INDUSTRIAL A N D ENGINEERING CHEMISTRY
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the unstirred samples was considerably greater than the others showing clearly the effect of agitation in keeping up the gelling point. Of the stirred samples, the one containing chrome alum dropped slightly more rapidly during the first few hours, after which the gelling points of the two were practicaIly parallel for a period of four days. This would seem to indicate that the drop in gelling point is really characteristic of the glue alone. For a given concentration, therefore, the effect of chrome alum is to raise not only the initial gelling point, but the whole curve as well. The more rapid drop of the unstirred sample containing chrome alum was due possibly to a separating out of a gluechromium precipitate, thus leaving a solution weaker in glue and in chrome alum. The presence of a visible sediment was noted in this instance.
and permits rapid drying without draining to the bottom or fermentation, regardless of the temperature.
ACKNOWLEDGMENT The writers desire to acknowledge the courtesy of the Vacuum Oil Company in permitting the publication of these results, and to express their appreciation of the helpful cooperation of the members of the Rochester laboratory and plant in this investigation. The writers also are indebted t o Dr. S. E. Sheppard for several helpful suggestions in connection with the preparation of the paper.
A Simple Demonstration of the Effect of Temperature upon a Gas‘ By Charles DeWitt Hurd UNIVERSITY OF I L ~ I N O I S ,U R B A N A ,
FIG.
DROP IN GELIJNGPOINT WITH
OF
GLUEA N D GLUE-CHROME SOLUTIONS
[email protected] HELDAT 160’ F.
The curves in Fig. 5 are not strictly comparable, since the glue-alum mixes contain only 35 per cent glue. With equal amounts of glue the gelling-point curves would have a still greater spread. Other samples of glue and glue-chrome-alum solutions were stirred and kept hot for a few hours each day, and were allowed to cool to room temperature during about 16 hrs. per day. These samples showed no appreciable gellingpoint lowering for nearly 48 hrs., when mold started to form. It is apparent, then, that the gelling point drops much more rapidly when the solution is kept above its gelling point. By adding varying percentages of chrome alum to a gluealum solution, the gelling point of which had dropped, it was found possible to restore the gelling point to its original value. About 70 or 75 per cent as much alum was required to make a given increase in gelling point as was required for fresh glue. Thus for any glue-chrome alum mix, the addition of small amounts of chrome alum with agitation once or twice a day serves to keep the solution up to the required gelling point. With these precautions and control of the temperature of the solution so as to get the proper thickness of glue coat, entirely satisfactory results were obtained in the plant. The method is now used as standard practice during hot weather
VOl. 15, No. 4
ILL.
Although every beginner in chemistry is usually drilled in the mathematics of the gas laws, very few are ever given the opportunity to demonstrate the laws by experiment. This is probably due to the fact that the experiments which would be assigned are quantitative in nature, and as such would involve the use of apparatus somewhat too complex for the novice in laboratory procedure. The two experiments which follow do not aim to prove Charles’ Law, since they are qualitative in nature. They do demonstrate, however, that a gas will contract with a decrease in temperature and will expand with an increase in temperature. The apparatus, certainly, would not confuse even a beginner. Six grams of soap are added to 80 cc. of distilled water in a tall 100-cc. beaker. The mixture is heated nearly to boiling until the soap is entirely dissolved. A test tube is warmed, and at the same time the inner wall of it is lubricated by filling it with the hot soap solution. This soap solution is immediately poured back into the beaker, and a soap film is formed across the mouth of the tube. This can be done easily if the mouth of the tube is dipped just below the surface of the solution and then withdrawn. This film will rise in the inverted tube as the tube cools. It can be made to rise rapidly if the walls of the tube are surrounded by a cold, wet cloth. This shows the contraction in volume due to a decrease in temperature. It is simple also to demonstrate gaseous expansion due to an increase in temperature. A soap film is formed across the mouth of a cold test tube. If the rounded glass end of the tube is thrust into the hot soap solution in order to warm it, the soap film at the other end will form a bubble. Received February 20, 1923
Calendar of Meetings International Photographic Arts and Crafts Exhibition-Grand Central Palace, New York City, April 21 t o 28, 1923. American Oil Chemists’ Society-14th Annual Meeting, Hot Springs, Ark., April 30 and May 1, 1923. American Electrochemical Society43rd Semiannual Meeting, New York City, May 3 to 5, 1923. American Association of Cereal Chemists-9th Annual Convention, Sherman Hotel, Chicago, Ill., June 4 to 9, 1923. American Leather Chemists’ Association-20th Annual Meeting, White Sulphur Springs, W. Va., June 7 to 9, 1923. American Institute of Chemical Engineers-Summer Meeting, Wilmington, Del., June 20 to 23, 1923. American Society for Testing Materials-26th Annual Meeting,? Atlantic City, N. J., week of June 25, 1923.
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