February, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
before going into service and tested on the flexing machine flexed 2150 times (average) before failure. With no change other than increasing the flexing life of the cords in this type of tire to 3430 flexes, there resulted an increase in mileage of approximately 50 per cent.
301
Such a result would indicate that the increase in mileage is proportional to the increase in flexing life. That this is not consistently the case has been found in further teats. However, the results are such as to indicate that the flexing test is of distinct value in the study of cord tire fabrics.
Specific Gravity of Paraffin Wax' By F. J. Morris a n d L. R. Adkins T 7 a c u u ~OILCo., ROCHESTER, N. Y.
HE determination of specific gravity of paraffin waxes
T
seems to be a rather neglected subject. The investigator in pure science has not been interested, probably because commercial waxes are mixtures of several, principally paraffin, hydrocarbons, hard to separate. I n the refinery, wax is usually weighed, being sold by weight, and a knowledge of the specific gravity is not essential. Chemical Abstracts for fifteen years back gives no reference to this constant. The coefficient of expansion a t 20" C. of the Smithsonian Tables2 and the statement in Redwood3 that the specific gravity a t 60" F. is about 0.908, and a t 212" F. 0.750 are the only data the writers were able to find. D e t e c t i o n of Air in Paraffin Wax
Commercial paraffin wax contains a variable amount of air.
If a piece of hard u'ax is broken, the craters of disrupted air bells appear on the broken surfaces. Besides these visible bells, there are smaller ones which can be seen only with a glass. The approximate amount of air in the samples examined was not determined, but the fact that i t is air and not hydrocarbon gas was determined by a rather crude method. A 2-liter Pyrex boiling flask was nearly filled with wax and cooled. When the wax was nearly set, the neck of the flask was drawn out to a capillary and the flask rapidly exhausted t o less than 2 mm. pressure. The capillary was sealed off and the flask allowed t o remain a t a temperature of 150" F. (65.6" C). for 15 hours. On breaking the neck under water and analyzing the remaining gas in the flask with an Orsat, it was found to contain 20 per cent oxygen. It was therefore assumed t h a t the gas was actually air.
Specific gravity4
=
w. - ( W + SI1 + 7' "
s 1
where W , = weight of object in air; SI= weight of sinker in S)l = weight of object plus sinker immersed in water; (W water.
+
The usual form of wide-mouth pycnometer, which is commonly used for tarry materials, failed because the wax as it solidifies pulls away from the sides, leaving air spaces. Water added afterwards for the second weighing does not entirely fill these spaces. By using alcohol instead of water and putting it in as soon as the wax begins to set, these voids are filled. But alcohol has a slight solvent action on wax and some wax was lost thereby. A modified Nicholson hydrometer, after a few trials, solved the problem. The ordinary Nicholson consists of a float carrying a pan on a slender stem above water and another pan hung from a hook below water. Specific gravity is determined by balancing the sample in air and in water with the addition of weights and calculating the results from the difference in weights used. As the usual metal Nicholson has some edges which hold air bells, and as waxes begin to soften and separate drops of low melting point constituents much below their official melting point, a special glass hydrometer was designed. The pan in the liquid is made of two small 0.920
0.900
The occluded air is apparently not held in solution when a 0.880 wax is melted a t atmospheric- pressure. Samples held in ,X vacuum for several hours at 130" F. (54.4"C.) and the specific 'z gravity taken quickly in air gave the same figures as a similar $o.860 sample melted in air and the specific gravity taken in air a t $ that temperature. Until i t was realized that air was always go,84o present in variable amount in solid wax, attempts to determine specific gravity by any method were disappointing. Results on different portions of the same samples did not check. The 0.820 method or some little detail in the manipulation were always blamed. 0.800
Procedure
The ordinary method of determining specific gravity of solid water-insoluble substances by weighing in and out of water a t 60" F. (15.56" C.)-in this case, of course, with a weight tied to the'wa,x when weighed in air-even with an airfree sample, is hard t o manage. 1 Received August :31, 1926. Presented before t h e Division of Petroleum Chemistry a t the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1926. 2 Smithsonian Physical Tables, p. 219 (1921). 8 "A Treatise on Petroleum," p. 256.
I
I
60° F.
80' F. 26.7' C.
15,50c.
Figure 1-Specific
I looo F.
1 12O0F. 48.90 c.
\
1 -OF.
37 8 O C. 04 4 o c . Temperature Gravity of Waxes a t 60' t o 130° F.
crystallizing dishes set up something like a The inner one, inverted, has two V notches in the edge to allow a free flow of water in and out. h'o melted wax can get out as i t floats to the top of this inner dish, Calculated from formula in Ferry "Physics Measurements," p. 47
(1918).
INDUSTRIAL AND ENGIiVEERING CHEMISTRY
302
Samples for test were placed under 30 mm. or less pressure for 24 hours a t 140" to 150" F. (60" to 65.6" C.) and cooled a t room temperature in the same vacuum. The characteristic whiteness of refined wax disappears with this treatment. Airfree samples are of a blue-gray color and somewhat translucent. After this treatment carefully cut samples were weighed on the Nicholson in air at 60" F. (15.56" C.), then placed in the lower pan and weighed in water a t the same temperature. Results
Table I shows specific gravities a t 60" F. of several semirefined waxes. The last sample is from a tar still stock. The next to the last column gives the specific gravity a t 130" F. The last column gives the value at 60" F., which would be ordinarily determined from the apparent specific gravity a t 130" F. and the usual petroleum conversion table.5 Table I-Specific ~
Gravity of Semirefined Waxes
NICHOLSON A T 60 F.
AT 60" F6 130
SPINDLE
HYDROM-F.
MELTING POINT
AND P E TROLEUM CONVER-
F,
Average
Checks
SION
TABLE
I
a
F.
O
103
c.
39.4
109 42.8 115.1 4 6 . 2 1 1 8 . 5 48 123.2 50.7 127.2 52.9
l
I 0.8799 0.8797 0.8805 0.8804 O.SS$0.8844 0.8955 0.8973 0.9057 0.9048 0.9045 0.9056 0.907 0.9067 0,925 0.915
I
0.0008 0.8801
0.778
0.8053
0 , 0 0 0 4 0.8842 0.0018 0.8964 0.0011 0.9053
0.777 0.780
0,8044 0.8072
0.0003 0.01
0,784
0.811
0.9068 0,920
0.782
...
0.8091
...
I n an attempt to determine where the break comes in the expansion coefficient, the specific gravities of several waxes 6
Bur. Standards, Circ. 07.
VOl. 19, Yo. 2
were taken with the Kicholson every 10" F. (5.56" C . ) from 60" to 110" F. (15.56" to 43.3" C.) and every 5" F. (2.8" C.) from 110" to 130" F. (43.3" to 54.4" C.), compared with water at 60" F. Table 11-Specific
Gravity of Three Paraffin Waxes from 60° to 130° F. Melting Point
TEJIPERATVRE
F. 60 70 80 90 100 110 115 120 125 130
0
118.5' F. (48' C . )
123.2' F. (50.7' C.)
127.2' F. (52.9" C . )
0.906 0.899 0.885 0.882 0.874 0.858 0.841 0,801 0.802 0.780
0.907 0.903 0.890
0.920 0.913 0.905 0.893
c.
15.56 21.1 26.7 32.2 37.8 43.3 46.1 48.9 :1.7 a4.4
0,887
0.868 0.856 0.830 0.802 0.801
0.785
0.878 0.876 0,870
0.848 0.818 0.803
The results, shown in Table 11, are the average of two or three determinations, none varying more than 0.005. Probably the complex nature of the material had something to do with the slight discrepancies. This is shown better graphically in Figure 1. The 118.5" F. (48" C.) melting point sample is representative of wax made from neutral wax distillate; the 127.2" F. (52.9" C.) melting point sample from tar wax distillate. I n the 118.5" F. (48" C.) wax there is a break between the 100" F. (37.8" C.) and 120" F. (48.9" C.) where probably most of the hydrocarbons composing this sample melt. The significance of the flat spot between 120" F. (48.9" C.) and 130" F. has not been determined. It occurred in every wax of this nature examined. There is a flat spot 20" to 30" F. (11.1" to 16.7" C.) below the melting point on each wax, which of course is not accounted for. Incidentally, the Nicholson, checked on one was a t 130" F. with an ordinary spindle hydrometer and with a pycnometer, gave the same figure within a reasonable error.
Effect of Moisture on Electrical Properties of Insulating Waxes, Resins, and Bitumens' By James A. Lee and Homer H. Lowry BELLTELZPXONB LABORATORIES, INC.. NEW YORP,N. Y.
T
HAT most materials absorb water from an atmosphere containing water vapor has been generally recognized for many years. Further, the occasional lack of agreement between the results of electrical measurements on insulating materials made by different investigators, as well as the wide range of electrical values sometimes assigned to a given material by any one investigator, has been attributed to an undetermined effect of the water content of the material. However, there are few records of systematic efforts to relate the electrical properties of insulating materials definitely to their water content. Evershed2 has published an elaborate investigation of the effect of moisture on the volume resistivity of very porous materials, such as paper and cloth. Similarly, A. Schwaiger3 studied the rate of decrease of insulation resistance of unimpregnated paper when exposed to high humidity. cur ti^,^ in a comprehensive study of the "Insulating Properties of Solid Dielectrics," includes a brief account of the effect on volume resistivity of drying a number of materials, including f
Received September 21, 1926.
* J . Inst. Elec. Eng. (London), 2,
51 (1914). :Arch. Elektrofech., 3, 332 (1915). 4 Bur. Standards, Bull. 11, 359 (1914-1915).
.
Bakelite, marble, slate, shellac, and several molding compounds. More recently, Kujirai and collaborators5 have published work on the effect of humidity on the insulation resistances of fibrous materials. showing that the change in resistance could be quantitatively related to change in humidity. It may be observed that the investigations cited above have been very largely limited to fibrous materials. I n order to obtain similar information about the various waxes. resins, and bitumens which are used for insulating purposes. the work reported in this paper was undertaken. The scope of the work was broadened, however, so as to include not only a study of the relation of insulation resistance, or volume resistivity, to the moisture content of the materials, but also to include a similar relation for the dielectric constant and the effective conductivity a t 1000 cycles. A list of the materials studied is given in Table I, together with their grade, source, and physical constants. Attention has been directed to a comparison of the insulating properties of a large variety of materials when initially free from moisture and at intervals after immersion in 3.5 per cent sodium chloride solution, which is equivalent to exposiire to 9 s per cent relative humidity, except for the Sci. Papers Inst. Phys. Chem. Research ( T o k y o ) , 1, 79 (1923).
