A Micro Isoteniseope OTTO F. STEINBACH and ARTHUR W. DEVOR' Adelphi College, Garden City,New York
I .
N A previous article2 the anthors described an iso-
temscope for student use which gave good results for vapor pressure measurements. Further investigation led to a modified design of the Menzies isoteniscope which could he used to d e t p i n e the vapor pressure with as little as 0.5 ml. of sample with a greater accuracy than that obtainable with the macro apparatus.
liquid in the hulb D and evacuating with a water pump. When air is admitted the sample will be forced over into the bulb B. The sample may also he removed in a similar manner by evacuating it and turning it upside down. The isoteniscope was placed in a 3-1. beaker containing the liquid used as the heating bath. This was heated to the boiling point of the liquid whose vapor pressure was to be determined. The pressure was slowly reduced in the apparatus by adjusting the leak nntil the sample began to boil and the trapped air was driven out. The pressure was then allowed to increase slowly by admitting air through the leak nntil the levels in the isoteniscope manometer were equal. The pressure and temperature were then recorded. In order to compare the experimental results with those in the literature, the log of the vapor pressure was plotted against the corrected reciprocal absolute temperature and the slope was obtained. The latent heat of vaporization, L, in calories per mole, was calculated from this slope. The results in the following table were obtained from plots on graph paper whose size was 8 X 10 inches. TABLE 1
The apparatus was blown from thin-walled 2-mm. tubing and had the approximate dimensions shown in Figure 1 which were not critical. The bulb B was placed in a plane a t right angles to that of the bulbs C and D so as to reduce the total space occupied. Before bending the apparatus, several thin lengths of solid glass rod and a few pieces of broken glass were introduced through the open end into the hulb B. This helped to promote equilibrium between the liquid and vapor phases. The isoteniscope was connected to a trap and manometer and ballast bottle, the arrangement having been described in the previous article. The apparatus may be easily filled by placing a suEcient quantity of
-
1 Present address: University of Southern California, Los Angeles, California. 1 STBINBACH, 0. F., AND A. W. DBVOR, J. CHEM. EDUC., 22,288
(1945).
L Observed
LAcu~lcd
Aniline
11,478 11 7 m ..,--"
11,270 1 1 770
0 2
Water Chlorobcnrcne Acetone Benzene
10.199 10,045 7,612 7.960
10,225 9,804 7.504 8.131
0.25 2.45 1.3 2.1
Per Cenl Error 1.85
The results are actually of a much higher degree of accuracy than shown in the table, for the accuracy depends upon the size of the graph paper selected and thus an estimated error of about 2 per cent was obtained in plotting the data. Since the vapor pressure of water a t different temperatures is known very accurately, it was felt that a real test of the data would be obtained if water were selected for the standard of comparison, and accordingly the data were plotted on much larger graph paper, 15 X 20 inches. At the higher temperatures the experimentally determined vapor pressure differed from the accepted values by about 0.25 mm. while a t the lower temperatures there was on an average 1 mm. difference. Both positive and negative deviations occurred. The anthors believe that the apparatus is capable of giving results equal to that recorded in the literature. The isoteniscope was also used to determine the boiling points of pure substances. For this purpose i t does not necessarily have to be connected to the evacu(Continued on Page 504)
A MICRO ISOTENISCOPE
(Continued from $age 496)
ating system or trap. It may also be modified by cutting i t off below the bend marked point A in the figure. The isoteniscope was wired to a thermometer and placed in a 3-1. beaker containing the heating liquid and the temperature was raised until boiling started in the bulb B. The bath was allowed to cool slowly, with vigorous stirring and when the liquid levels in the isoteniscope manometer were the same the temperature was recorded. The procedure may be repeated as often as desired and three or four determinations may easily be made by alternate beating and cooling. The boiling points readily check to within O.l°C. and the results were in good agreement with the literature values when the exposed stem and barometric pressure ccrrections were made. The micro isoteniscope also offers the possibility cf determining vapor pressures a t any desired cr predetermined temperature. The isoteniscope was mounted in a cork with a thermometer and was placed in a two-neck 500-ml. flask and connected to the trap, manzmeter, ballast bottle, and water pump as before, and the other neck of the flask was connected to a reflux condenser.
Various liquids df required dr suitable boiling points were placed in the flask or several flasks. The liquid in the flask was heated and maintained a t an even rate of boiling, the condensed vapor heating the sample to the desired temperature. The water pump was then turned on and the pressure was slowly reduced uutil boiling took place in the bulb B. After the trapped air was driven out of the isoteniscope the pressure was allowed to increase slowly until the liquid levels of the isoteniscope manometer were equal. This can be adjusted very accurately. However, the levels do not necessarily remain fixed, as slight differences in water pressure change the pressure in the system. The procedure was repeated until the pressure and temperature readings checked, since this indicated that the last trace, of trapped air had been expelled from the isoteniscope. The pressure readings checked to within 1 mm. and the temperature to within O.l°C. The results obtained were of a high degree of accuracy. The experimentally determined points fell directly upcn a large-scale plot of the accepted values log P and 1/T, within the limits of the experimental error.
0 When synthetic rayon yarns were introduced in America,'satisfactory trade acceptance depended on the development of a satisfactory sizing. Silk, which is a natural yam, is already coated with a lubricant that minimizes friction a t the weaving loom. Long experimentation finally established animal glue as the most satisfactory sizing, and today millions of pounds of glue are used for that purpose. Glue is also used as a dye leveling agent, for the preparation of water-
resistant cr splash-procf finishes, and as a sMening agent. 0 The measure cf flcw rate cf fluids is nct an unusual problem and the use cf rotameters f r this purpose is coming to be c-mmon practice. Two pamphlets on this have recently been published by the Fischer & Porter Crmpany (Hatbcro, Pennsy:vania), entitled, respective:^, "The-ry of the Rotameter," and "A New Era in Flow Rate Measurement."
