An Evaporation Rate Method Applied to Petroleum Thinners D. D. RUBEKAND G. W. DAHL,Anderson Prichard Oil Corp., Oklahoma City, Okla.
T
HE method in most general use for expressing the evaporation curve was obtained. A method which gives a volatilities of solvents and thinners is graphical (4, 6, straight-line evaporation curve for c. P. compounds should 7, 9 ) , plotting per cent liquid remaining, or per cent give a true representation of the evaporation curve of a evaporated, against time elapsed. No satisfactory sub- petroleum thinner. stitute for graphical representation of the volatility of heteroDEVELOPMENT OF METHOD.The use of a dished container geneous liquids such as naphthas and the less pure grades overcame the difficulty of the uneven wetting of the bottom of a of solvents has been devised or proposed, as no other method pan with a flat inner surface, but caused a change in the evaporasurface area of the liauid and a subseauent elongation of the shows the change in volatility as the liquid evaporates. Most tion evaporation curve as drfness was approached. It-is desirable of the work in this field has been towards refining the pro- to have the surface constant to the end of the evaporation, since these data are t o be used in studying the behavior of cedure for obtaining these "loss in weight-time the liquids in films from which they evaporate from a elapsed'' curves (1,3,4, 6,8). TRIPOD constant surface. Perhaps the most popular vessel used today in It was found that the objection t o the use of a flatT,LILR running evaporation curves is a small metal pan, m bottomed pan was made less by putting into the pan often simply the lid from a friction-top can (4). a piece of high-grade filter paper, cut to fit into the rRImoN'ToP(RNL'D bottom of the pan with its edges just barely touchIn order to lessen errors due to stray air currents ing ~ the ~ sides. Theoretically, a pure s u b Wilson and Worster (IO) suggested that during F~~~~~1. A ~ stance should give a straight-line curve, provided the RATUS evaporation the pans be kept in a small wooden evaporating surface remains constant, since in such tunnel. The Hart balance (6) avoids the troublea liquid no physical characteristic will change during some manipulation of the analytical balance. Ivanovszky (8) the course of evaporation. Eva oration curves of c. P. benzene c. P. toluene run by this metgod, although greatly improved, describes a recording balance for drawing evaporation curves. and still showed a slight variation from the straight-line evaporation In order to avoid variations in data due to cooling of the desired, apparently caused b a bellying or lifting of the filter liquid by evaporation and the effect of stray air currents, some paper from the bottom of t l e pan as dryness was approached. laboratories suspend the evaporation vessel from a Jolly bal- This was overcome by placing in each pan a small wire-legged tripod (total weight approximately 10 grams). Evaporation ance (4)?supported in a celluloid chimney. curves, run from pans containing filter paper and tripod weights, The friction-top can lids, a t present widely used, have one on c. P. benzene and c. P. toluene showed that these comDounds limitation in common with the Petri dish method (4). The evaporate in a straight line. flat bottom is unevenly wetted towards the end of the evaporation, causing a decrease in size of the evaporating surface. This gives an undue flattening of the curve towards the end of the evaporation and a false final dry time. Bridgeman ( I ) proposes to eliminate this uneven wetting by using pans with a slightly dished bottom, so that equal volume of liquids will have equal evaporating surfaces. By a method developed in this laboratory a constant evaporation surface was apparently maintained, and the evaporation was allowed to proceed under conditions closely duplicating actual use of solvent in industry. When C. P. material was evaporated by this method, a straight-line z
-
i
x*
TIME IN MINUTIS
FIGURE3. EVAPORATION CURVE
FIGURE2. EVAPORATION CURVE
APPARATUSAND PROCEDURE. The pans used in these testa were ordinary friction-top can lids (Figure l), measuring about 6.5 cm. in diameter (inside) and 0.75 cm. in depth. Munktell's Swedish filter paper No. 0 was used. The tripod weights were simple affairs, merely three wire legs and a small weight at the apex, and were built low enough so that they were not easily tipped over, those used in these tests being 3 cm. high. The wire legs were made so that the tripod rested on the edge of the filter paper in the pan, with lower ends rounded BO as not t o pierce the filter paper. In these 3 cc. of liquid were used, this being a convenient volume for the size of the pan. 421
422
ANALYTICAL EDITION
Vol. 6, No. 6
rate curves is less than might be expected from experimental error. These charts indicate, therefore, that the difference in evaporation rate between Petrobenzol and c. P. benzene remained constant under the conditions of the experiment. LITERATURE CITED (1) Bridgeman, J. A., IND. ENQ.CHEM.,20, 184-7 (1928).
FIGURE 4. RATIOCHARTOF EVAPORATION RATES The sensitiveness of this method necessitates precautions to eliminate drafts. I t was found that the air disturbance caused by the opening of a door, or walking rapidly past the pans during the evaporation test was sufficient in some cases to affect the results. This error would cause a variation from the straightline evaporation of a c. P. material.
EXPERIMENTAL. Petrobenzol (a petroleum naphtha which evaporates in about the same time as c. P. benzene) and c. P. benzene were evaporated under varying air conditions: temperatures of 90" F. (32' C.), 75" F. (24' C.), and 65' F. (18' C.), and relative humidities of 20, 45, and 60 per cent. Maximum temperature variation during the test was 2 O F., and maximum relative humidity variation was 1.5 per cent. It was desired t o determine whether c. P. benzene would evaporate in a straight-line curve under less ordinary conditions, and whether the difference of evaporation rate of the two solvents was constant as the air conditions were varied. From data gathered, Figures 2 and 3 were plotted.
DISCUSSION OF RESULTS Figures 2 and 3 show t h a t by this method c. P. benzene gives a straight-line evaporation curve under the air conditions tried. According t o a method previously used (2) for comparing rates of evaporation, the difference in evaporation rate between Petrobenzol and c. P. benzene apparently remained constant under the conditions tried. Figures 4 and 5 , de-
z
RATES FIGURE 5 . RATIOCHARTOF EVAPORATION rived from Figures 2 and 3, show the ratio of evaporation rates of Petrobenzol as compared to c. P. benzene. c. P. benzene, evaporating at a constant rate, was taken as a base line, points above and below the base line representing evaporation rates more and less rapid, respectively, than the benzene. The variation in the Petrobenzol evaporation
(2) Commercial Solvents Corporation, private communication. (3) DeHeen, J. chim. phgs., 11, 205 (1913). (4) Gardner, H. A., "Physioal and Chemical Examination of Paints, Varnishes, Lacquers and Colors," 6th ed., pp. 695708, Institute of Paint and Varnish Research, Washington, 1933. (5) Gardner, H. A., Holdt, P. C., and Bielouss, E., Paint Mfrs.' Assoc. U. S., Circ. 141, 108-23 (Dec., 1921). (6) Hart, L. P., Am. Paint Varnish Mfrs'. Assoc., Circ. 360, 173-9 (Feb., 1930). (7) Hoffman, H. E., IND.ENG.CHEM.,24, 135-40 (1932). (8) Ivanovszky, Leo, Farbe u. Lack, 1932, 231-2, 244-5. (9) Polchich, G., and Fritz, H., Brennstpf-Chem., 5 , 371-3 (1924). (IO) Wilson and W-orster, IND. ENG.CHEM., 21, 592 (1929). RECEIVED May 15, 1934. Presented before the Midwest Regional Meeting, American Chemical Society, Kanaas City, Mo., May, 1934.
Acidity Titration of Low-Grade Rosins During the years 1918 and 1920 there appeared in different well-known journals three communications from this laboratory fully describing a method by which the acidity (or alkalinity) of dark-colored solutions (or clear solutions viewed in artificial light) could be determined with the aid of a "pocket" spectroscope. The conditions of success were laid down for a number of different indicators and considerable detail for phenolphthalein. The method received a t the time more publicity than the authors anticipated. Its general applicability having been shown, it was ado ted here as routine procedure when necessary. TRere has now appeared [IND. ENG.CHEM.,Anal. Ed., 6 , 122 (1934)j, a paper entitled "Acidity Titration of Low-Grade Rosins by W. C. Smith, which describes the same spectroscopic titration as the new discovery of that author. The only public result of private correspondence on the subject has been an obscure paragraph marked "Correction" [Ibid., 6 , 192 (1934)l. Mr. Smith there mentions a paper [J. IND.ENG.CHEM.,12, 274 (1920)l as being on "the acidity of red wines and fruit juices," though he was aware that half the publication, under a subheading, dealt with spectroscopic titration in general and with the use of phenolphthalein in this connection in particular, covering in itself all the ground of his own paper in every respect except as to its obvious utility in resin determinations. Mr. Smith also failed to call attention to the fact that he had attributed to others a method of examination used and Dublished by the late A. H. Allen. I greatly regret having to make publicly, for my laboratory and for an eminent dead man, claims which should have been admitted a t once. From correspondence, however, there emerges the fact that C. Gautier and P. Coursaget published a paper, '[Utilisation our l'acidimktrie du spectre d'absorption de la matihre cof)or6e en rouge violace que donne avec les alcalis la ph6nolphthalkine" [Compt. rend. SOC. b i d , 81, 733 (1918)l which in some respects anticipated the paper from this laboratory published in 1920, though following, in point of time, other articles from here [J. Soc. Chem. I n d . , 37, 117T (1918) and J . Am. Chem. Soc., 50, 873 (1918)l. I have been unable to find any notice of this paper in the abstract journals published by the Chemical Society, the AMERICAN CHEMICAL SOCIETY,or the Society of Chemical Industry. I have no access to the original paper. I am therefore unable to tell how far the published results overlap. If they do so, I wish to offer to Messrs. Gautier and Coursaget the most full apologies. I am sure these gentlemen will realize that chemical workers in this laboratory could not be expected to study journals devoted to biology. It will also be realized that, as two publications on the subject had already appeared from here, we might reasonably be considered as having a prior right to continue the line of investigation as far as we saw fit. This right was exercised, though proper notice of other workers would certainly have been taken, had their publication been available. ALFREDTINGLE CCSTOMS-EXCISE LABORATORY OF NATIONAL REVENUE DEPARTMENT OTTAWA, CANADA.August, 1934
