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By Z. Z. Öztürk, N. Sarica, A. H. Üçisik, C. Bindal

"Titanium oxide films were fabricated on commercially pure titanium surfaces via anodization procedure. Anodization parameters, anodization time and voltage were altered, whereas temperature and chemical composition of anodization bath were kept constant. The main idea in this study is to obtain rough titanium-oxide surfaces. The type and feature of titanium oxide formed were observed via SEM and EDX analyses. What was revealed from SEM and EDX analyses were combined with Ti-O phase diagram in order to make judgment on the type of phases obtained, e.g. solid solution and/or compounds. Studies on the different regions of each sample showed that surfaces consist of different titanium oxide compounds with various O/Ti ratios in nano level and solid solutions varying in terms of chemistry on the same sample. Thus together rough surfaces and inhomogeneous distribution of "titanium oxides" were obtained. It was also found that when anodization time and voltage were increased, more granular surface with higher O/Ti atomic ratio was obtained."

Jan 1, 2015

By J. E. Gosline

IN any theory of a hydrodynamic nature dealing with the vertical flow of gas-liquid mixtures in pipes, the two factors that present the greatest difficulty are the relative motion between the phases and the energy loss resulting from turbulence work. The former has generally been referred to in the literature as "slippage" and the latter as "fric-tion." A third factor of importance is the nature of admixture between liquid and gas for both the relative motion between the phases as well as the turbulence work are functions of the type of mixture. Although much work of a general nature has been performed on the vertical flow problem, there have been very few attempts made to study experimentally the factors involved in the phenomenon individually. Of these, perhaps the most notable is the work of Moore and Wilde1 on slippage. Some writers on the subject have assumed that over a wide range of operating conditions the controlling type of mixture, is one in which gas bubbles of uniform size are distributed throughout the liquid, and that the data obtained from experiments on the motion of single bubbles through various liquids may be used in evaluating the slippage. Ver-sluys2 has further assumed another controlling type of mixture in which the liquid occurs as a dispersed phase within the gas and applies data on the fall of drops of water in air to calculating the relative velocity. It was for the purpose of studying the applicability of data on single bubble motion to the slippage factor and to further observe the nature of mixtures that a research program was conducted at the University of California during 1932 and 1933. These experiments formed a basis for

Jan 1, 1935

"8.1. IntroductionThe stoichiometry of most named platinum-group minerals (POM) is known (cf. Cabri, 1981b, in Chapter 7), but, because these minerals are subject to a wide range of element substitutions, representative analyses require treatment in a separate chapter (section 8.2). The analyses, in all cases done by electron microprobe, are grouped in sections according to the principal platinum-group element (POE) for each POM, and then follow sequentially with increasing amounts of the principal POE starting with the ideal composition, when known. In order to facilitate reference to specific POM by name, an alphabetical listing is also given (Table 8.1). A range of compositions, in addition to one or several ""representative"" analyses, is given for some POM when more than one analysis has been reported for a particular locality. The tables of POM analyses (Tables 8.2 to 8. 76) include at least one analysis for every locality for which data have been published, to the best of the authors' knowledge. All analyses are referenced for locality and publication source, and include several unpublished analyses (all but one done at CANMET). Most analyses have been rounded off to one decimal place for amounts more than one per cent and their formulae calculated on the basis of an even number of total atoms. In all tables, ''n.d.'' stands for elements sought for but not detected and a dash signifies elements not sought, or when these haven't been specificed in the publication source.Section 8.3 contains tabulated analyses and, in some cases, also includes a critical assessment of POE-bearing minerals in which the POE occur in trace or minor quantities. The organization of the data in this section is by mineral groups; e.g., sulphides, sulpharsenides, silicates, etc. Some of these data are also discussed in Chapter 4 by Crocket (1981) and are discussed briefly in Chapter 6 by Crocket and Cabri (1981)."

Jan 1, 1979

By Juarez Linhares

A mini sinterização processo JL patenteada sob o número PI-9202973-6, é caracterizada por soprar o ar pelo fundo da panela, dispensando o uso de grelhas, caixa de ignição além de proporcionar um baixo consumo de energia elétrica, o que se traduz em vantagens técnicas e econômicas ao processo de sinterização.

Aug 16, 2017

By W. A. Roliff

The renewed interest of the past few years in the Appalachian and Michigan oil provinces has not, as yet, created any marked increase in activity in Southwestern Ontario. During 1960 development drilling in-creased somewhat over 1959, but exploratory drilling decreased slightly. More attention was devoted to the deeper horizons, but lake drilling de-creased considerably. Oil production reached a new peak and gas production increased slightly. During 1960 an interesting oil and gas discovery was made in the Cambrian and gas discoveries six miles off-shore in the eastern part of Lake Erie were made in the Clinton-Cataract zone of the Silurian. This paper reviews activities during 1960, summarizes the discoveries made to-date and the pertinent exploration data relating to the prospects of the region and discusses some of the economic aspects of exploration and development. D URING the last few years there has •been a marked renewal of interest in the old petroleum

Jan 1, 1961

By William M. Thornton

[Owing to the comparatively high freezing point of nitroglycerin (14, 15, 16, 17, 18, 23, 37, 38)3/ - 1.9° C. and 13.0° C. for the labile and stabile modifications, respectively, as determined by Hibbert (16) - manufacturers of dynamites have incorporated into the liquid portion of these composite explosives various substances capable of participating in an explosion, to depress the above-mentioned freezing point. Aromatic nitro-compounds, chiefly nitrobenzenes, nitrotoluenes, and nitronaphthalenes, have been used to a considerable extent (11), but such nitrosubstitution products have not proved altogether satisfactory, as has been shown clearly by Naoúm. (14). Consequently there has been a strong tendency in recent years to replace them with one or more of several nitric esters, among which the following (29, 35) have been prominent: Dinitrochlorhydrin (monochlorhydrin dinitrate); nitrosugars, for example, sucrose octanitrate (19); tetranitrodiglycerin (diglycerin tetranitrate); nitroglycol (ethyleneglycol dinitrate); and diethyleneglycol dinitrate (13, 46, 47). Of these, nitroglycol (33, 4l, 45, 48, 49, 65) is outstanding in importance. As the Bureau of fines is naturally interested in the analytical chemistry of the "explosive oils," it seemed desirable to bring together in this report the widely scattered experimental work covering the problem of differentiation that has appeared in various chemical and physicochemical publications.]

Jan 1, 1941

By W. T. Abel

Laboratory tests were conducted with a closed, recycling system to evaluate the effectiveness of solid-in-gas suspensions as heat transport mediums. Micronized graphite in helium or nitrogen was circulated by a centrifugal compressor to determine the feasibility of the method and heat transfer capabilities of the mediums. Suspensions were circulated without plugging or eroding the compressor or piping. At low flowrates and light (0.1 to 0.2 volume-percent) graphite loadings, slightly less power was required to transport a given amount of heat with suspensions than with helium alone. Graphite deposition on the heat exchange surfaces of the cooler decreased the heat transfer effectiveness at higher solids concentration. Efforts to eliminate deposition are described.

Jan 1, 1963

By F. Guo

"The leaching kinetics of zinc sulphide concentrate was studied under total pressures ranging from 0.3 MPa to 0.5 MPa and leaching temperatures ranging from 358 K to 378 K. The apparent activation energy of leaching reaction under different total pressures was calculated. The results show that for the extraction of zinc at low-temperature pressure leaching is controlled by an interfacial chemical reaction. This was supported mineralogical analysis of the leaching residue. The kinetic equation for low-temperature pressure leaching of zinc sulphide concentrate was further established by quadratic regression on the basis of shrinking core model.INTRODUCTIONThe Roast-Leach-Electrowinning Process (RLE) is the primary route for zinc production and responsible for more than 85% of the total zinc production (Souza et al., 2007). During the roasting of zinc concentrates, fugitive SO2 causes pollution. The prevention of SO2 emissions from the RLE process can be one of the challenges to this technology (Deller, 2005). In the 1980s, the Zinc Pressure Leach (ZPL) process changed the concept of zinc hydrometallurgy, in which zinc sulphide concentrate is directly leached at approximately 423 K and approximately 0.7 MPa oxygen overpressure and the sulphidic sulphur is oxidized into elemental sulphur so that the pollution by SO2 is completely avoided. Since 1981, five zinc plants have adopted the ZPL process either for expansion by integration with existing roasting facilities, or for the production of zinc without any roasting at all (Collins et al. 1994; Barth et al. 1998). The innovation of the ZPL process has made the zinc industries more competitive although it needs an autoclave. The direct leaching technology of zinc is still in development."

Jan 1, 2012

By D. Nilsson, B. Aaro

To find out if there are any potential savings in "in-the-wall haulage for open pits," the Swedish companies ASEA and Kiruna-Truck in 1984 gave us financial support to study this solution in more detail. In the study, the use of in-the-wall haulage was studied for three hypothetical open pits with different sizes and shapes. Annual ore production rates also varied. A part of this thor¬ough study was published by the Swedish Mining Research Foundation (see Report F 8444, "The Use of Electric Trucks and In-the-Wall Haulage in Open-Pit Mining," in Swedish with an English Summary). Although in-the-wall haulage is of interest in some open pits, the local terrain is important for profitability. The authors do not think in-the-wall haulage is of any major interest for the mining industry. The following is a summary of some of the author's findings. To place the haul road in the wall is not of interest in open pits with declining metal contents in the bedrock. In such mines, the volumes from the haul roads will not yield reve¬nues. The cost per m3 for an underground haul road is much higher than for a haul road in the pit. This means that it is only of interest to place the haul road in the wall when mining gets deeper than about 50 m (165 ft). In-the-wall haul roads will reduce flexibility in the pit, and it will make necessary the use of smaller equipment with lower productivity and higher costs per ton. As Hustrulid, et al. show (Table 4), excavation savings of material hauled are very low, $0.10 to $0.25/t (0.09 to 0.27 per st). The extra operating cost, due to lower productive equip¬ment, will normally be much higher and thus destroy the whole idea with in-the-wall haulage. If electric trucks are profitable for in-the-wall haulage, it is normally also profitable to use electric trolley assist for trucks on the haul road in the pit. But the profitability of using electric power is different in different countries, and depends on the relation between the cost for electric power and diesel fuel. In the US, diesel fuel is inexpensive compared with electricity, but in a country like Sweden, diesel fuel is much more expensive. In most open pits, the trucks have to move a considerable distange from the loader until they reach a final haul road in the wall. A trolley line along such temporary haul roads will be exposed to flyrock. It is normally less expensive to perform rock support from the open pit than from underground ramps in the wall. In Fig. 8, Hustrulid et al. gives the impression that the underground haul roads will be very close to each other. This is seldom the case. Figure 1 shows a haul road in the wall. The haul road passes through each cross-section only once. Ar¬ranging a reliable dewatering and rock support system from only one underground ramp is probably impossible. Many more drifts are therefore necessary. In our report, we also studied what would happen if the final pit slope is increased by 5°, using underground drifts in the wall. Our conclusion was that the extra cost for drifts, rock support, pumps, etc. destroys the whole idea, and that it was better to accept a higher stripping ratio with the haul road in the pit and to use conventional low-cost open pit equipment. Finally, we think it is would be difficult to try to reduce the safety factor when determining the slope angle by moving the haul road in the wall. Minimizing the risk for pit wall collapse is also important with in-the-wall haulage, primarily because men and equipment will be working in the pit, but also to guarantee many accesses between the pit and the haul road in the wall.

Jan 1, 1989

By F. D. Everett

This report, based on information made available by four uranium-producing companies, describes the geology, exploration, open-pit development and mining, and shaft sinking in the Gas Hills uranium district of Wyoming. Open-pit stripping features motor-scrapers push-loaded by crawler or rubber-tired tractors. The ground generally can be ripped, and little blasting is necessary. Detailed data are given on grouting for ground stabilization in sinking a small-diameter shaft in the relatively unconsolidated sandstone and siltstone, Cost and performance data are presented as made available by the companies.

Jan 1, 1963

By F. D. Everett

This report, based on information made available by four uranium-producing companies, describes the geology, exploration, open-pit development and mining, and shaft sinking in the Gas Hills uranium district of Wyoming. Open-pit stripping features motor-scrapers push-loaded by crawler or rubber-tired tractors. The ground generally can be ripped, and little blasting is necessary. Detailed data are given on grouting for ground stabilization in sinking a small-diameter shaft in the relatively unconsolidated sandstone and siltstone, Cost and performance data are presented as made available by the companies.

Jan 1, 1963

By J. J. Denny

IN November, 1932, an investigation of silicosis was undertaken at the Mcintyre Porcupine mine, Schumacher, Ont., after a discussion of the p"roblem with Sir Frederick Banting and his staff. As a result, it was decided to carry on dusting experiments with animals at the mine in a manner that would duplicate as far as possible actual industrial conditions. At that time 50 guinea pigs were placed in the crusher house tunnel of the mill where a considerable quantity of fine dust, containing approximately 35 per cent of free silica, was being constantly produced. These animals lived in this atmosphere for periods up to one year, and, while on autopsy large amounts of dust were found in the lungs, not a single case of silicosis had developed. These negative results suggested, among other things, that the mine gases might be a predisposing factor in the production of silicosis, and the results of this investigation (1) led us to undertake the study of the hydrogen-ion concentration of the condensate of the atmosphere, both in the mine and in various sections of the mill. The CO, combining power of blood serum on a series of 400 miners was also studied at this time. While these results were inconclusive, the variation in the hydrogen-ion concentration of the condensate between the surface and underground atmospheres encouraged us to investigate the effect of neutral, weak acid, and alkaline solutions on the solubility of siliceous materials. Gye and Purdy (2) were the first to point out that the chemical reaction, and not the physical presence of siliceous material, was responsible for the production of the fibrosis in silicosis. This work was investigated by Gardner and Cummings (3), who showed that the tissue reaction to quartz was definitely proportional to the size of the particle. They found that 1-3 micron particles of quartz produced an acute proliferative fibrotic response, while the 10-12 micron particles produced only a foreign-body reaction up to a period of three years. It is accepted that the dangerous silica particles retained by the lung are under 5 microns in diameter.

Jan 1, 1937

By Nathan C. Rockwood

WHILE mining engineers have been searching in far corners of the country and of the world for hidden wealth there has grown up around us in nearly every city great wealth-producing mines calling for the investment of hundreds of millions of dollars and yielding products now sold for over half a billion dollars yearly-largely unknown and almost wholly neglected by mining engineers. But this neglect is explainable and excusable. They are industries of very recent origin-practically the growth of the last 25 years. They are in a very large measure the result of tremendous developments in engineering construction and the rapidly expanding use of portland cement concrete for structures of every description. Concrete as a material of construction is going through an evolution very much as did cast iron and other metals used in engineering; and this phase of the industry should appeal to the imagination of metallurgical engineers. At first iron was iron-a material of uncertain properties, owing both to small differences in chemical composition and in methods of manufacture. By successive steps iron was studied and knowledge of its properties developed-the striking effects of very small percentages of other minerals and of various heat-treatments.

Jan 1, 1924

By Kirtley F. Mather

FROM almost every point of view, petroleum was "strategic mineral number one" during the World War that ended in 1945. Even the spectacular advent of the atomic bomb in the final days of the conflict did not displace it from its position of prime importance, although within a few years uranium will almost certainly be the "number one" material in the minds of military strategists, if it is not even now in that position. But both as fuel and as raw material for chemical industries, petroleum will hold the center of the stage for many years to come. Hardly any other substance illustrates so fully the manner in which science and technology may be combined to achieve the utmost success in contributing to human efficiency and comfort. Fundamental to any understanding of the problems implied by my topic

Jan 1, 1948

By Silvio Pereira Diniz Maranha, Evandro Costa e Silva

The disposal of coal tailings in an economically and environmentally sustainable way can be considered one of the biggest challenges for coal producers due to their physical, chemical and mineralogical characteristics and the significant annual volumes generated. The processing and utilization of coal fines is recognized as one of the great technical challenges of this industry. These challenges become even greater when it comes to the use of tailings from coking coals. This is due to the potential changes in their various properties, variability of these characteristics along the deposits, the handling and dewatering aspects of the products and the granulometric restrictions imposed by the coking plants for the coals to be handling and coking. This work presents the current stage of project development for the use of a metallurgical coal fines dam, addressing the general concept of the project, the exploratory sampling program and the characterization of the tailings for process and product development purposes after processing. It aims at the characterization and the carbonization tests for product development, the mining method considered, product alternatives, suitable to the market, to be generated and the next steps.

Oct 3, 2019

By C. E. Baltzer

This paper highlights the position of coal supply in regard to the requirements for electric-utility operations. The text and the appended tables outline the trend of thermal power development and fuel use in the electric-utility industry. Mention is made of several argumentative factors influencing the use of coal in relation to competitive oil and gas, and of the importance attached to developing a realistic understanding of the respective problems faced by the supplier and consumer of coal. * * * TREND OF" THERMAL POWER DEVELOPMENT T HE RATE OF ADVANCE in thermal power has been significant during recent years, particularly in the Atlantic Provinces, the Prairie Provinces, Ontario, and British Columbia. While dependence on thermal power in Quebec and the Northern Territories is less than in the remainder of Canada, these regions also eventually will have need for increased amounts of such power.

Jan 1, 1961

By A. Steiner, K. L. Komarek

Activities of aluminum in solid Ni-A1 alloys have been determined between 20 and 60 at. pet Al and 1200" and 1400°K by an isopiestic method in which nickel specimens, heated in a temperature gradient, are equilibrated with aluminum vabor in a closed all-alumina system. The activity of aluminum shows a strong negative deviation from Raoult's law at low concentrations but increases by three orders of magnitude within the ß(NiAl) phase. The partial molar enthalpy and entropy of mixing are negative. Using Wagner and Schottky's theory of ordered compounds, a degree of disorder of 4 x 10 -4 for NiAl and 1.25 X 10-2 for FeAl has been calculated THE Ni-A1 system has been studied by a great number of investigators, and the results, as far as the phase diagram is concerned, have been compiled by Hansen.1 The phase boundaries from 0 to 50 at. pet Ni are well-established. At higher nickel contents the boundaries are still in dispute and an additional phase, A12Ni3, has been reported.' The phase diagram is dominated by a very stable high-melting compound, NiA1, with a relatively wide range of homogeneity. Heats of formation of solid alloys have been determined calorimetrically by Oelsen and Middel3 from 20 to 95 at. pet Ni and by Kubaschewski4 from 25 to 80 at. pet Ni. According to the most recent compilation5 no other thermodynamic investigations have been reported for the Ni-A1 system. Due to the corrosive nature and the low vapor pressure of aluminum, a method has been employed for determining activities of aluminum which was previously developed for the Fe-A1 system.= Nickel specimens, heated in a closed evacuated alumina system in a temperature gradient, were equilibrated with aluminum vapor from a source within the system kept at constant temperature. After complete equilibration the specimens were analyzed and activities calculated from the known vapor pressure of aluminum. APPARATUS AND EXPERIMENTAL PROCEDURE Materials. The nickel specimens were made from wafers of electrolytic nickel (International Nickel Corp.) of 99.99 pet purity which were rolled to a 0.001-in.-thick foil by Driver-Harris Co. and to a 0.005-in.-thick sheet in our laboratory. The aluminum (Aluminum Corp. of America) had a purity of 99.99+ pct. The alumina tubes and crucibles were made of impervious recrystallized alumina with an alumina content of 99.7 pet (Triangle RR, Mor-ganite Inc.). Experimental Procedure. Annular specimens were punched from the sheet, the punching burrs removed, and the specimens degreased in carbon tetrachloride and acetone and weighed on a micro-balance to within an accuracy of ±0.01 mg. The specimens were positioned with alumina spacers along an alumina tube, and the positions measured. Aluminum metal was machined into cylindrical shape, and placed into an alumina crucible. The tube with the specimens was then inserted into a hole drilled into the aluminum metal. An alumina tube with its closed end at the top was slipped over the specimens so that its lower end fitted snugly into the alumina crucible. The assembled reaction tube was inserted into a mullite tube with a water-cooled brass head which had an opening for a quartz thermocouple protection tube and a metal-to-glass connection to a conventional vacuum system. A Pt-Pt 10 pet Rh thermocouple could be raised and lowered in the quartz tube which was placed along the outside of the alumina reaction tube. The mullite tube was heated by two separately controlled resistance-tube furnaces so that in the experimental temperature range an over-all temperature gradient of approximately 150o to 250°C could be imposed on the reaction tube. The position of the mullite tube was adjusted so that the surface of the aluminum metal was always at the temperature minimum. The reaction tube was thoroughly evacuated before and during slowly heating the assembly up to the melting point of aluminum. A pressure of less than 2 µ (Hg) was maintained during an experiment. Once the aluminum had melted, it isolated the contents of the alumina tube from the surroundings. Several times during an experiment the temperature gradient was carefully measured. An experiment lasted from 3 to 6 weeks and it was terminated by air cooling the evacuated mullite tube. For further details of the experimental procedure the paper on the Fe-A1 system6 should be consulted.

Jan 1, 1964

By J Hartnett, B Tarrant, A Rayner, D O’Toole, P Davies

Since 2009, the Northern Territory and Australian governments have been working under a national partnership arrangement to inform a rehabilitation plan for the former Rum Jungle uranium mine. Part of the rehabilitation strategy is to backfill a flooded former pit (Pit), which extends down to 100m below the current pit lake surface and was historically partially backfilled with uranium tailings. It is proposed to utilise the remaining pit volume below water level to sub-aqueously store Potentially Acid Forming (PAF-I) waste rock which currently occupies large stockpiles across the site. The rehabilitation design and planning process undertaken to develop a strategy commensurate to project objectives and construction constraints involved the establishment of key constraints derived from the analysis of historic data sources and preliminary design efforts. Tabled strategies were balanced against dependent project tasks and project objectives, especially surrounding minimising disturbance of highly contaminated materials within the Pit. Ideas were developed in conjunction with industry input and review of case histories to develop a remediation solution that is constructible within the project timeframe and constraints.

Jul 1, 2021

By A. Ghosh

Commonly used predictors of ground vibration from blasting, being linear in log-log plot, do not model the underlying physics of wave attenuation. Amplitude of the wave decays with distance due to geometrical spreading and inelastic attenuation producing a nonlinear carve in log-log scale. The nolinear decay of seismic waves has also been observed from non-explosive sources, such as, pile driving, drop hammer, traffic, etc. The improved predictors, by explicitly taking these two mechanisms into consideration, model the data trend extremely well at all distance ranges. Actual field data from different studies have been used to validate the improved models.

Jan 1, 1991

By H. Udin

G. KUCZYNSKI* and B. H. ALEXANDER*—This paper represents a most noteworthy attempt to evaluate experimentally the surface tension of a solid metal. Because of the great importance of such measurements, any proposed method should receive the closest scrutiny before the results can be considered reliable. In regard to the experimental method, we think that the marking of the gauge length by means of tieing knots in the wire may be the cause of some of the spread in the results. Such a knot may be expected to tighten slightly, and thus increase the gauge length, when placed under stress at high temperature. Although this effect would be very small, amounting at most to only a few times the wire diameter. A fairly tight knot in a wire will decrease the wire length by about ten times the wire diameter, thus only a slight tightening of the knot would cause considerable spread in the results. Upon plotting the stress strain curves from the authors' data, the writers found that there was a fairly consistent tendency towards an S-shaped curve, instead of a straight line. Such an effect could be caused by the tightening of the knots. The writers think, however, that the experimental results are fairly reliable, but that there may be other methods of interpreting them depending upon what mechanism is assumed to be responsible for the shrinkage of the wires. The authors have assumed that the stress due to surface tension results in viscous flow. It should be made clear that it has never been demonstrated that viscous flow can occur in metal crystals even at very high temperatures. The experiments of Chalmers13 on tin, which are so frequently quoted as giving evidence of viscous flow at low stresses are by no means satisfactory. In his experiments, Chalmers found that only the initial rate of flow was approximately proportional to stress. He also found that the rate of flow varied markedly with time which, in his experiments, was less than 2 hr. Inasmuch as there is no proof of viscous flow in metals, and the authors have brought forth no conclusive evidence on this point, it may be worth while to investigate other possible mechanisms of material transport which would account for the shrinkage of the wires. The writers wish to point out that in these experiments the shrinkage of the wires can be adequately explained, according to a self diffusion mechanism. Thus, if we assume a concentration gradient for self diffusion which is a function of the radius of curvature of the wires, and assume that diffusion will occur so that the total surface area is decreased, we find the following expression for the self diffusion coefficient: where k = Boltzmann constant r0 = initial radius of the wire T = absolute temperature ? = surface energy 8 = interatomic spacing t = time e = strain at zero applied stress Eq 19 may be used to evaluate the self diffusion coefficient of copper, using the strain measurements obtained by the authors for zero stress as obtained by extrapolating their curves for 5 rail wires. By inserting a reasonable value for the surface energy (1500 ergs per cm2) we find: -66,000 D = 5 X 10e RT [20] The activation energy is of the correct order of magnitude, but the frequency coefficient is much too high, indicating that surface diffusion may be playing an important role. This discrepancy in the action constant is much smaller than the corresponding discrepancy obtained by the authors for the viscosity coefficient. The writers by no means propose that this proves that the shrinkage of the wires is due to self diffusion but we merely wish to point out that there are explanations other than that given by the authors. In this, as in any kinetic phenomena, it is necessary to study the rate of the process before anything can be said about the mechanism. The determination of surface tension given by the authors is based upon an interpretation of the data which embody the concept of viscous flow. The final proof of this concept will be obtained only after the time relationships confirming the authors' Eq 15 have been conclusively established. The rough linearity of the stress strain curves obtained by the authors for experiments run the same length of time should not be considered as proving that viscous flow is occurring. H. UDIN (authors' reply)—All of the test specimens were annealed at 1000°C for an hour or more before preliminary measurements were made. During this anneal the wires recrystallize, and the greatest part of grain growth takes place. Also, the knots sinter at the cross-over points. This does not in itself eliminate the possibility of end errors, although it greatly decreases their probable magnitude. It is still possible that some extension occurs due to creep in shear at the sintered points. If so, this effect would be quite independent of and superimposed on the normal shrinkage or extension of the wire itself. Within the precision of the experimental results, straight lines satisfy the data as well as do any other simple curves. Until data of greater precision are obtained, it is futile to discuss any possible trends away from linearity. The disagreement between Kuczynski and Alexander's Eq 19 and our Eq 18 is one of semantics and mathematics, not mechanism of flow, since Eq 18 is based on the self-diffusion concept of viscous flow. It would be interesting to learn how the mathematics leading to Eq 19 deviates from that of Eyring and of

Jan 1, 1950