Acheson Graphite Research Articles

A Search for Preferentially Directed Electron Velocities in Crystalline Graphite with the Multicrystal Spectrograph

The author's theory of the broadening of the Compton line as a Doppler effect of electron velocities is briefly reviewed and it is pointed out that only the component velocity along a direction which nearly bisects the angle between primary and scattered x-ray beams should be effective in broadening the line. Crystalline Ceylon graphite possesses properties which lend hope to the belief that a class of weakly bound or structure electrons in this crystal might have momenta restricted uniquely to parallelism with one plane in the crystal: the (0001) plane. A composite scatterer was built up out of blocks consisting of the crystal flakes all orientated with their (0001) planes in mutual parallelism and the blocks in turn were so orientated that the normals to these planes bisected the angle formed by the primary and scattered x-ray beams. If the electron momenta are orientated parallel to the plane of the graphite flakes one should expect the contribution of such electrons to the shifted scattering to give a sharp line or peak superposed on the broader structure caused by the remaining isotropically distributed momenta. Details of the experimental set-up are described and the spectrum obtained from scattering by the Ceylon graphite scatterer is compared with the spectrum from an isotropic Acheson graphite scatterer. The breadth and structure of the shifted line proves to be quite identical in the two cases and the conclusion is drawn that if a class of electrons having selectively orientated momenta exists in the crystal-line graphite it constitutes less than 5 percent of the total number. The bearing of this result on related questions is discussed.

Carbon Contacts

THE contact difficulties to which I referred were those of fifty years ago with light or hesitating contacts backed by insufficient volts. I did not intend to imply that at the present time with new materials and abundant volts contacts need give any trouble. I have for a long time recommended Acheson graphite made at Niagara, from which all other matter has been volatilised, and this, I expect, is what Mr. Turnbull has used. There are also the more modern mercury in nitrogen contacts which are admirable where the larger movement necessary to operate them and the slight time delay do not matter.

The Band Spectrum of AsH

THESE bands were obtained by photographing a carbon are, the negative electrode of which had been drilled and filled with arsenic, run in an atmosphere of hydrogen at a potential of 110 volts. No bands were obtained with the arsenic in the positive electrode. The electrodes were composed of Acheson graphite. The spectrograph used was a Hilger three-metre quartz prism instrument.

Intercombinations in the Arc Spectrum of Carbon

PROF. A. FOWLER and E. W. H. Selwyn have recently classified the lines of the arc spectrum of carbon, and identified triplet as well as singlet terms, but no intercombinations have apparently been obtained. Recently I took a heavy arc spectrum of Acheson graphite in the region λ2000, and obtained a number of lines, some new, and others recorded by previous observers like McLennan, Hutchinson, and others. I was able to identify the following intercombination lines:

The True Temperature Scale of Carbon

Spectral emissive power of Acheson graphite at 0.660μ. — The spectral emissive power of Acheson graphite for the wave-length 0.660μ has been determined for the temperature range from 1250°K to 2700°K. The observations were made on a small tubular graphite resistance furnace with a hole in the wall and are best summarized by the relation: e=0.984-5.8×10^-5T. Measurements of the temperature distribution along the furnace afford determinations of the ratio of resistivity to thermal conductivity at three temperatures.

The Variation in the Resistance of Carbon and Graphite with Temperature

Change of resistance of carbon and graphite with temperature, ---190\ifmmode^\circ\else\textdegree\fi{} to 2000\ifmmode^\circ\else\textdegree\fi{}C.---For the higher temperatures the specimens were kept in vacuum and heated by a current passed through them, temperatures being measured optically. Several specimens of untreated carbon filament made from braided silk, showed a resistance decreasing linearly with temperature, the ratio to the resistance at room temperature being equal to $1.07\ensuremath{-}.000225T$, where $T$ is temperature absolute. In the case of a metallized filament (Gem), the resistance decreased to a minimum for 400\ifmmode^\circ\else\textdegree\fi{}C and then increased steadily. Acheson graphite, purified somewhat by heating, showed minimum resistance at about 600\ifmmode^\circ\else\textdegree\fi{} and then increased linearly. These results do not fit any law which has yet been proposed. Effect of air. Graphite in the presence of air at about 1/4 atm. pressure had a resistance at 500\ifmmode^\circ\else\textdegree\fi{}C about 4 per cent lower than in a vacuum. This effect decreased with temperature, being absent at room temperature.Change of length of carbon rod at about 2200\ifmmode^\circ\else\textdegree\fi{}C.---An increase in length was observed, which resulted in permanently bending the specimen.

HYDROPHILIC AND HYDROPHOBIC COLLOIDS AND THE INFLUENCE OF ELECTROLYTES ON MEMBRANE POTENTIALS AND CATAPHORETIC POTENTIALS

1. In order to be able to compare the effects of electrolytes on membrane potentials and cataphoretic potentials it seems necessary to distinguish between the charging and depressing effect of electrolytes on these potentials. Only low concentrations of acids and alkalies have a charging effect on the membrane potentials of proteins, while low concentrations of neutral salts have only a depressing effect; in the case of the cataphoretic potentials, low concentrations of salts have a charging effect as have also low concentrations of alkalies and in some cases low concentrations of acids. This difference finds its explanation in the difference of the origin of the two potentials and there can therefore be no common theory for the charging effect of electrolytes in the two cases. 2. There exists, however, an analogy in the depressing action of electrolytes on the two types of potentials inasmuch when the maximal P.D. is reached, all three kinds of electrolytes, acids, alkalies, and neutral salts, have a depressing effect on both types of potentials (taking into due consideration the effect of changes in the hydrogen ion concentration). 3. This depressing effect is adequately explained for the membrane potentials of protein solutions and protein gels on the basis of the Donnan equilibrium, and the question arises whether the same explanation may also hold for the cataphoretic potentials. 4. The active ion in the depressing action of electrolytes on membrane potentials as well as on cataphoretic potentials has the opposite sign of charge from that of the colloidal particle. It had been shown before that only the valency but not the chemical nature of the active ion determines the depressing effect in the case of membrane potentials and it is shown in this paper that the same is true for the cataphoretic potentials of particles of collodion, mastic, Acheson's graphite, and denatured egg albumin. 5. It is shown that the same valency rule holds also for the effect of acids on the cataphoretic potentials of collodion particles coated with gelatin, and that the ratio of the effect of dibasic to that of mono-basic acids is approximately 0.66, as Donnan's theory of membrane potentials would demand. 6. If we have a right to conclude from the validity of the valency rule for cataphoretic potentials that the depressing effect of electrolytes on the cataphoretic P.D. is determined by the Donnan equilibrium, we can understand the analogy between the depressing action of electrolytes on membrane potentials of hydrophilic colloids and on the cataphoretic potentials of hydrophobic colloids. We can also understand the analogy between the influence of electrolytes on the precipitation of hydrophobic colloids and on the depression of the values of all those properties of hydrophilic colloids which depend on the Donnan equilibrium, since the precipitation of hydrophobic colloids occurs when the cataphoretic P.D. is depressed below a critical value.

THE INFLUENCE OF THE CHEMICAL NATURE OF SOLID PARTICLES ON THEIR CATAPHORETIC P.D. IN AQUEOUS SOLUTIONS

1. The effect of eight salts, NaCl, Na(2)SO(4), Na(4)Fe(CN)(6), CaCl(2), LaCl(3), ThCl(4), and basic and acid fuchsin on the cataphoretic P.D. between solid particles and aqueous solutions was measured near the point of neutrality of water (pH 5.8). It was found that without the addition of electrolyte the cataphoretic P.D. between particles and water is very minute near the point of neutrality (pH 5.8), often less than 10 millivolts, if care is taken that the solutions are free from impurities. Particles which in the absence of salts have a positive charge in water near the point of neutrality (pH 5.8) are termed positive colloids and particles which have a negative charge under these conditions are termed negative colloids. 2. If care is taken that the addition of the salt does not change the hydrogen ion concentration of the solution (which in these experiments was generally pH 5.8) it can be said in general, that as long as the concentration of salts is not too high, the anions of the salt have the tendency to make the particles more negative (or less positive) and that cations have the opposite effect; and that both effects increase with the increasing valency of the ions. As soon as a maximal P.D. is reached, which varies for each salt and for each type of particles, a further addition of salt depresses the P.D. again. Aside from this general tendency the effects of salts on the P.D. are typically different for positive and negative colloids. 3. Negative colloids (collodion, mastic, Acheson's graphite, gold, and metal proteinates) are rendered more negative by low concentrations of salts with monovalent cation (e.g. Na) the higher the valency of the anion, though the difference in the maximal P.D. is slight for the monovalent Cl and the tetravalent Fe(CN)(6) ions. Low concentrations of CaCl(2) also make negative colloids more negative but the maximal P.D. is less than for NaCl; even LaCl(3) increases the P.D. of negative particles slightly in low concentrations. ThCl(4) and basic fuchsin, however, seem to make the negative particles positive even in very low concentrations. 4. Positive colloids (ferric hydroxide, calcium oxalate, casein chloride-the latter at pH 4.0) are practically not affected by NaCl, are rendered slightly negative by high concentrations of Na(2)SO(4), and are rendered more negative by Na(4)Fe(CN)(6) and acid dyes. Low concentrations of CaCl(2) and LaCl(3) increase the positive charge of the particles until a maximum is reached after which the addition of more salt depresses the P.D. again. 5. It is shown that alkalies (NaOH) act on the cataphoretic P.D. of both negative and positive particles as Na(4)Fe(CN)(6) does at the point of neutrality. 6. Low concentrations of HCl raise the cataphoretic P.D. of particles of collodion, mastic, graphite, and gold until a maximum is reached, after which the P.D. is depressed by a further increase in the concentration of the acid. No reversal in the sign of charge of the particle occurs in the case of collodion, while if a reversal occurs in the case of mastic, gold, and graphite, the P.D. is never more than a few millivolts. When HCl changes the chemical nature of the colloid, e.g. when HCl is added to particles of amphoteric electrolytes like sodium gelatinate, a marked reversal will occur, on account of the transformation of the metal proteinate into a protein-acid salt. 7. A real reversal in the sign of charge of positive particles occurs, however, at neutrality if Na(4)Fe(CN)(6) or an acid dye is added; and in the case of negative colloids when low concentrations of basic dyes or minute traces of ThCl(4) are added. 8. Flocculation of the suspensions by salts occurs when the cataphoretic P.D. reaches a critical value which is about 14 millivolts for particles of graphite, gold, or mastic or denatured egg albumin; while for collodion particles it was about 16 millivolts. A critical P.D. of about 15 millivolts was also observed by Northrop and De Kruif for the flocculation of certain bacteria.