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curves for interpolation of results, thus saving the time and plates required for making individual curves from the results on each plate.
Literature Cited (1) Cholak, J., J . Am. Chem. Soc.. 57, 104 (1935). (2) Gerlach, w., and Schweitser, E., “Foundations and Methods of Chemical Analysis by the Emission Spectrum,” London, Adam Hilger, Ltd., 1929. (3) Lundegardh, H.,“Die quantitative Spektralanalyse der Elemente,” Part 11, Jena, Gustav Fischer, 1934.
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(4) Lusk, G., “Science of Nutrition,” 3rd ed., p. 360, Philadelphia, W. B. Saunders Co., 1919. (5) Mannkopff, R., and Peters, C., 2. Phgasik, 70,444 (1931). (6) Mathews, A. P., “Physiological Chemistry,” 5th ed., pp. 730, 1186, 1187, New York, Wm. Wood and Co., 1930. (7) Nitchie, C.C., and Standen, G. W., IND.ENG.CHEM.,Anal. Ed., 4, 182 (1932). (8) RabinowitCh, 1. Dingwall, A.8 and Maokay, F. H.9 J. Bid. Chem., 103, 707 (1933). (9) Scheibe, G., and Neuhausser, A., Z.angew. Chem., 41,1218(1928). RECEIVED March 18, 1935.
Volumetric Determination of Evaporation Rates L. A. WETLAUFER AND J. B. GREGOR E. I. du Pont de Nemours & Co., Inc., 3500 Grays Ferry Ave., Philadelphia, Pa,
HE development of modern protective coatings, parnounced by Lowell (4, called the Evap-0-Rotor, requires titularly since the introduction of many of the now the usual analytical weighings. It employs a turntable with common synthetic resins, has emphasized the imporcapacity for several samples, the table being protected tanceof the evaporation rates of the solvents and thinners by a shield several inches high to minimize the effect of used in their manufacture and application. A greater variety stray air currents. The table slowly rotates, establishing a of materials, a more rigid control of finished product properconstant air flow which removes the heavy vapors from the ties, and the development of fast-drying enamels have all evaporating surfaces. This method is believed to be one of the most satisfactory of the gravimetric procedures developed been contributing factors. All of the present methods for determining evaporation to date in that a number of samples may be evaporated sirates with which the authors are familiar are gravimetric. In multaneously, and that a simple method of air regulation is the usual procedure 1 to 2 grams of the liquid are placed in a employed. For the slower evaporating liquids, however, the tared dish such as a friction-top can cover and weighed a t intertime and labor factors are undesirable for routine control vals during the period of evaporation. Those which employ work. a special balance with sample suspended, thus doing away At best any method for measuring the rates of evaporation of liquids is not a precise criterion of how these liquids will with tedious analytical weighings, are open to the criticism that only one or two samples can be measured at a time. affect the drying time of finishes. Many factors which affect Perhaps the best known of these special instruments is the evaporation rates will affect drying time in different ways. Hart evaporation balance (g), a device equipped for one samDurrans (1)points out that vapor pressure, heat conductivity, latent heat of evaporation, molecular association, surface ple. Another special instrument, the Jolly balance (S), is equipped for two samples but, according to the method, retension, and humidity are important considerations. He points out further that in mixtures of liquids the molecular quires a determination of a standard at the same time as the attraction of one component by another and the depression sample. It would be necessary, therefore, to use several units of these special instruments in order to conduct a numof the vapor pressure of one component by another are likeber of tests at one time, thus involving a considerable investwise governing factors. Solvent power and vapor density should be added to the list. A study of the comparative ment in equipment. Another difficulty encountered with most gravimetric rates of evaporation is therefore of value only in a general methods is the control of air flow over the exposed area of the sense. In the formulation of a product, selection of likely solvents or thinners can, of course, be made from graphs sample. Wilson and IVorster (6) attempted to overcome this feature by the use of a special tunnel in which the samples which express these data, but the materials so chosen must be thoroughly evaluated in the are placed and through which a constant flow of air is conformula in order to establish the one or the blend ducted, This procedure, of course, r e q u i r e s m a n u a l which most nearly satisfies the p r o p e r t i e s r e q u i r e d . analytical weighings a t interThe most specific value to vals, and is one of the things be gained from evaporation which the special balances, data appears to be that of such as the Hart and the controlling the uniformity Jolly, overcame by making of a given liquid as received the weighings a u t o m a t i c . Also in t h e Wilson a n d by the consumer, a n d of Worster method it is adblends which may be premittedly difficult to control pared prior t o manufacture. the current of air with a good With these things in mind degree of accuracy. AnFIGURE 1. DISTILLATION CURVES t h e a t t e m p t to establish a o t h e r device recently an-
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rapid, simple, and sufficiently precise method for measuring separation of traces of water. Solvents in this range are beevaporation rates was approached primarily from the standing investigated further and the work may culminate in the point of control of uniformity. One may rightly inquire why application of air a t an initial temperature above 25" C., distillation range control should not suffice for this purpose. since for comparative purposes it is desirable to measure all It is found, however, that samples of a liquid which show good solvents by the same method. However, should the evapouniformity in this respect do-not always show the sameuniformity in evaporation characteristics and in fact may even show a reversal of the expected. For example, a recent shipment of a petroleum solvent had a distillation end point of 179" C. and an evaporation end point of 80 minutes. A later shipment had a distillation end point of 185OC. and an evaporation end point of 58 minutes. Both were otherwise essentially the same in distillation percentages. An enamel containing the faster evaporating of these had a "tack-free" time of 4 hours, whereas the slower evaporating solvent caused a 15minute increase in drying to this stage. It is found also tha,t two liquids having essentially the same distillation dry point may have evaporation end points quite widely separated. No. 1 petroleum naphtha and No. 2 petroleum naphtha shown in Figures 1, 4,and 5 are an outstanding example. A quick-drying enamel dried to the tack-free stage in 3 hours with the faster evaporating of these two solvents as against 3.5 hours with the other. FIGURE 2. EVAPOROMETER Further, in connection with distillation-evaporation Th,e tubes are in horizontal position for evaporation and are moved to vertical position for volumetric observation. comparisons among solvents whose chemical composiA . Air blower D. Manometer tion is distinctly different, distillation curves do not in B. Trap E . Gas distrjbutor all caseti occur in the same order as evaporation curves C. Drier I". Evaporation tubes even within rather wide limits. The Dosition of gum turpentine with respect to petroleum solvents among the rometer prove to be impractical here, the gravimetric method distillation curves in Figure 1, as compared with its position from the standpoint of rapidity is applicable for control puramong the evaporation curves in Figures 4 and 5, is illustraposes, and it is believed that the Evap-0-Rotor mentioned tive of this point. From the standpoint, therefore, of general above should be very satisfactory for these liquids. To put usefulness for formulating work as well as control of uniit another way, the evaporometer should be found of greatest formity, the evaporation data are by far the most desirable. interest for the average run of paint and varnish solvents and The a:pparatus described in this paper and referred to herethinners and the Evap-0-Rotor for lacquer solvents and after as the evaporometer is believed to be novel in that its thinners. basic principle is volumetric.
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Briefly, the assembly of the evaporometer as shown in Figure 2 consists of an air blower, a sulfuric acid wash bottle for drying
the air, 5 manometer, a gas distributor, and graduated sample tubes. 'The tubes of tapered form are in horizontal position with the sample spread out over maximum area during evaporation, and in vertical position at periodic intervals for volumetric observations. Reasonably good duplication of results is obtained, and the time for each test is short enough for routine control, complete evaporation data being obtained on the average in about one-eighLh of the time required for the usual gravimetric procedure. The present apparatus is equipped with three sample tubes, but is limited to this number only by the capacity of the air blower in use. Rubeok and Dah1 (6) have shown that for c. P. benzene and petrobenzol variations in humidity normally encountered do not appreciably affect results. Work done by the authors has indicated that this is not true for all solvents and thinners, hence it appears desirable for the present a t least to maintain a humidity control. The evaporometer method is not presented as all-inclusive, since exloerimental work has been largely confined to liquids having evaporation end points equal to or greater than industrial xylol, eliminating from primary consideration extremely fast-evaporating solvents such as toluene, ethyl alcohol, and 20" benzine. Effort was concentrated on the slower evaporating types, because for them gravimetric methods are time-consuming and difficult to handle in a routine control laboratory. Preliminary work in the range of the fast-evaporating liquids indicates a very appreciable lowering of the temperature during evapocation, causing in some cases a clouding of the liquid which may be due to
Apparatus and Method The evaporometer assembly is shown in Figure 2. The air blower is a Boehnke rotary air blast and suction apparatus producing a maximum pressure of 844 grams per sq. om. (12 pounds per square inch). The acid wash bottle for drying the air is an ordinary 4-liter Pyrex bottle, the lead toward the sample tubes passing through a trap containing glass wool. Beyond the trap is a water manometer. The evaporation tubes are attached t o a three-way gas distributor to insure equal distribution of air. The tubes are graduated oil centrifuge tubes with ta ered bottom, in accordancewith A. S. T. M. specificationsfor testsb-91-30Tand D-96-30. These tubes are made by a number of manufacturers, but the conical dimensions vary among the makers. Those manufactured by the Kimble Glass Company of Vineland, N. J. have been adopted as standard, since they are very uniform and appear to have the clearest glass and the most distinct graduations. No. l two-holed rubber stop ers are used with the tubes, one hole carrying the intake anzthe other functioning as the exhaust. The tubes are held in position by buret clamps which in turn are mounted on a rod suspended between two ring stands. The gas distributor is suspended above the tubes from a universal clamp. The apparatus can be set up as described for about seventy-fivedollars. The evaporometer a t present is operated in a constanttemperature room maintained at 25" C. It may be operated outside of a constant-temperature room, however, with good duplication of results either by running a standard each time with samples, or by connecting the air line to a coil immersed in a thermostatically controlled water bath, the latter method supplying air of constant temperature to the sample tubes.
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bottom during the observaIt is desirable in this case, tion of volume. To deterhowever, to temper the sammine this residue, in order ples in the tubes before startthat the volumetric data may ing the test. be used, it should be done The method of determinagravimetrically and the volution requires no special skill metric curve carried to this or scientific knowledge. Two milliliters of the sample a r e p o i n t . The application of placed in one of the tubes and t h i s p r o c e d u r e for liquids t h e t u b e s clamped in horicontaining nonvolatile zontal position. With the air m a t t e r h a s t h e advantage blower in operation and the manometer adjusted to 20 om., over the c o m m o n g r a v i the stopper is inserted in the metric method in saving of tube neck. All t u b e s a r e labor, since volumetric obc o n n e c t e d during operation servations require but a few whether in use or not, in order to maintain equal air distribuminutes and the residue retion at all times. The exactFIGUFIE 5. EVAPORATION RATESBY USUALGRAVIHETRIC q u i r e s b u t one weighing if ness of the horizontal position METHOD the sample is allowed to stand is controlled bv observing the for about an hour beyond the point where the area of the surface of the liquid appears perfectly symmetrical. normal evaporating time. The actual labor on solvents of At intervals, depending upon the speed of evaporation of the this nature is about one-half of that required for the gravisolvent under test, the tube is brought to the vertical position metric test. On liquids containing no residue the volumetric and the solvent allowed to drain from the side walls for 1 minute. method reduces labor about two-thirds. During this 1-minute period, the meniscus is brought to the level position by slight adjustments of the tube until the maximum The curves obtained by the two methods, while they bottom curvature of the meniscus is centered in the tube. At the are in the same general order, do not exhibit identical proend of the minute, the volume is read with the aid of a magnifying portions of order. This, however, is true of any two graviglass, and the tube immediately returned t o the horizontal metric methods which differ appreciably in mechanical setposition. All readings are recorded together with the elapsed time. The final reading is taken at approximatelythe 98 per cent up or in conditions surrounding the test, such as the rate a t point, since beyond this point the solvent curve does not alter which the vapors are removed from the evaporating surface. appreciably in slope and can be extrapolated with greater acThe latter is believed t o be the principal factor involved. In curacy than can be gained by making further readings. As a the application of finishes industrially where efficient ventilamatter of convenience, a chart listing the graduations from 0 to 2 ml., together with the percentage correaponding t o each graduation systems are used, the vapors are being constantly retion, has been prepared for routine use. With normal care, moved from the surface of the film in a manner more like that duplication of results t o within *3 per cent from the mean figure in the evaporometer than in any of the gravimetric methods, of a series of determinations can be obtained on a given sample. with the possible exception of those described by Wilson and Triplicate results on two solvents are shown in Figure 3. Worster (6) and by Lowell (4). Another consideration in Time-volume graphs of a number of common solvents are this connection is that of all surfaces coated a high percentage shown in Figure 4, and may be compared with the curves obare in vertical position during the drying period, and the tained gravimetrically, which are shown in Figure 5. The vapors, being heavier than air, rapidly leave the surface. In gravimetric data were obtained by evaporating the liquids in the ordinary gravimetric procedure where the vapors remain 0.5-liter (1-pint) friction-top can covers and making analytiover the surface of the liquid, a depressing effect on the rate cal weighings a t intervals. of evaporation is established. Methods, therefore, in which the vapors are constantly removed are believed to be the most practical. Discussion of Results In view of these considerations it appears that the greatest It will be noted in Figure 5 that the curve for gum turpenvalue of the evaporometer lies in the primary consideration tine shows a 3 per cent residue, which is not indicated in the which prompted this development-namely, that of reducing volumetric data in Figure 4. I n the volumetric method when the time and labor. required for measuring evaporation rates, the final reading is made this residue does not drain to the particularly for the slower evaporating types, with the added
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advantage over the usual gravimetric method that the vapors are constantly removed from the evaporating surface.
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Acknowledgment The authors are indebted to C. F. Rassweiler and H. H. Hopkins, under whose jurisdiction this work was conducted.
Trends in the field of protective coatings emphasize the importance of the evaporation rates of the solvents and thinners used in their manufacture and application. A survey of existing methods reveals that for the slower evaporating types they are time-consuming, lacking in control of air flow, temperature, and humidity, or costly to establish for control purposes. d volumetric method has been described which is rapid, sufficiently precise for control purposes, reasonably inexpensive and which embodies positive control of air flow, temperature, and humidity. The results so obtained, by virtue of the constant removal of vapor from the evaporating surface, are believed to be somewhat more practical than those obtained by methods in which this feature is lacking.
Literature Cited (1) Durrans, T. H., “Solvents,” New York, D. Van Nostrand Co., 1930. (2) Gardner, H. A., “Physical and Chemical Examination of Paints, Varnishes, Lacquers, and Colors,” 6th ed., pp. 701-3, Washington, Institute of Paint and Varnish Research, 1933. (3) Ibid., p. 703. (4) Lowell, H. J., IND. ENQ.CHEM.,Anal. Ed., 7, 278 (1935). (5) Rubeck and Dahl, Ibid., 6,421 (1934). (6) Wilsonand Worster, IND.ENG.CHEW,21, 592 (1929). R E C ~ I V EJune D 7, 1935. Presented before the Diviaion of Paint and Varnish Chemistry a t the 89th Meeting of the American Chemical Society, New York,N. Y., April 22 t o 26, 1935.
Determination of Mercury in Iodinated Organic Compounds of Mercury I J
Application of Spacu and Spacu Copper Sulfate Propylenediamine Reagent R. B. SANDIN
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E. T. MARGOLIS, University of Alberta, Edmonton, Alberta, Canada
HE determination of mercury in mercurated organic
compounds is of considerable importance, because of the increasing use of such compounds in medicine. Numerous procedures are available, but in the majority of them the halogens and especially iodine are interfering elements and must be gotten rid of. In the potassium thiocyanate titration of mercury, all the halogens must be absent and to accomplish this Kharasch and Flenner (3)have developed a very satisfactory method. If iodine is present, mercury cannot be precipitated by Jamieson’s reagent, but the procedure of Fenimore and Wagner (3) obviates this difficulty. Finally, in the determination of mercury as the sulfide, iodine must be removed by such methods as those of Dunning and Farinholt (1) and Tabern and Shelberg (5). In three of the above procedures (2, 3, 5 ) interfering halogens are eliminated by precipitating the mercury in solution as metallic mercury, which is then redissolved and determined by an appropriate method. Recently Whitmore and Sobatzki (6) have developed a new and very direct method for the determination of mercury in organic mercury compounds such as organomercuric halides, by which none of the halogens are interfering elements. Because of the difficulty mentioned above, it was thought that an adaptation of the method of Spacu and Spacu (4) might have possibilities. This paper describes a satisfactory procedure, whereby organic mercury in the presence of iodine is finally determined by the copper sulfate-propylenediamine reagent. The organic mercury compound containing iodine is oxidized in a bomb tube by the well-known Carius method. However, a method of oxidation such as that of Tabern and Shelberg (5) should be satisfactory, provided mercuric iodide is not allowed to escape. The only special reagent required is propylenediamine which is obtainable from the Eastman Kodak Company as a 70 to 75 per cent aqueous solution. The copper sulfatepropylenediamine reagent is prepared by dissolving 2.5 grams
of crystalline copper sulfate in water, then adding 2 grams of the propylenediamine solution. It should be made up as needed.
Procedure Weigh out a sample, corresponding to at least 0.3 gram of mercury, in a small Pyrex weighing tube similar to that used in the Carius halogen determination. To a Carius bomb tube add 3 cc. of fuming nitric acid, transfer the weighing tube carefully to the bomb tube, and proceed as in a halogen determination. After the bomb tube hab been heated and cooled (and before opening), heat the capillary end of the bomb tube gently with a gas flame (using goggles), to prevent the loss of any mercuric iodide, which has condensed in that part of the tube, when the capillary is opened. Cut off the end of the tube, add 20 cc. of water and 15 cc. of concentrated ammonium hydroxide, and an amount of solid potassium iodide (plus an excess), sufficient to dissolve the mercuric iodide. Transfer the solution to a 400-cc. beaker and wash out the bomb tube thoroughly with water. Do not allow the total volume t o exceed 200 cc. If the solution is brown, owing to free iodine, carefully add clear dilute sodium hydroxide solution until the color is a pale yellow. Heat the solution t o boiling and add an excess of hot copper sulfate-propylenediamine reagent. Cool for several hours in an ice-water mixture. Filter the blue precipitate on a weighed Gooch crucible and wash from three to four times with an aqueous solution containing 0.1 per cent of potassium iodide and 0.1 per cent of the copper sulfate-propylenediamine reagent. Then wash three to four times with 2-cc. portions of 96 per cent alcohol and finally two t o four times with 2-cc. portions of ether. Dry in a vacuum desiccator and weigh. The precipitate contains 21.81 per cent of mercury. Considerable preliminary work was carried out t o determine whether the method would be satisfactory. A few typical analyses, listed in Table I, are the average of two or more closely agreeing determinations, and indicate the real value of the method. The calculated percentage of mercury is given for compounds I and I1 which were pure. The remaining compounds were of unknown purity and, for that
