T H E J O I * K S . I L O F I L V D C S T R I A L A.VD E-VGIiVEERING C H E M I S T R Y
j82
T h e curve f o r surface tension is decidedly irregular b u t shows a tendency t o slope upwards. This indicates t h a t among petroleum hydrocarbons surface tension varies in t h e same direction as specific gravity. This constant is, however, so strongly affected by small variations i n chemical composition t h a t it is a t present of little value as a means of identification. I t is hoped, however, t h a t later these irregularities m a y be understood well enough t o furnish scientific as well as, useful industrial information. Capillary constant curves show t h e same irregularities as those of surface tension b u t lack t h e slope upward. This is to be expected when t h e method of derivation of t h i s constant is considered. I n considering t h e molecular-weight ” graph, i t appears t h a t t h e agreement of this constant with C O N S T A N T S OF “ N A P H T H A ” A N D “KEROSENE“ CUTS OF Or1.S STUDIED UP TO 150° C. KEROSENE-B. P. 150’ T o 300’
T A B L E \‘-PHYSICAL
NAPHTHA-B. P. Sample Sp. Refr. Surf. Cap. No. gr. index tens. const. 815 764 816 13.16
765 269
0 706 0.716 0.722 0 726 0.731 0.733
1.392 1.398 1 400 1.402 1.405 1.406
19.96 20.54 20.02 20.52 19.34 21.12
5 82 5.88 5.69 5.79 5.57 5.97
Heald 0 . 7 3 4 1 . 4 0 6 2 0 . 3 8 5 . 6 9 1339
0 , 7 3 6 1.407 1 9 . 4 1 5 . 4 1
1280 S. M . 273 R . hi.
0.741 0,744 0.750 0.765
1.410 1.410 1.412 1.418
20.28 21.34 20.74 22.37
5.61 5.87 5.6i 5.99
Sample Sp. No gr. 815 76 4 816 765 13.36 1281 1339 1280 269
Heald R. R . R . M.
273 S. M.
Mex. Kern 59 I
0.789 0.790 0.292 0.195 0.808 0.811 0.814 0.815 0.820 0.824 0.836 0.841 0.842 0.849 0.861 0,878 0.878
Refr. Surf. Cap. index tens. const 1 ,437 1.438 1.439 1 ,440 1 ,445 1.448 1 ,449 1.451 1.452 1.454 1.458 1.459 1.463 1.466 1.475 1,476 1.476
24 73 25.07 23.96 24,66 2 5 . 59 26.80 23.91 25.04 23.18 25.27 26.34 26.57 25.50 26.40 26.96 27.79 26.87
6.44 6.50 6.20 6.43 6.49 6.66 6.02 6.30 5.77 6.28 6.45 6.46 6.20 6.37 6.40 6.48 6.26
specific gravity, though theoretically t o be expected, is conspicuous b y its absence. N o satisfactory explanation appears except t h a t there is some inherent error i n t h e method here employed for t h e determination of molecular weights. Present experience indicates t h a t t h e measurement of this constant b y t h e cryoscopic method with benzol as a solvent is of doubtful value i n t h e identification of petroleum distillates. T h e experimental values are recorded with a full knowledge of their being (‘so-called A\Iolecular Weights.” COXCLUSIONS
I-The present series of experiments has tended t o , justify t h e methods of identification (distillation, specific gravity a n d refractive index) usually employed in petroleum testing laboratories. 11-Volatility a n d specific gravity are t h e t w o most important constants a n d a knowledge of these two is generally sufficient for t h e identification of a n oil. 111-Refractive indices v a r y in t h e same direction as specific gravities. W h e n only small quantities of distillates a r e available, determinations of t h e former are more convenient t h a n measurements of specific gravities. IV-Surface tension is a constant not yet of value. T h i s is o n account of o u r lack of knowledge regarding variations caused b y t h e probable presence of small quantities of certain substances in crude petroleums. Surface tensions in general seem t o increase with specific g r a v i t y when relations among petroleum hydrocarbons a r e considered.
YO]. 7 , NO. 7
V---Cryoscopic ‘ I molecular weights,” as measured b y t h e cryoscopic method with benzene as a solvent. are of questionable value in t h e s t u d y of mixtures of petroleum products. T h e experimental work connected with t h e determinations reported in this paper was carried o u t in t h e laboratories of t h e Departments of Physical Chemistry a n d Industrial Chemistry of Columbia L‘niversity, New York. CHEMICAL SECTION OF PETROLfiUM DIVISION L,. BUREAU O F MINES, PITTSBURGH
s.
THE SPECIFICATION OF VULCANIZED RUBBER GUM BY VOLUME AND ITS DETERMINATION BY A NEW SOLUTION METHOD By FRANK GoTTscH Received April 21, 1915
T h e following methods for t h e chemical analysis
of rubber goads are those in use at M t . Prospect Laboratory, D e p a r t m e n t of Tf7ater Supply, Gas a n d Electricity, C i t y of Xew York. These methods cont a i n certain m a t t e r original with t h e a u t h o r , under FILLERS,” “FOREIGX t h e headings of “ M I X E R A L POTASH EXTRACT,” “VULCANIZED RUBALCOHOLIC BER G C M BY WEIGHT,” and “VULCANIZED RUBBER G U M BY VOLUME.’’ T h e method for “ F R E E S U L F U R ” is novel in t h e application of a well-known method for total sulfur t o t h e free sulfur determination. METHODS O F TEST
SAMPLES-Samples shall be taken representative of the lots to be tested. BLANKS-Blanks shall be run and deductions made according to the lots of reagents caeces-In the event of any determination not falling within the limits given in the specifications, a check test shall be made before the report is sent out PREPARATION OF SOFT RUBBER-Prepare a sample of not less than 25 grams, taking pieces from various parts of the original sample. The backing of fire hose shall be buffed off before grinding; in all other hose, separate samples of tube and cover shall be made, without removing the backing or friction compound. Other rubber goods built up with friction fabric shall have the rubber layers ground up without removal of the adhering rubber friction. GluNDING-The sample shall be cut into small pieces and then run through the grinder, taking for analysis only such material as will pass a standard 20 mesh sieve. Care must be taken to see that the grinder does not become appreciably warm during the grinding. If the nature of the material is such that i t gums together so that it will not pass through the sieve, as would be the case with undervulcanized samples, i t will be sufficient to pass the material through the grinder twice and accept all the material for the final sample. Crude rubber shall be cut with scissors. Pass a strong magnet through the sample to remove any metal from the grinders, mix thoroughly, and put in tightly stoppered bottles. Do not expose to sunlight or heat. HARD RUBBER-Samples of this material shall be prepared for analysis by rasping REAGENTS-Acetone shall be distilled not more than I O days before use over anhydrous potassium carbonate, using the fraction 56 to 5 7 ’ c . ALco!kolic polash shall be of normal strength, made by dissolving the required amount of potassium hydroxide in absolute
J u l y . 191j
T H E J O U R N A L OF I N D C S T R I A L d S D ENGILVEERIJG C H E M I S T R Y
alcohol the day before use, and allowing to settle. Only the clear solution shall be used. B a r i u m chloride solution shall be made by dissolving roo grams of barium chloride in one liter of distilled water, and adding two or three drops of concentrated hydrochloric acid. If there is any insoluble matter or cloudiness, the solution shall be heated on the steam bath oyer night, and filtered through S. & S. 589 blue-ribbon filter paper. Tzrrpentine shall be redistilled. ,412 reegeizts shall be of C. P. quality
583
cent solution of soluble cotton in amyl acetate into the united warm liquids in the zoo cc. beaker, cool and add redistilled turpentine until a good “flock” has formed, adding a t least 75 cc. of turpentine with constant stirring. Allow the liquid to stand until the flock has settled. The supernatant liquid is decanted and filtered by suction through an alundum crucible (Sorton R. A . 84-B. P. 5204) placed in the Spencer holder (E. 8r A . 1913, No. 2384). Wash the flock by decantation with turpentine, filtering the latter, transfer the whole to the crucible, then dissolve carefully in a few cc. of acetone, and wash the fillers with acetone, being careful not to allow the fillers to cover A s A L Y SI s up the sides of the crucible and so cause clogging. Wash thorACETOXE EXTRACT-Place a two gram sample, which has oughly all beakers and crucible with acetone, using an acetone been ground not more than 24 hours before, in an acetoneexextracted policeman. Dry to constant weight a t 105 to I 10’ C., tracted paper thimble, and insert in a glass syphon cup (E. & A. cooling in a desiccator. Evaporate all the filtrates and wash1913, No. 2846) under a condenser (E. & A. 1913, No. 2848). ings, transfer to a weighed porce!ain dish, burn off the organic Dry and weigh, by means of a wire loop, a clean 8 in. X I I / ~ in. matter, cool in a desiccator and weigh. Add this weight found test tube weighing between zo and 40 grams, pour in j o cc. ace- to the fillers in the crucible, and calculate and record as “mintone, connect the apparatus, and extract continuously for 7 eral fillers.” hours in such a manner that the drops of condensed solvent fall TOTAL SuLFvR-Mix a five-tenths ( 0 . 5 ) gram sample with directly on to the ground rubber, and the syphon cup fills be- six (6) grams of potassium carbonate and four (4) grams of tween zl/, and 3l, 2 minutes, that the discharge of the syphon sodium peroxide and proceed exactly as under “free sulfur.” cup does not appreciably interrupt the boiling, that the condensed Calculate the results in the same manner and record as “total solvent filters rapidly through the paper thimble, and that no sulfur.” fine particles of rubber or fillers are carried over. If the soluFOREIGN ALCOHOLIC POTASH EXTRACT-\vhen the presence tion in the cup is colored after seven hours’ extraction, the ex- of tar, pitch or asphalt is not indicated, spread out the rubber traction shall be continued for four hours the next day. Evap- residue from the acetone extraction and dry in the water oven orate off the acetone from the tube in a slanting position over a t 95 ’ to roo” C., until the odor of acetone is no longer apparent. livc steam, wipe off the outside with a clean linen cloth, and dry Transfer to a IOO cc. pressure flask (E. & A . 1913, No. 1064), to constant weight in the water oven a t 95 to 100’ C., or until fitted with washers previously extracted with alcoholic potash. the weight increases, cooling in a desiccator. Calculate and Add 50 cc. of alcoholic potash, stopper and heat in an air oven record as “total acetone extract.” kept between 105 O and I roo C. for four hours. Cool the flask, FREE svLFvR-Entirely transfer the residue from the tube filter and wash the residue with hot absolute alcohol until the to a 60 cc. iron or nickel crucible (E. & A. 1913, No. 2366) by washings are no longer colored. Make the filtrate strongly acetone, chloroform, or benzol, evaporate off the solvents on acid with concentrated hydrochloric acid to precipitate potasthe steam bath and add six grams of potassium carbonate and sium chloride, allow to settle, filter and wash with hot chlorofour grams of sodium peroxide. Mix by rotating the crucible, form into a small casserole. Place the casserole on the steam cover, heat a t a low temperature over an asbestos shield to avoid bath and evaporate until the odor of hydrochloric acid just sulfui- fumes, until the mixture fuses, then bring to quiet fusion disappears. Take up the residue with chloroform, filter and for 15 to 20 minutes. Avoid rapid heating and explosions. wash with hot chloroform into a beaker, evaporate the chloroRotate the melt while solidifying. When cool, put the crucible form and examine the residue. If the residue is not oily or and cover into a casserole containing z o o cc. of water, add 5 to greasy to the touch, no report shall be made. If the residue is I O cc. of bromine water. and boil until the melt is dissolved. oily or greasy to the touch, it shall be washed with small por.Wow to settle, decant, filter and wash through a thick filter tions of warm 88’ Beaumk naphtha, filtered through a washed with hot water. Cool, acidify the filtrate with dilute hydroplug of cotton into a small weighed beaker, the naphtha evapchloric acid, using Congo red paper, make up the volume to orated, and the beaker dried in the water oven a t 95 to 100’ C. 400 cc., and precipitate boiling with I O cc. of a I O per cent in 15-minute periods until the weight is constant, or increases, solution of barium chloride, keeping the beaker covered with cooling in a desiccator. Calculate and record as “Foreign a watch glass. Allow the precipitate to stand over night, filAlcoholic Potash Extract.” ter on an asbestos mat in a Gooch crucible, wash with hot water, FOREIGN CHLOROFORM EXTRACT-If the compound is light ignite and weigh, cooling in a desiccator. Calculate to sulfur in color, tar, pitch and asphalt shall be considered absent. If (factor 0 . 1372), and record as “Tree sulfur.” the compound is dark or black in color the residue after the ORGANIC ACETONE EXTRACT-When Waxy hydrocarbons acetone extract determination above, without removing the are not to be determined, subtract the percentage of free sulfur acetone, and before the alcoholic potash extraction is made, is extracted with chloroform for four hours in the same manner from the percentage of total acetone extract above, and record and by the same procedure as for the acetone extraction. If the difference as “organic acetone extract.” XINERAL FILLERS-Extract a one gram sample as under the chloroform extract is very dark in color, or the residue is “acetone extract” above for 4 hours and dry the rubber in the tarry, from its calculated amount shall be subtracted 3 per cent water oven a t 95 to roo’ C. until the odor of acetone is gone. of the weight of vulcanized rubber gum as determined below, Transfer the sample to a IOO cc. beaker, burn the thimble to and the balance recorded as “Foreign Chloroform Extract.” PRECAUTIONS-when the chloroform extraction is made the ash, and add the residue to the beaker. Add 50 cc. of clear molten salol, and heat the beaker on the hot plate a t a tem- day after the acetone extraction, the rubber residue shall be perature of not less than 1 2 0 ’ nor more than 150’ C., stirring covered with acetone over night. When the alcoholic potash extraction is made the day after either the acetone extraction occasionally until the rubber is apparently dissolved. After settling a few minutes, carefully transfer the liquid to a z o o cc. or the chloroform extraction, the dried rubber residue shall beaker and examine the residue in the bottom of the smaller be covered with the alcoholic potash over night. beaker for particles of undissolved rubber. If found, more CARBONACEOUS FOREIGN MATTER-Heat about a one gram salol is added and solution completed. Stir two cc. of a I per sample with 30 cc. of concentrated nitric acid and 15 cc. water.
586
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
is b e t t e r t o specify t h e a m o u n t of t h e original m a terials. T h e experience of t w o years h a s s h o w n proper correspondence of analysis t o ingredients used, t a k i n g i n t o account changes produced b y process of m a n u f a c t u r e a n d vulcanization, when a d u l t e r a n t s h a v e n o t been introduced. T h e m a n u f a c t u r e r c a n n o t t a k e chances with materials of u n k n o w n composition under our methods. I n specifications reading “ I t shall c o n t a i n , ” t h e best evidence t h a t certain materials h a v e been used i n t h e c o m p o u n d is t o have a n inspector a t t h e factory t o see t h e m p u t in. We t h i n k we are safe i n saying t h a t rubber manufacturers h a v e h a d e n o u g h of t h i s system. We believe t h a t “ I t shall show” should be specified, t h a t t h e m e t h o d s of analysis a n d t e s t s should be s t a n d a r d i z e d a n d t h e specific items defined. T h i s seems b y f a r t h e b e t t e r m e t h o d a n d offers fewer opportunities for disputes. SPECIFICATIOX
OF
VULCANIZED
RUBBER
GUbI
BY
voLuME-The physical properties of a rubber comp o u n d a n d t h e quality are more properly related t o t h e percentage by volume of vulcanized rubber g u m prese n t t h a n t o t h e percentage b y weight. T h e large m a j o r i t y of rubber goods are sold b y bulk a n d used b y b u l k r a t h e r t h a n b y weight. This volume conception is necessary t o a n understanding of rubber mixings. Now t h e specific g r a v i t y of t h i s vulcanized r u b b e r g u m (resin-, ash-, a n d air-free) is very nearly u n i t y . T h e specific gravity of t h e purest washed a n d dried r a w r u b b e r is g r e a t l y influenced b y t h e mode of prepa r a t i o n i n regard t o m i n u t e air bubbles enclosed in t h e r u b b e r , a n d varies f r o m 0 . 9 0 t o 0 . 9 j . According t o Philip E . Y o u n g , inventor of Y o u n g ’ s G r a v i t o m e t e r , t h e best value for t h e pure air-free r u b b e r g u m is 0 . 9 8 . W i t h 30 per cent of combined sulfur without mineral fillers, t h e specific g r a v i t y of t h e vulcanized rubber g u m h a s been shown t o be I . 00 T h e variation in t h e specific g r a v i t y for various degrees of vulcanization is in a n y case a small one a n d for purposes of calculation t h e specific g r a v i t y of all vulcanized rubber g u m m a y be t a k e n as u n i t y . B y multiplying t h e percentage b y weight of vulcanized rubber g u m present b y t h e specific gravity of t h e c o m p o u n d a product is o b t a i n e d which represents t h e percentage b y volume of vulcanized rubber g u m present. T h i s v o l u m e would be strictly correct if divided b y t h e t r u e specific g r a v i t y of t h e vulcanized rubber g u m present. However, i t is n o t intended t o determine t h e t r u e volume, b u t a factor obtained as specified. i2s t h i s is very nearly t h e t r u e volume of vulcanized rubber g u m present i t h a s been so called in t h e methods. Y o closer m e t h o d for determining t h e t r u e volume is possible, or necessary. I t will a t once be seen t h a t h a r d r u b b e r s will show more vulcanized rubber g u m b y weight t h a n t h e original r u b b e r p u t i n ; a n d t h a t for soft rubber of good quality t h a t which is t a k e n a w a y a n d reported a s organic acetone extract will a b o u t equalize t h e combined sulfur. T h e m i n i m u m vulcanized rubber g u m b y volume
Vol. i 3S o . 7
t h a t will give a sound article can h a r d l y be less t h a n j j per cent if m a d e up of r u b b e r , sulfur a n d mineral fillers only. Less t h a n t h i s a m o u n t needs something t o fill t h e pores between t h e particles of fillers in t h e way of resins, oils, waxes or a s p h a l t u m . As t h e percentage of vulcanized rubber g u m b y volume decreases in a c o m p o u n d m a d e up of r u b b e r , sulfur and mineral fillers only. t h e liability of decay b y oxidation due t o porosity becomes greater. E v e r y manufacturer knows t h a t with a fixed percentage b y weight of rubber p u t i n t o a compound a n d m a d e i n t o a n article with fixed dimensions, like a hose t u b e or valve, t h e lighter h e c a n m a k e t h e specific g r a v i t y , t h e more m o n e y he saves. T h i s is due t o a reduction in t h e volume of rubber present By specifying a m i n i m u m percentage b y volume of v u l canized rubber g u m t h e choice of fillers is left entirely t o t h e m a n u f a c t u r e r , as i t should be. W h e t h e r he uses light or h e a v y fillers is immaterial as long as t h e volume specified is o b t a i n e d , a n d t h e chemical and physical requirements are met. F o r example, let us suppose a m i n i m u m of 7 5 per cent of vulcanized r u h ber g u m b y volume is specified. T h e manufacturer can m e e t t h i s b y a c o m p o u n d with a specific gravity of I . 2 2 showing 6 1 . j per cent vulcanized rubber g u m b y weight or b y a c o m p o u n d with a specific gravity of 2 . 2 j showing 33. o per cent vulcanized rubber g u m b y weight, or b y various combinations between these extremes. T h e s a m e result can be obtained b y fixing a m i n i m u m specific g r a v i t y a n d a m i n i m u m percentage b y weight of vulcanized r u b b e r g u m present b u t t h e kind of fillers would t h e n be limited t o a few or a mixture of a few having a certain density. T h e m e t h o d specified permits a n y manufacturer t o m a k e as good a c o m p o u n d as he knows how, using good rubber a n d a n y fillers he t h i n k s best. H e will be on a n equal basis of competition with a n y other manufacturer as f a r as t h e quality of t h e finished a r t i cle is concerned. H e m u s t necessarily also deliver a n equal weight of vulcanized r u b b e r g u m of quality required t o meet t h e physical tests. I n t h e few cases where i t is advisable to specify t o t a l sulfur i t is n o e x t r a hardship for t h e manufact u r e r t o specify t o t a l sulfur in all forms. I t is impracticable t o determine sulfur present a s barium sulfate, when other forms of b a r i u m are present. Xs a rule, t h e other chemical a n d physical t e s t s , including a n ageing t e s t , can be m a d e a d e q u a t e a n d sufficient t o ensure t h e delivery of goods m a d e up from ne\T r u b ber. T h e a m o u n t s of sulfur a n d organic acetone extract are specified as percentages of t h e weight of vulcanized rubber g u m present as t h e y are functions of t h e a m o u n t of rubber present. T h e specification of fixed limits for these as percentages of t h e c o m p o u n d does n o t m a k e d u e allowance for such corresponding variation of these constituents mith t h e a m o u n t of rubber used. T h e quality of t h e rubber used as well as t h e suitability of t h e fillers a n d t h e proper vulcanization are fixed b y physical t e s t s which will be described in a n a r t i cle t o follow. MT. PROSPECT LABORATORY, BROOXLYN, h7EW Y O R K
