The Exudation Test for “Bleeding” in Bituminous Roofing G. L. OLIENSIS. The Barber Company, Inc., JIadison, Ill.
There is evidence that when asphalts that are incompatible in the sense aboye indicated are placed in contact with one another a t room temperatures, there will develop a t the interface between the two a very thin layer of bitumen, of a softer consistency than either, but that this film will remain permanently a t the interface until it is encouraged to migrate outward by capillarity, as when pinholes are present in the coating layer, or when a layer of dusting has been applied a t or adjacent to the interface or to the pores in the coating. This outward migration results in the scattered black spots typical of bleeding in roofing. These bleeding phenomena should not be confused with the normal exudation of very thin oily matter that occurs on the surface of all blown asphalts on aging. For example, no bleeding whatever will occur, even when a coating is of the type that develops an extremely oily surface on aging, if that coating is used with a compatible saturant. On the other hand, if the saturant is not compatible, marked bleeding can occur even when the coating is of the type that does not readily develop an oily surface on aging.
“Bleeding,” or “strike-through,” by which is meant the exudation of unsightly black spots occasionally noted on the surface of ready roofing, is due to a peculiar type of incompatibility, as yet unexplained, between the asphalt used as saturant and that used as coating. During the last 7 years the author has developed a n “exudation test” for determining this lack of compatibility between the saturant and the coating, before their use in roofing manufacture.
I
N THE manufacture of ready roofing a felted sheet is
saturated with a hot, relatively soft bituminous saturant. The excess of saturant is removed and a substantial layer of relatively hard blown asphalt coating compound is applied in a molten condition to both surfaces of the hot saturated sheet. Intimate contact between the coating and saturant is thus obtained. Granules may be applied to the upper surface of the hot coated sheet to protect the coating from actinic light and to decorate the product. The finished sheet may then be cut into shingle shapes or shipped in rolls. I n either event the layers of the finished goods are tightly packed a t a slightly elevated temperature. I n case asphalts have been used that prove incompatible in the sense just described, “bleeding,” or “strike-through,” begins to develop in the warm package, and continues steadily, not only after the product has cooled but also after application and exposure to solar heat. It is first noted as small, dull-black spots, that appear to have exuded through the minute pores, or pinholes, that frequently occur in the coating layer or a t the edges of the roofing sheet. I n time, new spots appear, while the old ones grow steadily wider and may eventually assume a glossy black color and a soft and even oily consistency. Eventually some of the spots map run together to form large black blotches all over the roofing sheet and n-ill even strike through the wrapping paper around the package. The progressive development of bleeding is shonn in Figure 1 (a, b, and e ) . Although in extreme caqes the surface of the product and the package may present a very unsightly appearance, the exudation is not particularly a p t to cause sticking in the package, as the spots appear to be less sticky than oily in cliaracter. Furthermole, after enposure for a few months during hot summer weatliei , the s l o r accumulation of duat on tht’ roof and the effect. of n eathering giatlually o h c u r e thest. black spots both on smooth and on granule-covered roofing. until they are hardly discernible. This fading of the oily spots on exposure is illustrated in Figiue 1. d shov-s thP under side of a graaule-suifaced shingle d i i c h displayed marhed bleeding after a period of exposure; e s h o w the granule-covered surface of the same shingle. On e the bleeding spots are r-isible on the upper portion which was protected by the superimposed shingle, but they have practically disappeared on the lower portion which was exposed directly to the weather.
Exudation Test The exudation test, that has been developed by the author to detect this strike-through tendency as b e t m e n any saturant and any coating, consists simply in applying a drop of the h
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C
e
FIGCRE 1. ROOFIXGS ILLUSTRATIXG PROGRESSIVE DEVELOPMENT O F BLEEDIXGI N STORAGE, .4XD EFFECTSOF EXPOWRE 199
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INDUSTRIAL AKD ENGINEERIRG CHEMISTRY
saturant to the talc-dusted surface of the coating, maintaining the latter a t a temperature of 43.33" C. (110" F.) for 72 hours, and measuring the width of the black ring of discolored talc that forms around the periphery of the spot. I n an effort to standardize the conditions of the test, the following technic has been developed: The coating is warmed t o a fluid condition. I t may then be poured into the lid of a 3-ounce (8S.7-ml.) penetration tin or other convenient receptacle in a layer 0.3 to 0.6 cm. (0.125 to 0.25 inch) thick. To remove air bubbles the surface of the coating may be momentarily heated. The surface area and total weight of the specimen are determined and the surface is then given a preliminary dusting Tvith fine roofer's talc, evenly distributed over the surface, neither the surface nor the talc being handled by the fingers during this operation. The excess of nonadherent powder is removed by inverting the specimen and allowing the container to drop 2.5 cm. (1inch) onto the table top. A second application of fine talc is then made by gently shaking or tapping a 300-mesh sieve held 7.5 cm. (3 inches) above the surface of the specimen, E O that a fine mist rather than agglomerated particles of the po\yder may accumulate on the specimen. This operation is continued with occasional weighings until a uniform film of talc weighing 0.025 gram per square inch (6.45 sq. em.) has been obtained. Uniformity in the thickness of the talc film is of great importance in obtaining reproducible results, for the thicker the layer of talc (up to a certain limit), the wider will be the ring formed. A drop of the saturant about 0.16 cm. (0.0625 inch) in diameter is placed upon the talc-dusted surface of the coating. This may be done most conveniently by plunging the end of a heated spatula or paring knife into the cold saturant and, after the excess has drained off, allowing a drop of suitable size t o fall on the dusted surface from a height of about 1.25cm. (0.5 inch). Several drops of the same or different saturants may be applied to a single specimen of dusted coating. The specimen is then placed in an oven maintained a t a temperature of 43.33" * 2.8" C., (110" * 5" F.) for a period of 72 hours. With some asphalts that are entirely free from strike-through tendencies towards each other, no reaction whatever will occur in this test, except for the very slow flattening of the spherical drop and the gradual yellowing of the dusting. With other asphalts that do have strikethrough tendencies, the drop will flatten more rapidly; and relatively early in the test a thin ring of a darker color than thesurrounding area will form on the dusted surface right around the periphery of the drop, and mill grow wider blacker, and glossier, till i t reaches a maximum width and gloss characteristic of that combination of asphalts, and of that type and quantity of dusting, after which i t spreads and darkens no further. The average width of the dark-brown or black ring of discolored talc that has formed a t the end of 72 hours around the periphery of the spot is determined to the closest 0.1 mm. by means of a scale of suitable dimensions and a good magnifying glass. This dark ring is usually sharply defined, and the vague penumbra that sometimes develops beyond the area of marked discoloration should be disregarded. A roughly quantitative estimate of the degree of bleeding to be anticipated in roofing in which any two asphalts are to be used, may be based on the width of ring of discolored talc that they develop in the exudation test. If no ring whatever is formed in that test not the least traces of bleeding will occur in the roofing made with the two asphalts. Although the technic described above has been found to be most reliable and convenient for routine work, many variations may be made in the method of test. For example, fine and coarse dustings of limestone, silica, mica, lampblack, slate, wood flour, asbestos, and other fibrous and nonfibrous products have been used with some degree of success, though some will form a wider and some a narrower ring than a n equally thick layer of talc. On the other hand, the total absence of dusting on the surface of the coating in the
test will prevent the formation of the characteristic ring, even when a film of the exudate is known to be present between the two asphalts involved. The effect of time and temperature in curing the specimen has also been investigated. The completion of the reaction will require weeks a t room temperature. At 43.33" C. (110" F.) the reaction will be substantially complete in about 3 days. Twenty-four hours at 60.0" C. (140" F.) and 5 hours a t 79.44" C. (1'75" F.) will give, very roughly, the bame results as 3 days a t 110" F.; but theinterfluxing of the coating, saturant, and exudate that occurs a t temperatures higher than 110" F. is objectionable and mars the distinctness of the reaction. Hence, 110" F. for 3 days was finally decided on
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b
Fresh
After 6 days
FIGURE 2 . PROGRESSIVE STAGES OF EXUDATION TEST
The progressive development of the exudation reaction a t 110" F. is demonstrated in Figure 2 by means of two square panels of coating shown in the successive stages of the test. The coating used on panel a differed as to source from that used on panel b, but both coatings \yere of approximately 20 penetration and 98.89" C. (210" F.) melting point (ring and ball). The two panels were coated and prepared in the standard manner described above. Three varieties of hard saturant ( H l , H2, and H3) were applied one below the other in that sequence on the left-hand side of each panel, and three soft saturants (SI, S2, and S3) were applied similarly on the right-hand side. The source and method of processing were different for each of the saturants, except that H3 and S2 were both produced by vacuum distillation from the same crude.
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ANALYTICAL EDITIOK
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The consistencies of the six saturants were as folloivs: TABLEI. WIDTHOF RING Saturant
Penetration
Saturant
Penetration
HI H2 H3
30
S1 82 d3
150-175 150-175 150-175
R .? 40
O n Coating -1 Saturant
After 1 day
Mm.
The picture- at the top of Figuie 2 shoa- the two panels before they were placed in the oven. The second set, immediately below. shows their condition after exposure for one day a t 110" F.; the third and fourth sets, after 3 and 6 days' exposure, respectively. It will be observed that no discolored ring was formed on either coating around saturant H1. However, saturants H3, P2, and S3 developed rings on both coatings, while saturants H2 and S1 developed rings on coating B but not on coating A . The rings widen with time to a definite maximum, and when the test is conducted at 110' F. they are of sub-tantially maximum width a t the end of 3 days. The average width of ring for each of the twelve combination. illu~tratedin Figure 2 is given in Table I.
Hard
H1
Soft
H3 dl 92 63
Hi
0 0 0 0 0 1: 0 0 0.25 0.9
.Liter After 3 days 6 days Mm. .Mm. 0 0 0 0 0 25 0.0 0 7 1 3
0 0 0 0 0 3 0.0 0.: 1
,
On After 1 day Mm 0 0 025 1 2
0.73 1.8 2.6
Coating E 4fter After 3 days 6 d a y s
Mm.
Mm.
0 0 035 2 0 1.0 2.9 2
0 0 065 2 2 1.0
,
3.4 5 0
Several years of practical experience with the exudation test have led to the conclusion that while it is safest practice to use only saturants and coatings t h a t show no ring whatever in that test, no visible bleeding n-ill occur in roofings made with a saturant and coating that in the standard exudation test a t 110" F. develop a ring not wider than 0.5 mm. I~ICEITED J a n u a r i 12 1038
Internal Electrolysis without Diaphragms Determination of Small Amounts of Nickel, Cobalt, and Copper in Ores Poor in These Metals J. J . LISRIE
AND
L. B. GINSBURG
Institute of Nonferrous ICletals, Moscow 17, c'. S. S . R.
T
HE authors ( 7 ) have slion-n the advantages of internal
electrolysis over external electrolysis in the determination of small amounts of metals, and have pointed out that a very simple apparatus without diaphragm may be substitut'ed for the complicated apparatus. proposed by a number of author; (1, 2, 4, 6, 11, 12), ~ i t h o u timpairing t'he accuracy of the analysis (6, 9, 10). I n addition (1) having selected a suitable anode, we obtaiii a definite potential difference not exceeded a t any moment during the course of the electrolysis but very slowly and gradually diminishing by 0.1 to 0.2 volt. Therefore by internal electrolysis it is possible to make separations which by external electrolysis require a constant' control of the cathode potential and a suitable apparatus. (2) The chief oxidizing process occurring a t the anode is the dissolution of the anode with the formation of the corresponding ions of this metal in the solution. This eliminates many difficulties of electrolysis due to the oxidation a t the anode of a number of ions to their higher valency states. We are therefore justified in hoping that small amounts of nickel and cobalt may be separated from large quantities of iron and from chromium by this method. This was the chief purpose of the present vork.
0.44 volt) would indicate that nickel and cobalt would be deposited on the platinum cathode, if the anode were an iroii plate. The potential difference. 0.19 x-olt. is sufficient for such a deposition. However, because of the very small overvoltage of hydrogen on nickel and cobalt. these nietals cannot be deposited by electrolgsib in an acid medium, TI-liilein ammoniacal solutions they form complex ions, as a result of which their potentials are shifted and hecome more negative than in an acid medium.
-4pparatus The apparatus for internal hydrolysis used by the authors is shown in Figure 1 (and in Figure 1 of an earlier article, 7 ) . The cathode is a Fischer's platinum gauze; the anode is a metallic plate of iron, zinc, or aluminum, depending on the metal to be yecipitated and on the conditions of precipitation. To secure a ull contact, the electrodes are firmly held together by a copper or aluminum clamp, which replaces the copper wire formerly used ( 7 ) and somewhat simplifies manipulations. The places of contact must a1way.c he well cleaned n-ith emery paper before proceeding to work. Determination of Nickel and Cobalt The normal potentials (E,) of nickel, cobalt, and iron (Em, s,+-, 0.25 volt; Eco;co --, 0.255 \rolt: E p e , pB- + ,
FIGURE1
