Jan., 1913
T H E J O U R l V i l L OF I N D C S T R I A L A!\:D E A - G I N E E R I S G C H E A 4 I S T R Y THERMOCOUPLES
We are investigating the thermoelectric properties of the couple, tungsten-molybdenum. The electromotive force increases with the temperature up t o about 540' then decreases and passes through zero millivolt a t about 1 3 0 0 ~ . We have found this couple very convenient for high temperature measurements in the tungsten-hydrogen furnace. STANDARD WEIGHTS
A material suitable for standard weights must preferably be hard yet plastic, i t must not be easily scratched nor marred, but still not be so hard that i t will chip or break; furthermore, i t must withstand the action of the atmosphere and finally i t must be small in bulk. Now wrought tungsten can be made so hard that i t will readily scratch glass and still be ductile; furthermore, the density is high (19.3t o 21.4) and i t is unaffected by the atmosphere. Tungsten weights remain wonderfully constant. T U N G S T E N CELLS
9
+
The heat of formation of HCN is: C,H, N, = 2HCN - 9400 cal.1 We are making acid-proof dishes and tubes out of tungsten. Furthermore, tungsten wire recommends itself as a unit resistance since it can be made absolutely pure, can be easily duplicated and is not corroded. Since tungsten is non-magnetic and elastic i t is being tried out in electrical meters, replacing the phosphor-bronze springs. Similarly watch springs could be made which would never become magnetized. Finally we might mention: tungsten pen points, tungsten drawing dies, tungsten knife blades, tungsten reinforced asbestos curtains and fire-proof coverings, etc. TABLEO F PHYSICAL AND CHEMICAL PROPERTIES OF DUCTILET ~ N G S T E N Density, 19.3 to 21.4 Tensile strength, 322 t o 427 kg. per sq. mm. Young's modulus of elasticity, 42,200 kilograms per square mm. (steel 20,000): i. e . , twice as elastic as steel. Melting point, 3177 (Langmuir) 3 1 0 0 h . 60 (v. Pirani & 3teye.r). Boiling point. 3700' (?). Thermal conductivity, 0.35 gram cal. per cm. per sec. per 1' ( P t , 0.166) (calculated, see foot-note 1, column 2, p. 8). Expansion coefficient, 4.3 X ( P t , 8.8 X Specific heat, 0.0358 (Weiss). Resistivity (25') hard: 6.2 microhms per cu. cm. ; annealed: 5.0 microhm per cu. cm. Temperature coefficient of resistance, 0.0051 (Oo-17O0). Hardness, 4.5 to 8.0 (Mohs scale). Insoluble in HC1, H2S04, " 0 8 , HF. NaOH, KOH, (aq.) KZCr20: H2SO4 (see foot-note 2 , column 1, p. 8). Soluble in mixtures of €IF and "03, and in fused nitrates, nitrites and peroxides. The boiling point of the metal has not yet been determined. The Young's Modulus of Elasticity we determined with a wire 0.00648 cm. in diameter 2nd 784.86 cm. long. The smallest weight (P)was 250 and the largest 1125 grams. The elastic elongation was 0.35 cm. .for the smallest weight and 1.65 cm. for the largest. The average for five different weights was 42,200. The hardness values were determined with the scleroscope and the values translated into the Mohs scale. GESERALELECTRICCO. SEWARK, S . J.
We have taken up the study of the electrochemical behavior of tungsten and have made up a series of cells and combinations. All measurements were made a t 2 5 ' and compared with the calomel electrode as + standard. Our readings for the cell tungsten, aqueous sodium hydrate, potassium chloride, calomel, mercury are : 5 i V NaOH, 0.68; 2 iY, 0 . 6 2 ; A', o 5 7 ; S, 0.525; I/,,, iV,0 . 5 0 ; A',0.48; S , 0 455; '/,,, -I-, 0.445; I / N ~ , 0.380; ~ ~ and 0.0 iV, 0.06 volt. I n the last cell the tungsten rod was immersed in distilled water. The addition of small amounts of impurities to the tungsten metal causes the tungsten-sodium hydrate electrode t o assume E. M. F. values that approach t h a t of zinc in zinc sulfate. BLUE GELATINE COPPERZ The values for potassium hydrate are similar t o B y ~ V I L D E RD. BANCROFT A N D T. R. BRIGGS those for sodium hydrate. The E. M. F. of the cell Copper and the copper alloys such as brass and the Hg-Hg,~',O,, Na,WO, solid-Na,WO, sat. so1n.bronzes lend themselves very readily to artistic decorasolid Na,WO,--W was found to be 0,505 volt and tion by means of colored superficial films or "patinas." promises to be a good standard cell. Great as is the variety of colors which may thus be imparted to copper, nevertheless a rich and true MISCELLAKEOUS APPLICATIONS Besides the applications of tungsten cited above, blue patina for this metal is practically unknown. I t was while seeking such a blue surface film that the many others have been but partly worked o u t and electrolysis of copper acetate solutions containing others merely suggested. Owing t o its chemical stability the . finest sizes gelatine was first performed. One gram of gelatine was dissolved in 325 cc. of a I per cent. solution of wire down to 0 . 0 0 0 2 " or 0.005 mm. in diameter are well adapted for galvanometer suspensions and of cupric acetate and this mixture electrolyzed between carefully cleaned and burnished electrodes of sheetfor cross hairs in telescopes. I t has also been suggested to use these fine wires in surgical operations copper. The electrolysis was continued for five in place of the ,coarser gold and silver wires. A minutes a t 'a cathode (and anode) current density further suggestion is the use of the wire in musical which varied between 0.15 and 0.45 amp/dma. The instruments. The tensile strength and elasticity process was carried out a t room temperature. The electrolysis performed, the cathode was found of tungsten wire are exceptionally high (see table beto be covered on its inner surface with a thin, pale low). brown deposit, which, when rubbed with the fingers, I t could be used to advantage in climates where was seen t o possess a peculiar, slippery surface caused steel is readily corroded. We are investigating the formation of hydrocyanic by a very appreciable amount of gelatine deposited acid gas by passing over heated tungsten wire mixtures simultaneously with the metallic copper. No gas
+
of nitrogen and acetylene or methane.1 1
Compare Berthelot and Lipinski, 2.Elekirochemie, 17, 287.
Wartenburg, Z . j . anorg. Chem., 62, 299. presented a t the Eighth International Congress of Applied Chemistry, New York, September, 1912.
* Paper
IO
T H E JOURNAL OF I N D U S T R I A L A N D EIVGINEERING C H E M I S T R Y
Jan., 1913
became visible a t either pole during the passage of plete success and are interesting in their application the current. t o metallochromy. I n itself, this pale brown cathode deposit gave no 4 . Other Factors.-The best results were obtained indication of its peculiar properties and it was by with copper acetate or propionate solutions made chance only t h a t these were discovered. An electrode, up in the proportion of I or 2 parts b y weight of the freshly coated with a layer of the gelatine-copper, crystallized salt t o I O O parts of water. The electrolyte was by a n oversight allowed t o remain in the solution should be neutral or a t most but very slightly acid. of copper acetate from which the film of metal had The current density must be low-between 0.15 and just been deposited a n d the current was turned off. 0.45 amp./dma-and the process need not exceed On removing the electrode from the solution, it was 5 minutes in duration. The nature of the metal used noticed t h a t the brown color originally possessed b y as cathode is of little importance as long as the copper the cathode film had given place t o a purplish blue solution is not decomposed. Thus with nickel, brass, of extraordinary brilliance and beauty. This led t o and platinum, good deposits were obtained a s adherent further experiments. cathode films which developed a good blue color. 5 . The Development of the Blue Color.-A 5 per cent. A second electrode was then coated with a film of gelatine-copper and, after careful rinsing with copper acetate solution containing no gelatine was cold t a p water, immersed in a 5 per cent. solution used as the developing bath throughout this work, of copper acetate containing no gelatine. Straightway although a copper propionate solution may also be there ensued a remarkable series of color changes employed. Copper formate developer gave less satisupon the surface of the copper deposit ; hues of startling factory results. A large number of other salt soluevenness and intensity followed each other in regular tions were then tried as developers with practically succession until the electrodes had acquired a magnifi- no success, Thus in normal copper sulfate solution cent deep-blue coloration. This process we shall a film of gelatine-copper was colored a dull. dark speak of as a “development,” since it bears a certain indigo. I n N / 5 0 copper sulfate a fairly good blue resemblance t o the development of the silver image color was developed although the colors obtained with sulfate solutions are distinctly inferior t o those in the process of photography. prepared with acetate developer. Very dilute copper EXPERIMENTAL nitrate oxidized the film t o dark brown copper oxide I. Efject of Gelatine.-After the process of developwhile a chloride solution spoiled the deposit entirely. ment had been discovered, a more systematic study Several oxidizing solutions were next used with of the formation and nature of gelatine-copper was negative results. Potassium chromate, bichromate, undertaken. I t then became evident t h a t gelatine permanganate, perchlorate, chlorate, and persulfate must be present in the electrolyte and t h a t this colloid failed t o give even a trace of blue coloration. The exerted a tremendous influence upon the nature of films were usually oxidized slowly t o brown cupric the cathode deposit. The term “gelatine-copper” oxide. Reducing solutions gave no development. was thus justified, The optimum gelatine concentraThe film of gelatine-copper was unaffected b y dilute, tion was found t o lie between 0.25 and 0.66 per cent. warm, hydrazine hydrate and underwent accelerated The electrolysis of copper acetate solutions containing blue development in copper acetate after such treatno gelatine failed t o give the developable films nor was ment. it possible t o substitute other hydrophile colloids A solution of sodium acetate gave no blue coloration such a s starch or gum-arabic for gelatine or glue. of the copper film nor was i t otherwise with the acetate 2. Nature of Electrolyte.-Electrolysis of copper solutions of other metals. Hence this phenomenon formate, acetate, and propionate solutions containing must be a function of the copper contained in the gelatine resulted in cathode films which developed developing :elutions. blue in copper acetate although this development was 6. Reverse Development.-An electrode, covered with imperfect in the case of the deposits from the formate a deep blue film, was immersed in a very dilute aqueous solution. Copper sulfate solutions of different strengths solution of hydrazine hydrate and, in a short time, and varying gelatine content failed absolutely t o give bubbles of nitrogen began t o form on the blue surface. developable deposits. Similar results were obtained The blue color then slowly faded away. until. passing with solutions of copper nitrate and chloride. in the reverse direction through the series of colors 3. Effect of Temperature.-Variation of the tempera- previously described, the film of gelatine-copper ture a t which the electrolysis was perfoimed led t o again took on its original brown color. This process interesting results. Between 20’ and 40° C., the was called a “reverse development.” cathode deposit was of the usual pale brown color The reverse development completed, the electrode and gave a more or less satisfactory color-develop- was rinsed in distilled water and once more immersed ment t o blue in copper acetate. At 50’ C. or a t higher in the usual copper acetate developer. The blue temperatures, the cathode deposit was colored a bright color formed again quickly, but was a bit thin and ked or a brick-red and was unaffected by the developing uneven. solution. Between 55’ and 60’ a short electrolysis I f a film of gelatine-copper is allowed t o stand with a low current density gave a gold-colored but undeveloped for several hours, it completely loses its very thin film which had a rather iridescent appearance. power of developing in copper acetate. This is probThese gold and red films can be lacquered with com- ably due t o its oxidation b y the air because i t was
Jan., 1913
T H E JOURA’AL OF I N D C S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
found t h a t treatment of such a “dead” film with hydrazine hydrate was sufficient t o regenerate its powers of development. The same result was obtained with a film after immersion in warm, dilute hydrogen peroxide-no development occurred until the layer of oxide so produced had been reduced with hydrazine. THEORY AND CONCLUSIONS
Schiitzenberger, b y the electrolysis of copper acetate solutions, obtained a t the cathode a peculiar form of copper; and, being unable t o explain its unusual behavior, he announced it a s a n allotropic modification. Wiedemann incorrectly contended t h a t the new form of copper was really the oxide of t h a t metal, while recently Benedicks has advanced the idea t h a t we have t o deal with a solid solution of acetic acid in copper. It can be shown, however, b y a careful study of their results by, and consideration of, the facts of colloid chemistry, t h a t the allotropic copper of Schutzenberger is merely the normal metal in the form of a n irreversible colloid gel. The same conclusion is applicable to the deposits of gelatine-copper described in this paper. The gelatine acts here a s the “protecting colloid,” migrates b y cataphoresis t o the cathode, and there inhibits the growth or crystallization of the copper nuclei. Gelatine-copper is a n irreversible gel of colloidal copper. The whole phenomenon is b u t another example of the marked influence of organic and other colloidal substances upon metals prepared b y electrolysis, accounts of which have appeared in the recent papers of Muller and Bahntje, Snowdon and others. What is the nature and mechanism of the process of the color development? This is indeed a difficult problem, chiefly because of the exceeding small quantities of reacting material of necessity dealt with. The blue, although a superficial color, is nevertheless not the color of a thin film of gelatine or oxide bringing about interference disturbances in the reflected rays of light. Nor does i t seem t o be the color of a definite chemical compound. The blue layer does contain oxide as is shown b y its action with hydrazine and yet i t cannot be prepared b y any process of simple oxidation. It cannot be produced by the partial coagulation of the copper gel. It was shown b y Wiedemann t h a t Schutzenberger’s copper possesses the power of adsorbing very considerable quantities of copper oxide from copper acetate solutions. This observation furnished the clue t o the process of development. The color changes t h a t appear upon the film are the result of a surface adsorption of h y d r o u s copper oxide from the copper solzttion. The hydrous copper oxide is present as a suspension in very appreciable quantities in the acetate or propionate solutions, being the product of hydrolytic dissociation. This being the case, we should expect the best development with the acetate solutions and but little color effect with the sulfate and chloride developers. The reversal of development caused by hydrazine is due to the reduction of the adsorbed oxide. There seems to be a certain definite concentration of oxide
I1
in the copper film necessary for the production of a blue color. As the concentration of the oxide increases by continued adsorption, the film passes through the series of colors so distinctive of the development. I n conclusion it can be said in support of this hypothesis t h a t it is in accord with many of the established facts in colloid chemistry and explains in the best possible manner this decidedly obscure phenomenon. Stannic oxide adsorbs gold from suspension and forms the “Purple of Cassius;” under very special conditions colloidal copper adsorbs hydrous copper oxide and similarly gives a n intensely colored adsorption compound. SUM M . 4R Y
The electrolytic production of a form of colloidal copper was performed with certain copper solutions containing gelatine. This new form of copper develops a remarkable series of colors when immersed in certain copper solutions, a peacock-blue being the finest color obtained. The process of development is a n adsorption of hydrous copper oxide by the surface of the colloid film. There have been described methods of coloring metal objects gold, golden brown or red. CORNELL UNIVERSITY ITHACA.NEW YORK
THE CLASSIFICATION OF BITUMINOUS AND RESINOUS SUBSTANCES’ By HERBERTABRAHAM
The terms bitumen, asphalt, resin, tar, pitch, etc., are in common use, yet i t is surprising to note how inadequately they are defined in most of the standard works and text-books. This may be explained b y the fact t h a t these words originally had limited meanings, but in keeping pace with the progress of science they were extended in scope until they completely outgrew their original bounds. I t is probable t h a t each of the expressions a t first pertained t o the aggregate properties characteristic of some typical substance closely associated with the processes of daily life. Thus, the generic term “resin” originated in the word “rosin,” and it even now alludes t o substances resembling ordinary rosin in appearance and physical properties. Similarly our comprehension of the generic term “wax” is based largely on the physical characteristics of the oldest known wax; namely, common beeswax. From time to time, as new substances were discovered in nature, or produced in the arts, the meanings of these words were arbitrarily extended t o include them. This resulted in a certain amount of overlapping and consequent confusion. AS the chemistry of these substances was investigated, this was in certain cases adopted as a n additional means of differentiation. But we are still forced t o rely principally upon the physical characteristics of these groups of materials, for even to-day comparatively little accurate information is available with respect t o their chemical composition. I t is probable, however, 1 Paper presented a t the Eighth International Congress of Applied Chemistry, New York, September, 1912.
