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ISDCSTRIAL An'D ENGINEERING CHEMISTRY
Vol. 18, No. 12
Separation and Analysis of the Volatile Solvents and Thinners of Lacquers' By Ray M. Carter U S INDUSTRIAL ALCOHOLCo
Separation of Solvents a n d Thinners ISTILLATION seems to be the best method for the recovery of the volatile constituents of lacquers in a form which lends itself to subsequent examination. The sample of lacquer, preferably about 200 cc., is placed in a distilling flask fitted with a steam inlet and a good condenser. The temperature is slowly raised, the flask being immersed nearly to the side arm in an oil bath. The maximum bath temperature is 120" C. At high temperatures the nitrocellulose may decompose, often with a quick puff, liberating large quantities of nitrous oxide, and the resulting distillates are generally contaminated, run high in free acid, and are not conducive to good results. When the distillate ceases to come over a t 120" C., distillation with steam is used to bring over the higher boiling sohents and all other materials which distil with steam. Due notice of this must be taken in later analyses in order not to confuse high-boiling solvents a n d plasticizers. The distillate obtained by means of steam usually settles in two layers; the upper one, consisting mainly of ester, is removed, and the lower or water layer is saturated with calcium chloride or, preferably, sodium sulfate in order to throw out of solution as much of the dissolved solvents as possible. The saturated salt solution may be distilled if necessary in order to separate the last trace of dissolved solvent, but this is not usually necessary. The two ester fractions may now be combined or they may be examined separately. Usually the amount of ester obtained by steam distillation is small and will best be combined with the earlier distillate, all subsequent tests being made on one sample, but occasionally it is best to examine the two distillates separately. If the combined distillate is not dry it should be made so with sodium sulfate. A second distillation is necessary in order to remove dissolved salts before the application of chemical tests. Examination of Distillate The following determinations will be run on the distillate as a matter of routine: (1) odor, (2) specific gravity, (3) boiling range, (4) saponification, (5) solubility in concentrated sulfuric acid, and (6) solubility in water. Many other tests may have to be made, but those given above form the basis for a chemical evaluation and are often all that are necessary. ODOR-From the odor of the distillate the analyst will make his original estimate of what materials are present, using the succeeding tests to confirm his judgment. SPECIFICGRAVITY-specific gravity is generally determined with a pycnometer. The temperature standard may vary in different laboratories, but it should always be that at which similar determinations have been made on various individual solvents and thinners. The specific gravity determination on such complicated mixtures as are usually obtained is of little value, but serves admirably to check other observations. BOILINGRANGE-A knowledge of the boiling range is of
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1 Presented as a part of the Symposium on "Analysis of Lacquers" before the Midwest Regional Meeting and the Meeting of the Section of Paint and Varnish Chemistry of the American Chemical Society, Madison, Wis.. May 27 to 29, 1926.
BALTIMORR, ID.
primary importance. It is absolutely necessary that the mixture be dry before distilling as water will form constantboiling mixtures and upset all deductions based upon consideration of boiling range. I n determining the boiling range one has a choice of two methods: (1) a simple distillation using no fractionation, and ( 2 ) a more complete fractional distillation using a high rate of reflux and repeating the distillation until constant results are obtained. The proportion of the various materials present will largely be limited by a consideration of either their price or solubility and in many' cases simple distillation gives the analyst all the data necessary. The apparatus specified in the Bureau of Mines method for gasoline distillation is very satisfactory for this type of work. Temperature readings are taken for the first drop, each successive 5 cc., and for the dry point. Whenever an exact quantitative and qualitative analysis is required, the analyst must resort to fractionation of the sample through some efficient column-that is, one which will allow of a high reflux ratio and which will not hold back too large an amount of the small sample a t the close of the distillation, A rod-and-disk type of Young's column has been found to work satisfactorily. The fractionation may have to be repeated several times before a good separation is obtained between substances of practically the same boiling point-for example, ethyl propionate (b. p. 99.1" C.) and n-propyl acetate (b. p. 101.6" C.). The number of separate fractions to be collected in this more accurate distillation will depend upon the boiling range itself and must be left entirely to the discretion of the analyst. The results of the boiling range determination are much more instructive when the amounts of the various fractions are plotted against the corresponding temperatures. If the chart is made to show the boiling points of the usual solvents and diluents the evaluation of the tests becomes still easier. SAPONIFICATION-The saponification of the sample ranks next in importance and is carried out in the usual manner. One to two grams of the sample is saponified with alcoholic potash, using the pressure bottle method and the caustic consumption calculated to the most probable ester as evidenced by the odor of the sample and the boiling range. SOLUBILITY IN H2S04-The solubility of the distillate in concentrated sulfuric acid gives a measure of the hydrocarbons present. Two volumes of acid to one volume of sample is sufficient. The mixing must be carefully done, avoiding local heating. After thorough shaking and settling, the volume of material insoluble in sulfuric acid is determined and the percentage of hydrocarbons calculated. This method gives low results, but may be corrected by an approximate factor. Odor is usually sufficient to identify the hydrocarbon, but in case of doubt the hydrocarbon layer may be separated, neutralized, and distilled for its boiling range and other suitable tests applied. If fusel oil is present as a diluent i t will probably be identified by odor. Its determination is difficult, but an approximate figure may be obtained by saponification and acetylization of the fraction in which the fusel oil accumulates on fractionation. SOLUBILITY IN WATER-The solubility of the distillate in
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water is mereIy a confirmatory test, a high solubility indicating high alcohol content, although the presence of ethyl lactate increases the solubility in water. There would be no difficulty, however, in distinguishing between dcohol and ethvl lactate bv examination of the boiling range curve. SolLbility in t6ree volumes of saturated sEdium- chloride solution gives an indication of the amount of’ methanol, ethyl alcohol, and acetone present.
whether the actual constituents are monatomic alcohols or hydroxy esters such as ethyl lactate. Here again the boiling range curve will help in making correct deductions.
Correlation and Evaluation of Results
METHANOL-Chapin-Elvove test, or the prussic acid method ALKYLCARBONATES-Determination of the carbonate formed by saponification ALKYLLACTATE-oxidation with permanganate and determination of the acetaldehyde formed ALKYL OXALATES-Saponification and determination of oxalate radical ACETONE-Messenger or hydroxylamine method
The correlation of the results of the various tests is by no means easy. The greatest help is a fund of experience gained by working with solvents in various mixtures. The boiling range indicates which of the various solvents may be expected and in combination with the saponification value one can estimate quite accurately what materials are present and how much of each. Exact figures for the composition of a lacquer cannot be expected to result from the usual examination such as here outlined. For instance, no known method will distinguish between butyl acetate and amyl acetate with the accuracy that we can distinguish between butyl acetate and butyl alcohol. For this reason t h e composition of a lacquer as the result of an analysis can best be expressed as varying within certain limits. The total hydroxyl group can be ascertained by acetylization, but the method is useless as a means of determining
Special Tests
Special analytical procedures can be applied in the case of certain solvents, which Serve as definite of the amounts of these various constituents. For example:
ORGANICAcrDs-It sometimes becomes necessary to determine what organic acids are present in combination. The best method of carrying out such an investigation lies in the use of the Duclaux distillation scheme. A dilute aqueous solution of the free organic acids is distilled under definite conditions. As was shown by Duclaux, each volatile fatty acid distils from an aqueous solution a t a definite rate, regardless of the presence of other similar acids, and in this way it is possible to determine what organic acids are present. The method is of value only in the hands of an analyst thoroughly experienced in the technic of the procedure.
Some Effects of Ultra-Violet Light on Paint Vehicles’ By George F. A. Stuta THE N E W
JERS8Y
ZINC
HE effectiveness of blue and ultra-violet light in accelerating the drying of an oil film is generally recognized.2 The effect of such light in accelerating the destruction of the film is also well established.3 The present paper reports some results obtained in an investigation of the mechanism of this accelerating action displayed by ultraviolet light. It seems probable that the decomposition, or “weathering,” of a n oil film is simply a continuation of the drying of the film, and hence the same reaction or series of reactions must be involved in both.
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Method
The effect of ultra-violet light on a mass of wet oil has been studied by placing about 300 cc. of oil in a 400-cc. flask of
Figure 1-Apparatus
for Determining L i g h t Absorption b y Oil
clear fused quartz, and exposing it to a Cooper-Hewitt quartz Uviarc a t a distance of 30 cm. (12 inches). The oil was 1 Presented before the Midwest Regional Meeting and the Meeting of the Section of Paint and Varnish Chemistry of the American Chemical Society, Madison, Wis., May 27 to 29, 1928. 2 Gardner, Paint Mfrs. Assoc. U.S., Tech. Circ. 172. 8 Nelson, Proc. Am. SOC. Testing Materials, 22, P t 11, 485 (19221; Nelson and Schmutz, I b i d . , Pt. 11, 920 (1924).
CO., PALYBRTON, P A .
stirred continuously with a small glass stirrer, and a slow stream of air, oxygen, or nitrogen bubbled into the oil. The temperature stayed nearly constant, at about 50’ C. The oil was sampled a t intervals until it had attained a considerable body. The viscosity of the several samples was determined by use of the Gardner-Holt tubes and, in the case of t h e samples beyond the range of the tubes, the result was obtained by timing the rise of the air bubble in the tube and assuming the rate of rise to be inversely proportional to the viscosity.4 The molecular weights were very kindly determined by J. S. Long, of Lehigh University, using the freezing point method.6 As a further means of studying the action of ultra-violet light and the changes it accelerates, the degree to which such light is absorbed by the oil was measured. This absorptioon was determined in the wave-length interval from 3655 A. to 2300 A., using a n ultra-violet spectrophotometer. A diagram of the apparatus, as used, is shown in Figure 1. Light from the quartz Uviarc lamp passes through the quartz cell containing a thin film of oil and is dispersed in the Bausch & Lomb quartz monochromator. I n order to measure visually the intensity of the ultra-violet light transmitted, A. H. Pfund suggested the use of a thin screen of fluorescent uranium glass cemented to a clear glass prism. The screen is viewed from above a t a n angle of 60 degrees or more, the lens L rendering parallel the light from the foreshortened image of the slit. When so viewed the fluorescent light is particularly brilliant, and is easily photometered by means of the Macbeth illuminometer. The intensity of the fluorescent light is proportional to the intensity of the radiation falling 4 6
Barr, Phil. Mag., 1, 395 (1926). Long and Smull, THISJ O U R N A L , 17, 138 (1925).
