BERNARD M. MITZNER Chemical Warfare Laboratories, Army Chemical Center, Maryland ~ R is E a great deal of diversified opinion about possibly the most overlooked subject in quantitative analysis, drying volumetric glassware. The analyst usually employs the techniques that have been learned in elementary quantitative analysis courses without realizing the controversial nature of this subject, especially in regard to the application of heat as a drying measure. Fahles and Kennyl are quite opposed to the application of heat for drying purposes for they say in their textbook, "In no case should the use of hot water or the application of heat to volumetric apparatus be resorted to, because it may bring about a permanent enlargement in the vessel, due to thermal 'after effects.' " They suggest rinsing the flask with alcohol in order to facilitate drying. On the other hand, Willard and Furman2 suggest employing acetone to facilitate drying and advise against using alcohol or ether. They make no mention regarding the avoidance of heat; however, they do suggest employing cleaning solution heated to 100°C. (which is a temperature that would tend to dry laboratory glassware quite well), although many other authors advocate the use of cold cleaning solution. Kolthoff and Sande113 advocate both alcohol and acetone for drying purposes and suggest that it is not permissible to hasten the drying procedure by heating because slow changes in volume may occur after cooling. A fairly simple but somewhat time-consuming experiment has been carried out with 50-ml. Pyrex volumetric flasks. Eight were chosen a t random and were carefully cleaned by washing with cleaning solution a t room temperature and rinsed with distilled water. They were allowed to dry without the aid of either heat or solvents and their volumes were carefully calibrated. The flasks were then placed in a laboratory oven a t a temperature of 100°C. for 24 hours, removed and allowed to come to room temperature over a period of six hours, and then recalibrated. The same procedure was followed for temperatures of
~FAHLES, H. A., AND F. KENNY,"Inorganic Quantitative Analysis," D. Appleton Century Co., Inc., New York, 1939, p. lA lwd 7.
WILLARD, H. H., AND N. H. FURMAN, "Elementary Quantitative Analysis (Theory and Practice)," D. Van Nostrand Co., Inc., New York, 1940, p. 106. "OLTHOFF,I. M., AND E. B.SANDELL, "Textbook of Quantitative Inorganic Analysis," The MacMillm Co., New York, 1943, p. 531.
150°C. and 200°C. The results of the recalihration were all identical with the original measurements. There was no apparant change (10.01 ml.) in the volumes of the flasks as a result of heating, although the 200°C. temperature was far in excess of the temperature maintained by the average laboratory oven. The author originally intended to prepare curves to demonstrate graphically the results of the experiment. However, due to the highly reproducible negative results that were obtained, it would be a uraste of precious space. Another experiment was performed employing the three solvents discussed previously (acetone, ether, and alcohol) in order to determine their value as a drying aid. The volumetric flasks were rinsed with distilled water, and, while still wet, 5-ml. portions of acetone were added, swirled about, and emptied. The flasks were allowed to dry in a partially inverted position without the application of heat for a period of 24 hours. In order to determine the relative speed of drying, 1-gm. portions of talcum were added to one of the flasks at a definite time interval and the vessel was shaken. The talcum was emptied by turning the flask upside down and gently tapping. The amount of talcum adhering to the walls of the vessel was an indication of its relative dryness. The same procedure was carried out with alcohol and ether. Acetone was found to facilitate drying in the shortest period of time. Alcohol was somewhat less effective and ether was found to be the poorest drying aid. CONCLUSIONS
(1) The application of heat (150°C., employed in most laboratory ovens) to volumetric glassware has in no way been found to be detrimental. (2) The application of heat appears to be a highly effective method and is neither costly nor time consuming, i.e., makes glassware available for repeated use in the minimum amount of time. (3) No adverse effects were obtained when solvents were employed. (4) One has to agree with most authors that in a majority of applications volumetric glassware need not be dried before use (except when certain organic liquids are employed and for calibration purposes). When the volumetric flask is rinsed several times with the liquid to he employed, one will invariably obtain results equal t o those obtainable with a perfectly dry flask.