October, 102 i
INDUSTRIAL AND ENGINEERING CHEMISTRY
1065
The Stability of Constant-Boiling Hydrochloric Acid' By J. A. Shaw THEKOPPBRSCO., MELLON INSTITUTE
OF
THB U N I V S R S I T Y OF PITTSBURGH, PITTSBURGH, Pa.
I
T IS always a problem to determine the best method for preparing standard solutions of alkali and acid. Probably the most widely used methods employ sodium carbonate or benzoic acid as a primary standard. These require purification before use. When using sodium carbonate the required procedure for best results is rather elaborate and time-consuming. I n addition, the method does not lend itself to the use of certain indicators, such as methyl red and phenolphthalein. I n the second instance, if Bureau of Standards benzoic acid is used, the only purification necessary is dehydration. But it is often difficult, if not impossible, for a commercial chemist to obtain or keep the ethyl alcohol usually specified in this determination. There is, however, a method of preparing acidimetric standards which overcomes most of these difficulties. It consists in preparing constant-boiling hydrochloric acid and titrating weighed quantities against a solution of an alkali. This method was first proposed by Hulett and Bonner,2 and later perfected by Foulk and H~llingsworth.~The accuracy of the method is unq~estionable,~ the procedure lends itself very nicely to the conditions of a commercial laboratory, and practically any indicator desired may be used directly in the standardization. I n spite of the fact that the method has been in the literature several years, the writer knows of only one control laboratory using constant-boiling hydrochloric acid as a primary standard. On looking for the cause behind this situation it was discorered that there are no published data on the keeping qualities of this material. It has therefore been necessary to prepare the primary standard freshly each time a new standard solution is required or to engage in a longtime experiment. The average works chemist does not have the time or inclination for either. It happened that six samples of constant-boiling hydrochloric acid were available in this laboratory. These samples had been prepared from time to time and varied in age from 3 days to more than 3 years. The technic involved in their preparation was in no way better than might reasonably be expected in any laboratory. The acid distillates were caught in small Pyrex Erlenmeyer flasks and, since it was expected to use them immediately for the preparation of 1 N sulfuric acid, and not thereafter, the flasks were simply closed with a rubber stopper and labeled. Certain of these flasks escaped being discarded and for no definite reason were finally placed in a convenient closet. Most of the time they were stored in the dark. Since the room had a northern exposure only, they received no direct sunlight. It was these accumulated samples that were used for the following titrations. When it is intended to preserve the distillate for future use, it should be collected in a container of good chemical glassware with a tight-fitting glass stopper and stored in a dark closet away from sources of excessive heat. Stability Tests
I n preparing these samples of acid the barometer was read to the nearest millimeter. For the titration individual sam1 2 8
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Received M a y 24, 1926. J A m Chem S O L ,31, 390 (1909). Ihad , 46, 1220 (1823) Morey, Bur Standards, Sci. PaPer 183.
ples were weighed on an analytical balance in a Bailey weight buret in such quantities as would require approximately 40 cc. of 1 N sodium hydroxide for the titration. These samples were delivered into 150 cc. of distilled water, keeping the tip of the Bailey buret from 1 to 2 cm. above the surface of the water. (The writer has used on occasion a covered glass capsule instead of the Bailey buret.) A Bureau of Standards buret was used for the sodium hydroxide and corrections were applied for temperature variations. The buret readings were taken as nearly as possible to 0.01 cc. with the aid of a strip of black glazed paper on a piece of thin white bond paper. The results are tabulated below: Time between preparation 1 N factor of and analysis of constantSample NaOH solution" boiling HCI sample 1 1.0480 39 months 2 1.0485 34 months 3 1.0483 27 months 4 1.0480 20 months 5 1.0481 14 months 3 days 6 1.0484 Calculated from the tables of Foulk and Hollingsworth, loc. cit.
For the conditions obtaining in the average laboratory, the above figures, which do not vary more than 5 parts in 10,000, distinctly indicate that constant-boiling hydrochloric acid does not vary in strength over a considerable period of time with respect to accuracies obtainable in ordinary volumetric procedure. The works chemist should be entirely justified in preparing a quantity of it, placing in a well-stoppered bottle and using when desired. Preparation of Constant-Boiling HC1
A method for preparing constant-boiling hydrochloric acid is very completely described by Foulk and H~llingsworth.~ For the purposes of their work the apparatus ax described by them or its equivalent was necessary. The refinements mentioned in their published work, however, are entirely unadapted to use in most commercial laboratories. iifter experiment, the following procedure was substituted for that of Foulk and Hollingsworth. The only advantage claimed for it is sufficient facility for use in practically any laboratory, at the same time preserving necessary accuracy for industrial work. The two methods are not designed to meet the same need. METHOD-A distillation apparatus was set up which resembled closely the standard apparatus used for ammonia determinations. The flask was of 1 to 2 liters capacity, depending upon the amount of distillate desired. It was of the ordinary boiling flask type made of Pyrex glass, and in the top of it was placed an untrapped splash bulb. (A trap has a tendency to set up a back pressure.) This bulb was connected to a glass condenser having a 30-inch water jacket. Connections were made by means of new rubber stoppers, the inner glass tube always extending into the receiver a t least 2 cm. beyond the rubber. The internal diameter of the condensing train was never less than 6 mm. nor more than 10 mm. Superheating was prevented by placing the boiling flask in a hole in an asbestos shield. The upper part of the flask was insulated against heat radiation by means of asbestos paper. The deliTery end of the condenser was placed inside the neck of a Pyrex Erlenmeyer flask. The condenser tip
1066
INDUSTRIAL AND ENGINEERING CHEMISTRY
was not immersed in the distillate, but the condensate was allowed to fall freely into the flask. No attempt was made to close the neck of the flask for fear of setting up a back pressure. If there were ammonia fumes or much dust in the laboratory air, the receiving flask would have to be protected by being enclosed in a container of washed air. An open beaker is not recommended as a receiving vessel. For the distillation the desired quantity of ordinary C. P. hydrochloric acid was diluted to a gravity of approximately 1.10 and introduced into the flask. The distillation was carried on a t a rate not exceeding 8 to 10 cc. per minute. Under these conditions only a negligible pressure was set up in the boiling flask. The distillation must be continuous from beginning to end. The first 75 per cent of the original dilute acid that distilled over was isolated for use as a high-grade reagent, the next 10 to 15 per cent retained as standard acid, and the remaining
Vol. 18, No. 10
residue in the boiling flask discarded. The amount of this residue was never less than 100 cc. The barometric reading was taken a t the beginning of the distillation, again after 75 per cent had passed over, and finally a t the end of the distillation. The last two readings were averaged for determining the strength of the acid. Conclusion
During the last four years constant-boiling hydrochloric acid has proved exceedingly satisfactory in this laboratory as a primary standard for the preparation of solutions to be used in acidimetry and alkalimetry. Careful work has always shown the error to be much less than 1 part per thousand. Normal sulfuric acid prepared from the foregoing samples was used in cooperative work with the Bureau of Mines and several other laboratories. The results were invariably satisfactory.
Rapid Evaluation of Baked Japan Finishes' By E. M. Honan and R. E. Waterman BELL TELEPRONB LABORATORLBS, NEWYORK,N. Y.
The service life of a japan film baked on metal can be HE life of baked japan in a suitable solvent a piece evaluated by determining the rate of decomposition finishes is very uncerof metal on which the japan of the film when it is placed in an 8.5 per cent phenoltain, especially in cerhas been baked and noting water solution. The effect of the time and temperature tain kinds of service. An the length of time necessary of baking the film and the cleanness of the metal preanalysis of the uses to which to produce definite action on vious to applying the japan can also be evaluated. articles so finished are subt h e j a p a n n e d surface. A The 8.5 per cent phenol solution is a desirable testing mitted in the telephone sysfavorable feature of this type solution because its composition is quite constant at tem showed such service to of test is the elimination of ordinary room temperatures and is not changed by the the personal and mechanical involve two distinct types. evaporation of the water. variations. The most desirIn one type injury t o -the finish results primarily from a b l e s o l u t i o n having once chipping or scratching; in the other type destruction of been determined, the conditions of test can be so defined that the finish is due primarily to contact with hands, which the individual has no opportunity to interpret the results subject the japan not only to mild abrasion but also to the in an arbitrary manner. This sort of test may be used reliaction of perspiration. I n either type of service the finish ably to determine the degree of baking which a sample has may remain good for years or fail in a few months, but rapid undergone. The degree of baking in turn determines largely failure occurs much more frequently in thq second type of resistance either to mechanical injury or to attack by liquid service. Some of these variations depend not only on the contaminating agents such as perspiration. Although there severity of the service but in part on the quality of the finish are other methods of determining the degree of baking, these itself. Obviously it is highly desirable to have laboratory are usually qualitative and depend upon the color, resistance tests by which the life of japan finishes may be predicted. to scratching, or softness of the finish. In the hand-contact Several methods were devised to test the wearing qualities type of service certain liquid immersion tests may be used as a direct measure of serviceability. This was attractive to of japan finishes. These included two general types of test the writers because in certain pieces of apparatus with which corresponding roughly to the two types of service-attack by mechanical means and by action of liquid reagents. they were concerned it had become apparent that the finish failed most rapidly where it came in contact with the hands. Combinations of these two types were also tried. The mechanical tests included rubbing, scratching, bending, Experimental and determination of physical constants of the films. Tests An attempt was therefore made to simulate such action of this type seemed to be of possible utility where abrasion and chipping are important factors in the service. Much work by immersing test pieces in liquids that might be expected to was done on these various tests, but all were found to possess resemble perspiration. A solution was made up approxiinherent defects. The conditions under which such tests mately as follows: water 98.59 parts, oleic acid 0.01 part, must be conducted are necessarily restricted. The interpre- sodium chloride 0.15 part, urea 0.14 part, acid sodium sulfate 0.03 part, monosodium phosphate 0.003 part, potassium tation of the results depends upon the strict maintenance of these conditions and on the judgment of the individual con- chloride 0.06 part; neutral fat 0.01 part. Samples were also ducting the test. Therefore, after many trials it was decided immersed in commercial oleic acid and in solutions of vato abandon this type of test for the present, even for cases rious individual inorganic salts of various strengths. In in which mechanical injury is anticipated to be important. most cases a correlation was observed between the degree of The liquid type of test may consist simply in immersing baking and the time required to soften the film. For example, a two-coat sample baked 2 hours at 175' C. became soft in Received M a y 24, 1926. Presented before the Section of Paint and oleic acid in 22 hours, and a two-coat sample baked 2 hours Varnish Chemistry a t the Midwest Regional Meeting of the American at 200" C. failed only at the end of 430 hours. I t was found, Chemical Society, Madison, Wis., May 27 to 29, 1926.
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