Feb., 1916
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
precipitate tended t o clog t h e spiral t u b e with t h e result t h a t occasionally gas would escape from t h e opening at t h e bottom of t h e spiral a n d bubble u p through t h e reagent. Also, on returning t h e gas t o t h e burette for measurement, i t was found frequently t h a t gas would be retained in t h e spiral a n d liberated some little time after t h e volume of t h e sample had been read. This objection became more a n d more serious, until finally t h e reagent was discarded before i t h a d become exhausted. The accumulation of precipitate in t h e Dennis pipette gradually increased t h e resistance offered t o t h e passage of gas until, in some cases, a portion of t h e sample was forced into the leveling a r m of t h e pipette when only two minutes were allowed for t h e complete transfer of t h e sample t o the pipette. I n t h e case of t h e pipette from which the d a t a in t h e table were obtained, i t was possible, by careful manipulation, t o exhaust t h e reagent t o t h e point where it would no longer absorb oxygen completely in a reasonable length of time without much trouble from this source. I n t h e Orsat pipette, t h e precipitate clogged t h e lower ends of t h e outer glass tubes with t h e result t h a t , as t h e precipitate increased in amount, it became more a n d more difficult t o introduce a sample of gas into t h e pipette without loss of gas into t h e leveling a r m of t h e pipette. Also, at about t h e time when absorption failed t o be complete with one-minute contact, small bubbles of gas were frequently retained in t h e pipette as t h e gas was withdrawn. For these reasons, no attempt was made t o determine t h e specific absorptions for longer contact of t h e gas with t h e reagent. The formation of a precipitate which appears to contain t h e various oxidation products of alkaline pyrogallol1 is t h e cause of practically all of t h e difficulties of manipulation of the modified reagent in t h e pipettes t h a t have been employed. I n a n effort t o further modify t h e reagent so t h a t this objection might be removed without too great a sacrifice of specific absorption, experiments were performed to ascertain t h e effect on t h e formation of precipitate of variations in t h e amounts of pyrogallol and potassium hydroxide. The effect of varying t h e amount of pyrogallol was first determined. It was known from previous work2 on alkaline pyrogallol t h a t , within certain limits, a decrease in t h e amount of pyrogallol would cause a nearly proportional decrease in t h e specific absorption of the reagent, but i t seemed possible t h a t a reduction in t h e amount of pyrogallol might prevent t h e formation of precipitate a n d thus result in a more satisfactory reagent. Accordingly solutions were prepared which contained l/3 a n d 2/q of t h e usual amount of pyrogallol and these were exhausted as previously described. It was found t h a t there was no apparent advantage in using less pyrogallol, t h e amount of precipitate being, as far as t h e eye could judge, proportional t o the amount of oxygen which 2
See Berthelot, Ann chim. p h y s . . [7] 16 (1898), 294. Loc c i f .
I33
t h e reagent h a d absorbed a n d independent of t h e amount of pyrogallol employed. The relation of t h e amount of alkali t o t h e formation of precipitate a n d t o t h e specific absorption of t h e reagent was next considered. It seemed probable t h a t t h e formation of a precipitate in alkaline pyrogallol could be retarded or prevented by using less potassium hydroxide in t h e preparation of the reagent. Such a procedure would probably lessen the specific absorption of the reagent. To obtain information on these points, solutions were prepared using alkali of specific gravity I . 50 and 1.45. These solutions were exhausted in t h e usual manner, first in t h e Hempel pipette for use with mercury and then in t h e Orsat and Dennis pipettes. The results of t h e determination of specific absorption are shown in Table 11, data on the original solution being included for p y p o s e s of comparison. TABLE11-SPECIFICABSORPTION OF ALKALINEPYROGALLOL IN HENPELPIPETTE ORYAT PIPETTE DENNISPIPETTE ' FOR FOR FOR 7 #-on-. .Specific gravity I-min. of alkali shakina 27 1.55 5 1 . 5 0 ...... 0 1.45
...... ......
2-min. shakiria 30 24 6
tncts 1-min. 1 min. contact each 22 .. 1% 29 0 24
2 passages 2-min. 1st-2min. Dassaze 2nd-1 min. 7 28 3 24 0 9 -
I
The reagent prepared from alkali of 1.45 specific gravity showed much less precipitate t h a n the others, but t h e specific absorption of this reagent is much too low for general use. Considerable precipitate was formed in the reagent prepared from alkali of I 50 specific gravity and this caused a certain amount of inconvenience of manipulation, much less, however, t h a n follows from t h e use of the original solution The drop in specific absorption t h a t accompanies the use of alkali of r . jo rather than I . 5 5 specific gravity is quite pronounced except when t h e DenniJ pipette is employed. Of t h e two reagents, it appears t h a t t h e one containing the smaller amount of a l k d i is better mited for use in this pipette, since the gain in convenience of manipulation seems to more than offset the small loss in specific absorption. From t h e results of t h e experiments t h a t have been described, i t may be said t h a t t h e modified alkaline pyrogallol is not well suited for use in pipettes t h a t have been designed for the absorption of oxygen without shaking, nor can it apparently be readily adapted for convenient use in these pipettes without considerable loss in specific absorption. It seems feasible, however, t o adapt the pipettes t o t h e modified reagent, and a modification of the Orsat pipette in which t h e accumulation of precipitate does not interfere appreciably with its manipulation is described in t h e following article. C0RNEI.L UNIVERSITY, ITHACA. N E W Y O R K
PIPETTES ESPECIALLY ADAPTED FOR USE WITH ALKALINE PYROGALLOL By R. P. ANDERSON Re,rived August 30, 1915
It has been shown in t h e foregoing article t h a t t h e Orsat pipette is probably superior for t h e absorption of oxygen by alkaline pyrogallol t o any of t h e pipettes t h a t have been suggested as a substitute for i t in t h e
T H E J O C R N A L O F I N D r S T R I A L A-VD E Y G I N E E R I S G C H E M I S T R Y
I34
Orsat apparatus, provided certain proportions of pyrogallol and potassium hydroxide are employed in t h e preparation of t h e reagent. T h e inconveniences a t t e n d a n t upon its use are inconveniences of manipulation, due t o t h e formation of a precipitate, which i t was n o t . found possible t o eliminate b y changing t h e composition of t h e reagent without undue loss in specific absorption. I n t h e form of Orsat pipette shown in Fig. I , t h e accumulation of precipitate is not a serious objection t o its use. T h e construction of t h e upper end of t h e pipette is such t h a t very little precipitate clings t o it and no trouble is found from t h e retention of gas a t this point, as is the case with t h e usual form of t h e Orsat pipette. The perforated porcelain cone forms a support for the glass tubes and has t h e advantage over t h e horizontal perforated plate sometimes employed t h a t the precipitate cannot collect and clog t h e lower ends of the glass tubes. Gas can be passed rapidly into this pipette, even when considerable precipitate has accumulated, 11-ithout danger of its being forced into the leveling a r m . The length of .the cylindrical portion of t h e left-hand t u b e is 13 cm. and its diameter, 3 . 6 cm. Thin-walled glass tubes about j mm. in diameter are employed t o increase t h e surface of the reagent in contact with a gas sample a n d 2 7 of these are required t o fill t h e pipette. On account of the differences in manipulation of t h e pipette in question and t h e Hempel pipette. t h e proportions of pyrogallol and potassium hydroxide t h a t were recommended as t h e result of previous work' for t h e preparation of alkaline pyrogallol for use in the latter pipette. are not necessarily the most desirable for use in the former. An increase in t h e amount of pyrogallol in t h e solution results in a reagent t h a t foams appreciably on shaking, b u t since t h e manipulation of t h e proposed Orsat pipette does not involve shaking, i t would seem t h a t higher concentrations of pyrogallol might be employed, t h u s resulting in a n increase in specific absorption. T o test t h e t r u t h of this assumption, the specific absorption of each of a series of solutions of alkaline pyrogallol was determined using t h e modified Orsat pipette. T h e solutions were prepared by dissolving a definite amount of pyrogallol in 2 0 0 cc. of a solution of potassium hydroxide of specific gravity I . j j , t h e one obtained by using 30 grams of pyrogallol being t h e solution suggested for use in t h e Hempel pipettes where t h e gas sample is shaken with t h e reagent. The values of specific absorption were obtained at room temperature (20- 24' C , ) , for samples of gas I O O cc. in volume containing 2 0 . 9 per cent oxygen, and for one-minute contact of gas and reagent. T h e results follow: Grams pyrogallol t o 100 cc. alkali. Specific absorption of the solution.
,, ,
. , . 15 . , , , , . , . 25 .O
20 31.2
25 36.1
30 37.8
T h e saturation of each reagent was stopped a t the point where there was a noticeable retention of gas between t h e glass tubes in t h e pipette due t o t h e clogging of some of t h e smaller openings b y precipitate, and t h e values of t h e specific absorption given in 1
THISJOURNAL, 7 (1915), 587.
Trol 8 , No.
2
t h e table were obtained from the volume of gas absorbed u p t o t h a t point. This retention of gas seems to. occur a t or slightly before t h e time when absorption fails t o be complete for one-minute contact of gas with t h e reagent. The increase in specific absorption t h a t results from t h e increased concentration of pyrogallol is pronounced' up t o a concentration of 2 ; grams of pyrogallol, and since there is b u t little advantage in using still more pyrogallol, t h e solution containing 2 5 g. of this constituent was chosen as being t h e most desirable for use in this pipette. Dissolving z j grams of pyrogallol in I O O cc. of a solution of potassium hydroxide of I . j j specific gravity results in a volume of about 118 cc. a n d there are t h u s 2 1 . 2 grams of pyrogallol and 6 6 . 6 grams of potassium hydroxide t o I O O cc. of t h e proposed reagent. F r o m a comparison of t h e specific absorption ob-
M
FIG.I
FIG I1
tained in this modified Orsat pipette using t h e above reagent with that2 obtained in the Hempel double pipette using the reagent best adapted t o i t , it appears t h a t there is considerable advantage in using the former pipette; further, t h e fact t h a t no shaking is required emphasizes t h e superiority of the proposed pipette; therefore, it seems desirable t o a d a p t this modification of t h e Orsat pipette for use in a frame such as ordinarily is employed t o hold a Hempel double pipette for solid and liquid reagents. The form t h a t is suggested is shown in Fig. 11. It differs from t h e usual Hempel double pipette, for solid reagents in having a smaller cylindrical bulb and a much more gradual constriction a t its top. It was found t h a t t h e cylindrical portion of the usual Hempel double pipette of this form is much larger t h a n necessary when thin-walled glass tubes are used as contact material and in this connection it is desirable to have a s small a bulb as possible in order t o decrease t h e volume of t h e space between t h e upper ends of t h e tubes and the t o p of t h e bulb. T h e cylindrical portion of t h e bulb is 7 cm. and its diameter j cm. T h e construction of t h e glass part at the bottom of the bulb is such t h a t t h e glass tubes are held in position 1 2
LOG.c i l . See particularly Curve 11 in Fig. 4. Lac. cil. 25 for one-minute shaking.
Feb. , I 91 6
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 C H E M I S T R Y
and at t h e same time they can not readily become clogged with precipitate. This form has the advantage over t h a t in Fig. I t h a t t h e glass tubes are removable. If i t is desired t o eliminate t h e rubber stopper a t t h e base of t h e pipette, t h e construction of t h e lower end of t h e cylindrical bulb can be made identical with t h a t in Fig. I. An opening' (not shown in t h e figure) between t h e first and last two bulbs which is closed b y a small cork or rubber stopper is a great convenience in filling a n d cleaning t h e pipette. The specific absorption t h a t may be obtained in this pipette' is practically t h e same as t h a t obtainable with t h e pipette shown in Fig. I, aiz., 3 6 . I for t h e reagent prepared as suggested and exhausted under conditions t h a t are there specified. I t was found t h a t t h e pipettes t h a t have been described are not well adapted t o t h e analysis of samples of nearly pure oxygen12a n d for this reason no determinations of specific absorption for gas samples containing 90 per cent oxygen, such as have been published for t h e Hempel pipettes, were made. When a gas sample high in oxygen is placed in contact with t h e reagent in either of these pipettes in t h e usual manner, rapid absorption occurs up t o what apparently corresponds t o the exhaustion of t h e film of reagent upon t h e glass tubes and t h e inner wall of t h e pipette; thereafter absorption is slow unless t h e remaining gas is passed into t h e burette and returned in order t o moisten t h e contact material with fresh reagent. Even with this latter procedure, considerable time is consumed in effecting complete absorption, partly because of the intermittent contact of gas and reagent, and partly because of t h e decrease in t h e amount of contact material in proportion t o t h e size of t h e gas sample as the latter becomes small a n d occupies only t h e upper portion of t h e pipette above most of t h e glass tubes. Therefore, it is believed t h a t when t h e analysis of gases high in oxygen is frequently made, t h e Hempel pipette should be employed. On t h e other hand, when such samples are met with infrequently, as is usually t h e case, t h e longer time required for their analysis will not prove a great objection, especially if the pipette is shaken t o hasten t h e absorption when t h e volume of t h e sample has become too small t o uncover t h e tops of the glass tubes. SUMMARY
I-Pipettes especially adapted for use with alkaline pyrogallol are shown in Figs. I and IT. These pipettes are constructed in such fashion t h a t t h e formation of precipitate, a characteristic of alkaline pyrogallol of high specific absorption, is not objectionable until t h e reagent has nearly become exhausted. 11-It has been found possible t o employ a reagent containing a higher concentration of pyrogallol t h a n t h a t recommended for use in t h e Hempel pipettes. This reagent is prepared b y dissolving 2 j grams of pyro1 This construction is shown on a special pipette for use with cuprous chloride, designed by the United Gas Improvement Co., in the catalogs of Eimer & Amend a n d A. H. Thomas Co. 2 This appears to hold true for all pipettes in which the gas sample is not shaken with the reagent.
I35
gallol in I O O cc. of a solution of potassium hydroxide of I . j j specific gravity, which results in a volume of about 118 cc. There are thus 2 1 . z grams of pyrogallol a n d 6 6 . 6 grams of potassium hydroxide t o I O O cc. of t h e solution. 111-The specific absorption of t h e above reagent for I-minute contact is about 36 when treated in t h e proposed pipettes at room temperature (20'-24' C.) with gas samples I O O cc. in volume containing 2 0 . 9 per cent oxygen. This is a decided gain both in specific absorption a n d convenience of manipulation over t h e results t h a t have previously been obtained with t h e Hempel pipette (specific absorption z j , for I-minute shaking). No determinations of specific absorption for samples of nearly pure oxygen were made, since complete absorption can not be obtained in these pipettes in less t h a n 4 or 5 minutes unless shaking is employed t o facilitate t h e removal of last traces of oxygen. C O R L E L L U N I V E R S I T Y , ITHACA,
NEW
YORK
REAGENTS FOR USE IN GAS ANALYSIS IV-PHOSPHORUS IN SOLUTION By R. P. ANDERSONA N D W. BIEDERMAN Received September 3, 1915
Centnerszwerl has proposed t h a t a solution of phosphorus be employed t o r.eplace solid phosphorus as a n absorbent for oxygen in gas-analytical work, since the behavior of t h e latter reagent is appreciably influenced by temperature, percentage of oxygen in t h e mixture, a n d t h e presence of certain other gases. Castor oil was chosen as t h e solvent for phosphorus because i t possesses a negligible vapor pressure a t ordinary temperatures and because i t dissolves t h e products of t h e oxidation of the solute. It was thought desirable t o study further t h e solution which Centnerszwer recommends, with t h e idea of determining how long a time is required for t h e complete absorption of oxygen under ordinary conditions a n d what specific absorption may thus be obtained. Accordingly, solutions of phosphorus in castor oil were prepared by t h e method which he employed, which is as follows: About 230 cc. of castor oil a n d 3 grams of well-dried phosphorus are placed in a flask of 2jo cc. capacity, a well-fitting stopper is loosely placed in t h e neck of the flask, and its contents heated in a n oil bath t o zoo'. The flask is then removed from t h e bath and dried with filter paper, and, after tighty inserting t h e stopper, i t is wrapped in a towel and vigorously shaken t o effect complete solution of t h e phosphorus. When cool, the solution is transferred t o a pipette and is then ready for use. T h e precaution of wrapping t h e hot flask with a towel before shaking, as specified by Centnerszwer, is a n important one as regards t h e safety of t h e operator, since considerable pressure is developed when t h e shaking is started, especially if t h e castor oil does not almost entirely fill t h e flask, and in one instance t h e flask was shattered by t h e pressure produced. Samples of air were brought into contact with t h e reagerit a t z j ' C. in Hempel pipettes for solid and liquid 1
Chem. Ztg.. 5 4 (1910). 494.
