The most convenient way of adjusting t h e orifice to a given r a t e of delivery is t o draw o u t t h e tip in a flame so t h a t i t is smaller t h a n desired. One can then gradually enlarge i t b y filing or grinding across t h e end. B y t h i s procedure trial can be made from t i m e t o time without the necessity of waiting for hot glass t o cool or for drying t h e wet glass before heating again, a s would be t h e case if the usual method of allowing t h e tip t o contract in a flame were employed. Finally, everything must be thoroughly cleaned with chromic-sulfuric acid mixture a n d rinsed with distilled water before beginning work.
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 ENGI*VEERING C H E M I S T R Y
692
With t h e level of water in t h e burette a t zero a n d t h e pipette emptied, t h e next step is t o allow water t o flow from t h e burette into t h e pipette till t h e mark a t B on t h e upper s t e m is reached. This portion is t h e n allowed t o flow out through t h e tip a t E . I n this way successive pipettefuls are drawn off a n d wasted through E till a point is reached on t h e burette beyond which another portion would bring t h e level of t h e water below t h e scale. This last burette reading must be carefully noted a n d . though it is t h e only one necess a r y for t h e calibration of t h e pipette, t h e intermediate ones should also be made a n d recorded because t h e y may subsequently be used in determining t h e errors of t h e burette a n d because i t is t h e simplest 1%-ayof insuring t h e same conditions in t h e Calibration as in t h e subsequent use of t h e pipette T h e next step is t o find t h e volume corresponding t o t h e last reading on t h e burette as obtained above. This is done b y disconnecting t h e pipette, filling t h e burette with water, adjusting the meniscus t o zero a n d t h e n allowing t h e water t o flow out a t its normal r a t e into a t a r e d flask till t h e point corresponding t o t h e last pipetteful is reached. This portion of water is then weighed t o t h e nearest milligram a n d from its weight a n d its temperature its t r u e volume in cubic centimeters is calculated. The above experiments should of course be repeated several times till closely agreeing results are obtained, t h e averages of which are t h e n used for t h e final calculations as follows: Suppose t h a t t h e capacity of t h e pipette is such t h a t t h e t e n t h portion drawn from t h e burette b y its use brings t h e level of liquid t o 49.82 cc. on t h e burette scale a n d t h a t t h e weighing of t h e water delivered directly from zero t o this point gave its t r u e volume as 49.88 cc. Since this volume corresponds t o t e n pipettefuls, i t is evident t h a t t h e capacity t o be assigned t o t h e pipette is 4.988 cc. CALIBRATION O F A B U R E T T E
T h e calibration of a burette is carried out by connecting t h e pipette as described above a n d drawing off successive pipettefuls, noting t h e reading each time on t h e burette scale. Assuming a pipette with a capacity of 4.988 cc. a n d a n average burette, readings would be obtained a b o u t a s given in t h e first column of t h e table below. The second column gives t h e t r u e T A B L EI 1
2
3
4
5
Burette readings
Correct volume
Corrections
Burette reading
Correct volume
5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00
4.94 9.94 14.92 19.87 24.88 29.90 34.86 39.86 44.84
5.05 4.99 -0.06 10.04 9.98 -0.06 15.04 14.96 -0.08 20.08 19.95 -0.13 25.06 24.94 -0.12 30.03 29.93 -0.10 35.06 34.92 -0.14 40.04 39.90 -0.14 45.05 44.89 -0.16 Correction for 50.00 cc. is found b y SO+
t h e method illustrated in
Table I1
volume corresponding t o t h e readings a n d is obtained b y multiplying t h e capacity of t h e pipette b y t h e serial number of t h e interval measured a n d rounding off t h e numbers t o two decimals. Column 3 gives t h e corrections for t h e points in Column I a n d , since t h e corrections are t h e same for all points in t h e immediate vicinity of a given point, t h e numbers in Column 3
Vol. 7, No. 8
are also t h e corrections for t h e burette readings as given in Column 4. Column j gives t h e volumes corresponding t o t h e “ 5 cc.” points o n t h e scale. T h e above figures are from an actual burette a n d present a complication t h a t may sometimes arise; namely, t h a t when starting a t zero t h e last pipetteful may bring t h e burette reading below t h e scale. This situation is, however, easily remedied by a simple trick of manipulation. Two or three sets of readings are wanted in a n y event in t h e interests of accuracy a n d when t h e first series shows t h a t t h e last pipetteful brings t h e reading below the scale, t h e next series is started a little above t h e beginning of t h e second interval; in this case, for example, a t 5.00 cc. on t h e burette scale. T h e burette readings are t h e n as follovs: I
T A B L EI1
I1
Burette reading Correct volume 5.00 4.94 T h e correct volume corresponding to t h e burette reading of 5.00 cc. is t a k e n from 9.99 9.93 15.00 14.92 Table I 20.03
19.90 24.89 29.88 34.87 39.86 44.84 49.83
25,Ol 29.98 35.01 40 00 45.00 49.98
T h e t r u e volumes corresponding t o t h e readings are obtained b y adding t h e appropriate multiple of t h e capacity of t h e pipette t o t h e volume corresponding t o t h e starting point which is taken from Table I a n d which must be checked b y a separate experiment. This series of readings in Table I1 also gives t h e corrections for points in t h e immediate vicinity of those marks on t h e burette scale which are multiples of j a n d consequently may be applied a t once t o those marks. I n other words, t h e y are check readings on those of Table I , a n d in addition give t h e value of t h e correction for t h e j o cc. mark. If a correction curve is t o be made, t h e above d a t a are sufficient. I n case it is desired t o t a b u l a t e t h e corrections for each “cubic centimeter” mark on t h e scale of t h e burette t h e following procedure should be used: ( I ) The t r u e volume of each j cc. interval of t h e burette is found b y a series of subtractions based on t h e values in Table I , Column j; ( 2 ) t h e value of I cc. in each interval is found b y dividing t h e t r u e volume of t h e i n t e r v a l b y j . Table I11 illustrates these two points. T A B L EI11 Interval on Volume burette scale of interval 0 to 5 4.94 5 t o 10 = ( 9 9 4 4.94) = 5.00 1 0 t o 15 (14.929.94) = 4.98 40 t o 45 = (44.84 - 39.86) = 4.98 45 t o 50 = (49 85
- 44.84)
=
Value of “1 cc.” in interval 0.988 1 ,000 0.996 0.996 1.002
5.01
T h e final tabulation is made b y adding these cubic centimeter values in Table 111,t h e results being rounded off t o t w o decimals. Table I V , below, covering p a r t of t h e burette scale, shows this. Burette
True
4 5
0.99 1.98 2.96 3.95 4.94 5.94 6.94
6
7
T A B L EI\‘ Burette True reading volume 8 7.94 9 10 11 12
.. ..
8.94 9.94 10.94 11.93
..... .....
Burette reading
True volume
44 45 46 47 48 49 50
43.84 44.84 45.84 46.84 47.85 48.85 49.85
If this, plan is used, t h e tabulation should be made
Aug., 191j
T H E J O C R N A L OF I N D C S T R I A L A N D ENGINEERING CHEMISTRY
on a stiff piece of paper or board so t h a t it can be hung up near t h e burette. CONCLUSION
I n this article there has been described a modification of a burette-calibrating pipette t h a t eliminates t h e mark on t h e lower stem and provides for t h e use of a two-way cock as an automatic zero-adjusting de vice . A discussion of the principles underlying t h e calibration and use of such pipettes is also given. DEPARTMENT OF CHEMISTRY, OHIOSTATEUNIVERSITY COLTXBUS,OHIO
AN AD JUSTABLE BURNER SUPPORT FOR CONDENSATION APPARATUS By H. E. BISHOP Received April 19, 1915
The condensation apparatus described by H. E. Barnard a n d H. E. Bishop in t h e Journal of the American Chemical Society, 28 (1906)~999, was designed for use with flasks of uniform size only. The burner and flask supports were so arranged t h a t in changing the adjustment of t h e still i t was necessary t o move them as a unit. T o overcome this difficulty t h e burner a n d flask support t o be described was designed. The condensation tubes, water connection and their supports were not changed. The gas supply was changed from a position under t h e flask support t o t h e top of the supports for t h e condensing tubes A .
693
attached to the gas pipe. This pipe, hanging in a perpendicular position, forms t h e rod for the ring which supports t h e flask. I n t o this tube was fitted a brass tube, C, which would slide easily. T h e lower end of this sliding tube was soldered into a '/a in. brass elbow, E . A 2-in. '/8 in. nipple, N , was screwed into t h e other side of t h e elbow; then a ' / 8 in. coupling, F , which in t u r n took t h e air cock, was attached. Another elbow was attached t o the air cock G which took the nipple for the tube of t h e Bunsen burner H . The gas joint, which allows the burner t o be adjusted up or down, is similar t o the old gas drop-light which was on the market before the use of rubber tubing was so general. The lower end of the tube B , which forms t h e ring support and the outside member of the extension tube, was threaded t o take an ordinary packing box, P , similar to those used a t t h e top and bottom of the condensing tubes. Ordinary candlewick packing, well oiled, was used. The addition of a ring, R , from t h e regular ring stand, completed the apparatus. The,great advantage of t h e apparatus is its wide range of adjustment for individual operations. Flasks from 5 in. t o 14 in. high can be used simultaneously. The sliding gas tube overcomes t h e necessity for rubber connections and if more heat is desired, two burners may be turned under one ring. T h e cost of construction is small and t h e upkeep is ail. INDIANA STATE BOARDO F HEALTH INDIANAPOLIS
A NEW AND IMPROVED FORM OF KJELDAHL DISTILLATION APPARATUS By ARTHURD. HOLMES Received March 9, 1915
A description was given in THISJ O U R N A L , 6 (1914), of a Kjeldahl apparatus which has given satisfactory service in this laboratory. This apparatus as described, when set u p on a laboratory table of t h e usual height, has been found somewhat too high for convenience when used b y a person of short stature. T o avoid this difficulty, t h e apparatus may be modified as indicated in t h e accompanying sketch, which should be substituted for Fig. I1 of the original article. The height may be decreased 6 t o 8 in. by replacing t h e upright type of burner with a horizontal offset burner, and shortening t h e condenser pipe accordingly. It is well t o make sure, however, t h a t the diameter of this pipe, and t h e rate of flow of the water in it, are sufficient t o insure condensation in the tube H . The modification not only lessens height, but also obviates t h e disagreeable results which often follow IOIO,
T h e gas pipe was already tapped for ' / 8 in. air cocks t o which the burners were attached. The air cocks were replaced by in. close nipples. An 1 1 in. length of 9 / l e in. (outside diam.) brass pipe, B , was tapped a t one end t o fit the '/a in. close nipple and
