January 15, 1929
INDUSTRIAL AND ENGINEERING CHEMISTRY
A
4 cm. below the barometer reading, b e c a u s e , of dissolved air, vapors, etc. T h e constant height is taken as the zero reading. A few cubic centimeters of the volatile liquid are then poured into the funnel, which is stopped loosely to avoid excessive evaporation. The funnel is lowered again with the I I stopcockopen, and then shut off with volatile liquid on both sides of the stopcock. Again the funnel is raised and the new height of mercury (a) read as before. The difference
I I I ii
39
in height gives the vapor pressure of the liquid a t the surrounding temperature. The correction for height of the liquid column (a-b) is within experimental error. For other temperatures a jacket of warm water or steam, etc., around the whole stem of the funnel must be provided. With impure liquids, such as gasoline, the observed vapor pressure as determined by any method varies greatly according to the volume of the vapor space, far more than the abovementioned error due to air dissolved in the mercury, so that it is useless to eliminate the latter completely. For comparison of gasolines the ratio of vapor to liquid volumes must be set arbitrarily, and this adjustment is particularly convenient with this apparatus. The ratio might be 1:9, corresponding to a tank 90 per cent full. For fairly pure liquids, such as commercial acetone, ether, etc., a much higher ratio, five, to ten times the liquid volume, would be preferable. Results agreeing well with literature values have been obtained for ether, acetone, benzene, carbon tetrachloride, chloroform, and pentane. The time for a test is 5 to 10 minutes; for check determinations, less than 1 minute.
Rapid Determination of Specific Gravity of Semi-Solid Bituminous Substances' S. E. Berkenblit BOARDOF TRANSPORTATION OF THE CITY OB NEW YORK,49 LAFAYETTE ST., NEWYORE,N. Y.
HE specific gravity of semi-solid bituminous substances is usually determined by means of a wide-mouth pycnometer or by the Sommer hydrometer. I n either case the solidified material has t o be removed after each determination, so that the cup holding the sample may be cleaned and made ready for the nest test. The cleaning of the apparatus usually consumes more time than the actual determination and causes considerable sloppiness. Moreover, the delicate glass pycnometers very often , break during cIeaning, and with the Sommer hydrometer difficulties are frequently encountered in the removal of the cover and flange from the metal cylinder, as a result of which the cylinder gets scratched or indented. The writer has developed a sho;t method eliminating the cleaning of the pycnometer and requiring only one weighing. This method has been used for over three years in this laboratory for determining the specific gravities of asphalts employed for waterproofing purposes in the subways and ranging in melting point from 125" to 175" F. (51.7" to 79.4" C.) (ball and ring), and has been found to give very satisfactory results. Duplicate analyses made on the same material have been found to check within 0.002. The method can be used to advantage in connection with all kinds of solid and semisolid materials. A detailed description of the method and the apparatus required is given below. I n the method described the specific gravity is obtained at 77" F. (25" C.), which is the temperature specified in the A. s.T. M. Standard Method of Test for Specific Gravity of Asphalts and Tar Pitches, Serial Designation D71-27.
T
Description of Apparatus
BRASSMom-This consists of a brass tube, 13/4 inches (4.4 cm.) high and ls/16 inches (3.3 cm.) in diameter, open at 1
Received October 30, 1928.
both ends and cut longitudinally in two equal parts, which are held together with a rubber band. The mold can hold about 40 grams of asphalt or pitch. It is placed on an amalgamated brass plate and the molten sample poured into it. GLASSCYLINDER-This cylinder is 8'/2 inches (21.6 cm.) high and 13/4 inches (4.4 cm.) in diameter, open a t the top. At the bottom a three-hole rubber stopper is inserted, from which one connection is made to a 500-cc. separatory funnel, serving as a leveling bottle. Another connection leads to a 50-cc. buret, the lower end of which has been cut off below the zero mark. Both the buret and the leveling bottle are held a t the desired height by means of an iron support. Into t h e t h i r d hole of the rubber E stopper is inserted a glass tube, '/4 inch (6 mm.) inside diameter, leading to the outside of the c y l i n d e r , parallel to its side. M This glass tube has a mark etched on it, 5 inches (12.7 cm.) from the lower end. The glass cylinder with the side-tube attachment may be clamped in another iron support. This apparatus is not expensive and can be constructed in any laboratory. Preparation of Sample
The sample of the bituminous substance is melted in a tin can at the lowest possible tepperature and poured into the brass mold to fill it slightly more than
, , ~ ~ ~ ~ ~ ~ ~ " Bituminous Substances
ANALYTICAL EDITION
40
full. The inside of the mold is covered with a thin film of glycerol to prevent the bitumen from sticking. The mold with the sample is first cooled in air, then immersed for 30 minutes in water maintained a t 77" F. (25" C.). The excess material extending above the level of the mold is then cut off with a hot knife. Method of Determination
The sample is removed from the mold and rinsed in water kept a t 77" F. (25" C.) to wash off the glycerol. It is then wiped with absorbent cotton t o remove all the water from the surface, and weighed on the balance. The weighing should be done quickly or the asphalt will stick to the watch glass. Fill the leveling bottle, L, with water at 77" F. (25" C.) and open stopcocks B, C, and D to connect the cylinder A with the leveling bottle and with buret E. Fill both the buret and the cylinder with water until the mark M on the side tube is reached. Adjust the level a t M very carefully, then close stopcock B to discontinue the flow of water and take the reading on the buret,. Suspend the weighed sample of asphalt or pitch by means of a silk thread and immerse in the water in the cylinder A. The asphalt will displace some of the water, causing the water levels in the cylinder and in the buret to rise. Now lower the buret slowly until the water level in the cylinder A is brought back to the starting point, corresponding to mark M on the indicating tube. Take the second reading on the buret. The difference between the first and second readings is equivalent to the volume of water displaced by the sample. The density of water a t 77" F. (25" C.) being 0.997, the specific gravity of the sample is calculated from the formula:
VOl. 1, No. 1 Weight of sample
(Volume of water displaced)
x
0.997 = specific gravity
Accuracy of Method
The accuracy of this method was tested in several ways. The specific gravity of a given sample of asphalt was obtained starting from a certain reading on the buret, as described above. The same procedure was then repeated after removing the surface moisture, starting from a different point on the buret, which can be accomplished by raising or lowering the buret. A few of the results are given in Table I. Table I-Comparison of Specific Gravity Determinations Obtained by Varying Initial Reading on Buret SECOND INITIAL READWEIGHT OF READING ON ING ON WATER SPECIFIC SAMPLE SAMPLE BURET BURET DISPLACED GRAVITY
A Ai B
BI
Grams
cc.
cc.
cc.
41.0445 41.0445 40.9560 40.9560
3.60 4.20 6.80 5.00
43.40 43.95 46.10 44.36
39.80 39.75 39.30 39.36
1.0343 1.0356 1.0453 1.0437
The results obtained by this method have also been compared with those obtained by weighing a given sample first in air, then in water. (Table 11) Table 11-Com arison of Specific Gravity Results Obtained by Method Descrybed and by Method of Weighing in Air and Water WEIGHING IN SAMPLE METHOD DESCRIBEDAIR AND WATER 1 1.0360 1.0369 2 1.0600 1.0603 1.0267 3 1.0272
Acknowledgment
The writer wishes to acknowledge the valuable assistance of L. Mantell, who carried out the experimental work in connection with this paper.
Determination of Cellulose and Amount of Chlorine Consumed in Its Isolation' A Short Method Mark W. Bray U. S. FORDST PRODUCTS LABORATORY, MADISON,WIS.
INCE the various methods for the determination of cellulose in woody materials consist in the measurement of a residue obtained by some empirical procedure, a study of chlorination methods was undertaken by the Forest Products Laboratory with the view t o simplification and improvement. A procedure incorporating the best features of the several methods studied has been developed, which not only gives more accurate results with less degradation of the cellulose than obtained by previous methods, but also gives practically the same yields of cellulose regardless of the size2 of the particles chlorinated. I n addition, this method affords data showing the amount of chlorine consumed in the isolation of the cellulose. Though the Cross and Bevan3 original procedure of alternate treatments with chlorine gas and sodium sulfite solution has been modified in various ways to increase yields of a
S
1 Presented under the title "The Estimation of Cellulose in Lignocelluloses and the Amount of Chlorine Consumed in I t s Isolation" before the Division of Cellulose Chemistry a t the 75th Meeting of the American Chemical Society, St. Louis, Mo., April 16 to 19, 1928. 2 Mahood and Cable, J. IND.END.CHEM.,l a , 873 (1920). Cross and Bevan, J . Chem. Soc., 38, 666A (1880); Chem. News, 42,
*
77, 91 (1880).
less degraded cellulose, their idea is the basis of the best known methods for the isolation of the cellulosic residue from lignocelluloses and has replaced the earlier and less effective bromination m e t h ~ d . ~ Originally3 the time of chlorination was 1 hour or longer. Schorger5 shortened the time for the first chlorination to l/z hour, while Ritter and Fleck6 showed that the same quantities of lignin and substances other than cellulose are removed in a 5- to 3-minute chlorination period and that the cellulose thus isolated had undergone less degradation than that obtained as a result of the longer periods of chlorination. Prior to Ritter's work the author7 showed that prolonged chlorination degrades cellulose and therefore yields less alphacellulose, which sometimes becomes gelatinous and difficult to filter and wash. It is therefore difficult to obtain corresponding amounts of alpha-cellulose from a sample of wood cellulose prepared by the long chlorination method. However, shortening the chlorination period below that prescribed by 4
a, 27
Muller, "Die Pflanzenfaser," in Hoffmann's B e y . Entuick. chem. Ind.,
(1877). Schorger, J. IND.ENG. CHEM.,9, 566 (1917). 6 Ritter and Fleck, I b i d . , 16, 147, 947 (1924). 7 Bray and Andrews, Paper Trade J., 76, No. 8, 47 (1923). 6
