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THE slag from the blast furnaces having been granulated, a representative sample is taken to the sample mill. It is then dried, crushed through a 100-mesh screen, intimately mixed, and packeted for assay purposes.METHOD OF ANALYSISINSOLUBLEWeigh 1 grm. of the finely-pulverized slag into a 3t-in. casserole, moisten with a little water to prevent sticking, cover with a clock glass, and add 20 cc. of hot acid (1 HNOs, 3 HCI, 4 H2 0). Evaporate slowly to dryness on a hot plate and bake (without overheating) until all the gelatinous silica is dehydrated. Cool, add 20 cc. HCI (1-1), and boil gently for several minutes; filter into a 300-cc. beaker, cleaning out the casserole thoroughly with a rubber-tipped glass rod. Wash residue with hot distilled water and transfer it to a No. 1 porcelain crucible. Dry, ignite, cool in a desiccator and weigh as total insoluble matter. Dilute filtrate to 200 cc. and neutralize some of the excess HCI with NHa.OH. Warm, and pass H2S for 15 min. Filter and wash withhot water. Boil off H2 S, oxidize with 5 cc. HNOll , reduce bulk of the solution by evaporation. to about 100 cc., and transfer to a 250 cc. flask.SILICAFuse insoluble residue over a blast lamp in a platinum crucible with three or four times its weight of anhydrous carbonate of soda, for 10 to 15 minutes, or until decomposition is complete. Cool, and extract fusion in an 8-in. evaporating dish with HCI (1-1); rinse crucible and cover with distilled water, and evaporate to dryness over a water bath. Take up dry mass with 10 cc. strong HCI, and then.

Jan 1, 1922

By Donald Markle

Anthracoal is a mixture of small particles of anthracite coal and a matrix of practically pure carbon, formed from the distillation of coal-tar pitch or other suitable bitumen. It is a hard, dense, homogeneous mass, with a silvery luster and in color varies from silvery to grayish black. When pushed from the oven, it develops only partly the fingerlike structure of coke; but, unlike coke, it has a tendency to remain in blocky masses. When struck with a hammer or passed through crushing rolls, it breaks with an irregular fracture, similar to anthracite, but with very little fines. Due to its density, anthracoal is harder, tougher, and stronger than coke. The results of a test made by the blast-furnace department, of the Bethlehem Steel Co., on two barrels of anthracoal are given in Table 1.

Jan 1, 1922

By R. Van A. Mills

[In previous contributions** the writer has called attention to important relations that faulting bears to the migration and accumulation of oil end gas. It has been pointed that favorably situated parts of oil and gas bearing, sands have been enriched by migration art segregation incident to faulting. The escape of water through natural passages such. as fault fissures has induced wide spread hydraulic currents through the beds toward these, points, of diminished pressure and these water currents, plus buoyancy hove contributed largely toward the migration of oil to favorable rock entrapments in the vicinity of the faults.*** The propulsive force of expanding gas has been one of the contributing causes for the hydraulic currents. Paradoxical as it may seem, the escape of gas with entrained oil through fissures has been on important factor In the migration, and accumulation of oil in many faulted areas. Compressed gas is the propulsive force by which oil generally moves to producing wells. It is also one of the propulsive forces by which oil has moved with or even ahead of water under conditions: of differential pressure brought about by faulting.]

Jan 1, 1922

By William E. Ford, Edward Salisbury Dana

1. Normal Class (28) Gypsum Type 2. Hemimorphic Class (29) Tartaric Acid Type 3. Clinohedral Class (30) Clinohedrite Type Mathematical Relations of the Monoclinic System Crystallographic Axes. - The monoetinic system includes all the forms which are referred to three unequal axes, having one of their axial inclinations oblique. The axes are designated as follows : the inclined or clino-axis is a; the ortho-axis is b, the vertical axis is c. The acute angle between the axes a and c is represented by the letter 0; the angles between a and b and b and c are right angles. See Fig. 331.

Jan 1, 1922

By R. J. Wensley

The use of small substations for the supplying of 275-volt energy to the locomotive and cutting machines in coal mines is a well-established practice. A few years ago, when labor costs were lower, these substations were located as near to the load as possible, and an operator was provided for each station. This practice has now become so expensive that substations are being located with reference to other mining machinery, such as hoists or pumps, so that one operator can look after both. Sometimes the substation is operated by one whose duties make him traverse quite a large area. In such cases the interruption of alternating-current supply may produce a long interruption in the direct current, as the station cannot resume service until this man reaches it. Such interruptions interfere seriously with production and may easily counterbalance the supposed saving gained by such operating methods. The grouping of substations for convenience in operating may also result in excessive copper loss and consequently poor trolley voltage, with its attendant evils of low locomotive speeds and increased locomotive motor maintenance. The speed of the coal-cutting machines will also be reduced. By relieving the substation of its burden of the operating labor cost, the most economical location, from an electrical standpoint, may be chosen. The matter of machine insurance should also be considered. If an attendant is caring for several kinds of equipment, he cannot watch the machine continually for signs of trouble; therefore, continued overload, phase failure, low alternating-current voltage, bearing trouble, etc. may result. Some partly automatic equipments have been installed; these have protection against low voltage, reverse current, and bearing trouble and are provided with automatic reclosing circuit breakers. This is a step in the right direction but it does not go far enough to give first-class machine insurance. The saving in maintenance costs is often the smallest item, when considering the automatic substation as machine insurance. When the coils in a machine are roasted out, due to continued overload or to opera-

Jan 1, 1922

By John A. Mathews

During the prosecution of the aircraft-production program in 1917 and 1918, the writer visited many plants engaged in the manufacture of motors, planes and parts, in carrying out his duties as chairman of the Committee on Aircraft-engine Forgings. On several occasions, when the question of expansion was discussed, it was noted that there was confusion in the use of the terms: the true coefficient of expansion, a physical constant, and distortion in hardening. One engineer, referring to a steel shown in the accompanying table, stated that he could not consider it for crankshafts because of its excessive coefficient of expansion, while another steel, also Iisted in the table, was said to be especially good because it had no coefficient of expansion, since it came out of the oil bath perfectly straight. Many years ago one of our employees designed a new oil furnace; when asked what became of the products of combustion, he replied: "There ain't any, we burn them all up." While the coefficient of expansion is not without its effect in volume changes in hardened steel, it is not a determining factor in the matter of distortion and going out of shape. Irregular heating, uneven furnace bottoms, and carelessness in withdrawing the part from the furnace, as well as the manner in which the part enters the quenching bath are of greater moment. Generally speaking, also, steels of relatively low hardening temperature will distort less than those requiring higher hardening heats. The coefficient of expansion must be considered in engineering design most frequently when different metals or alloys are used in the same construction. For example, the difference of expansion between a steel crankshaft and an aluminum crank case might be of real importance and a steel with no coefficient of expansion would be much less desirable than one with the normal coefficient. About 15 years ago, the writer made many determinations of the coefficient of expansion at low temperature ranges, usually between 20' and 100" C. Among the materials tested were: Pure forged electrolytic iron, 11.73 parts per million for l° C.; cast aluminum (99.93 per cent. AI.),

Jan 1, 1922

By William E. Ford, Edward Salisbury Dana

5. Crystallography. - The subject of Crystallography includes the description of the characters of crystals in general; of the various forms of crystals and their division into classes and systems; of the methods of studying crystals, including the determination of the mathematical relations of their faces, and the measurement of the angles between them; finally, a description of compound or twin crystals, of irregularities in crystals, of crystal- line aggregates, and of pseudomorphous crystals. 6. Definition of a Crystal.- A crystal * is the regular polyhedral form, bounded by smooth surfaces, which is assumed by a chemical compound, under the action of its intermolecular forces, when passing, under suitable conditions, from the state of a liquid or gas to that of a solid. As expressed in the foregoing definition, a crystal is characterized, first, by its definite internal molecular structure, and, second, by its external form. A crystal is the normal form of a mineral species, as of all solid chemical com- pounds; but the conditions suitable for the formation of a crystal of ideal perfection in symmetry of form and smoothness of surface are never fully realized. Further, many species usually occur not in distinct crystals, but in massive form, and in some exceptional cases the definite molecular structure is absent. 7. Molecular Structure in General.- By definite molecular structure is meant the special arrangement which the physical units, called molecules, assume under the action of the forces exerted between them during the formation of the solid. Some remarks are given in a later article (p. 22 et seq.) in regard to the kinds of molecular arrangement theoretically possible, and their relation to the symmetry of the different systems and classes of crystals.

Jan 1, 1922

By J. J. Jakowsky

[The legislation in many States against the present method of producing carbon-black by the incomplete combustion of natural gas, and the continually increasing demand for gas for otter purposes, indicates that the supply of carbon-black may Gradually be decreased and that new methods for its production, utilizing a greater parentage of the carbon in the has should be developed. In the course of investigations of the effects on hydrocarbons of high voltage discharges, it was noted that under certain conditions natural gas could be decomposed and that carbon-black could be produced. The effects of several tyres of electrical discharges on natural gas have, accordingly, been studied' in order to find out the fundamental factors underlying the reactions and their possible influence in the recovery of a greater part of the carbon content of natural gas than is now possible. Present commercial plants using natural gas for the manufacture of carbon-black recover from 0.9 to 1.5 pounds of carbon-black per thousand cubic feet of gala consumed, or less than 5 per cent of the total Gabon in the gas: It should be noted, however, that the, present methods involve heating the gas to incandescense by burning it as a luminous flame, and a considerable part of the gas is thus consumed as a source of hest. If this heat can be supplied from some other source, or if a more efficient method of applying the energy con. tamed in part of the gas, to the decomposition of the rest of it, can be worked out, then a greater yield of carbon-black per thousand cubic feet of gas care be expected. The present abort paper contains a brief summary of tie investigations so far conducted upon natural gas.]

Jan 1, 1922

By A. C. Watts

The question of disposition of the slack and dust so troublesome to coal mine operators of the West has been divided by your committee chairman into three heads, viz: The preparation and transportation of fine and powdered coal. The developments along the line of low heat carbonization. The uses to which fine and pulverized coal have been put. The development of low heat carbonization has been assigned to me. This is really not a part of the subject but as it has a most important bearing on the future use of coal, I presume the chairman thought best to include it. An English committee on smoke abatement makes the statement that the burning of raw coal is "dirty, wasteful and unscientific". I will go a step further and characterize it as an "economic crime." It has been predicted by eminent scientific men that eventually no raw coal will be burned for heat or power purposes. All this will take time, experimentation and large expenditure, but it will surely come. The question of disposition of slack and dust so troublesome to coal and utilization of its by-products has been retarded by the abundance and cheapness of the raw coal, and by the abundance of suitable coking coals for metallurgical purposes. But necessity is surely, if slowly, demanding that the enormous waste ensuing from the burning of raw coal for heat and power must cease. For instance, smoke abatement investigations in Manchester, England, showed that the increased cost of household washing was about $1,250,000 per year due to smoke and soot. It is estimated that in London 200 tons of soot and smoke particles are suspended in the atmosphere over that city during dense fogs and that much more than this is emitted from the chimneys each winter day during the forenoon. As an example of what benefits a smokeless fuel gives, it is cited that in the mill town of Shaw, England, the burning of smokeless fuels in the factories has reduced the so-called fogs by about 80%. Necessity, caused by the war led Germany into the field of low tem¬perature carbonization because of the shortage of motor fuel and lubricating

Jan 1, 1922

By H. F. Nash

Coal is the basic necessity of our present-day civilization, and those engaged in the industry, whether miner, day-man, pit boss, tipple boss, superintendent, salesman or operator, have a direct responsibility to the public at large. Our country is blessed with a great supply of Bituminous coal, upon which it must largely depend for its industrial prosperity. Anthracite coal, in its relation to our economic situation, is a small factor, as its ratio of production to Bituminous coal is only about one-sixth. However, within the last ten years, electricity and oil have largely displaced the use of coal in industry, so that the use of Bituminous coal is decreasing, relatively, and the potential production of Bituminous coal has largely increased since the war. High wage scales and high freight rates make the delivered price of coal to the consumer so out of proportion to the cost of electricity and oil -and strikes make the supply of coal so uncertain-that industry is rapidly turning to electricity and oil. The energy in a ton of coal can be transported, by electric current, a distance of 250 miles for 78% of what it costs to ship the coal in bulk, by rail, in the East-and, for about 60% of what it costs in our section of the country. The use of fuel oil, distillate and gasoline, in industry, has increased by leaps and bounds. Especially was this noticeable during the strike this year, as the large packing plants in Kansas City, Omaha and Sioux City (that formerly used nothing but coal) are now practically all using oil. This also supplies to other industrial plants throughout our territory in Texas, Oklahoma, Kansas and Nebraska. Many railroads are using oil, as are also the smelters, cement plants, etc., etc. Ten years ago, 100% of the threshing in the state of Kansas was done with coal-today not over 25% of it is done through that means-and so it goes all along the line. The use of our coal is being yearly more restricted in industry. In the case of domestic consumption, the circle is also ever decreasing.' In small towns and on farms, kerosene, gasoline and wood are largely utilized for cooking. For the past four years, along any country road, it is a common occurrence to hear a buzz-saw cutting old fence posts or timbers taken from creek bottoms. Many thousands of tons of coal are displaced each year through the use of corn and cobs. In larger towns, gas plants have been installed, and many housewives use gas-in communities contiguous to natural gas, that is used for industrial and domestic purposes. The time has gone when industrial and domestic consumers or dealers are satisfied to buy anything that is black-competition among the coal-producing states is keen, and will become more so. Eastern and southern fields are turning out splendidly prepared coals of high quality, and with their lower freight rates to competitive territory, will entirely nullify the use. of our Western coal unless-

Jan 1, 1922

By P. A. E. Armstrong

For hardening, the steel should be heated just above the critical temperature, as a properly forged steel quenched from this heat has some toughness, with maximum hardness and density. The quenching bath should be kept at approximately a constant temperature. In drawing or tempering, longer time periods at lower temperatures are better than the shorter periods at higher temperatures. A recent questionnaire brought out the following facts: The double-arc, double-taper bit and cross bit give the best service; resharpening of the drill steels most frequently was caused by wear of gage; chipping of bit was, with one exception, the second cause; breakage of shank was with one exception, the third cause; upsetting of bit, upsetting of shank, and breakage of body were the fourth cause. The direct cause of the necessity of resharpening given was poor heat treatment first, and faulty steel and severe rock conditions second. Rock-drill Steel By N. B. Hoffman Much of the drill steel produced in America is manufactured into hollow rods. After all forging has been finished the entire bar should be thoroughly annealed and heat trcated before the point is hardened and tempered, at least where the drill has heavy duty, such as working in deep holes and hard rock. A large number of tools of like character and doing work requiring similar properties are now being made of alloy steels; for instance a steel with a carbon content of 0.75 to 0.85 per cent., manganese 0.25 to 0.35, phosphorus under 0.020, sulfur under 0.030 and vanadium 0.18 to 0.23 has proved very satisfactory for chisels. A steel of this type properly manufactured will be far superior to the ordinary carbon steels, while at the same time is one whose price range should not prove prohibitive. Much of the cutting efficiency of a drill depends on proper heat treatment. This vanadium steel has a far greater safe hardening and forging range than ordinary carbon steels, making it more nearly foolproof. It will harden nicely at 1400" I?. but will also harden well and satisfactorily at 1550" F. retaining its quality of hardness and toughness in either case. Drill Steel from Hollow Ingots BY P. A. E. ARmstrong Hollow drill steel is made from a drilled billet with a sand-filled core or the drilled, pierced, or the drilled and pierced billet, not sand-filled, is rolled down over a projectile or ball much the same as in ordinary pipe manufacture. The first is the method generally used in this country; the second is used largely in Sweden. Swedish hollow drill steel has a

Jan 1, 1922

By Dever C. Ashmead

Anthracite was first mined in the Wyoming Valley and sold as an article of commerce in 1808. As some preparation has always been necessary to make it ready to burn, the preparation of anthracite must date back over a hundred years. Two vital factors have determined to a large extent the degree and the method of anthracite preparation. These are, first, the character of the beds worked and the methods by which they are mined and, second, the equipment used and practices followed in the burning of the coal. It is not the intention here to go deeply into these phases of preparation as a paper of no mean length could be prepared on the history of either. Rather, the intention here is to point out the main considerations and to show the influence they have exerted on the preparation of anthracitc. Mining Methods and Their Relation to Preparation In the beginning of the nineteenth century, the coal beds were virgin with the possible exception of some outcroppings that had been worked, to a slight extent, by the Indians. It is known that the American aborigines had a, knowledge of the use of this fuel, because when the Wyoming Valley was purchased from them, in 1754, they mentioned the fact that, by selling the land, they would lose their coal. Real mining of anthracite began about 1808 when Judge Jesse Fell, of Wilkes-Barre, discovered that the "common stone coal of the valley" could be burned in an open grate. For some years thereafter mining was conducted near the surface. The working p1aces were driven narrow; only the best of the coal was selected and the remainder was left in the ground. Only the lumps could be used, as no market existed for other sizes. As time passed, however, it became necessary either to go farther into the ground or to widen the working places. When these places were widened, falls of roof were apt to occur, making it necessary

Jan 1, 1922

By D. H. Newland

Certain observations from the field and laboratory suggest the need for recasting some of our ideas about gypsum as a rock-forming mineral and in relation to supplies for industrial use. Until about 25 years ago, the use of gypsum was confined almost entirely to agriculture. During the past quarter century, though, its usefulness has been greatly developed, particularly in the building trades, which now absorb most of the gypsum produced. In 1919, according to the U. S. Geological Survey, the output of crude gypsum was 2,240,163 tons, a gain of 912 per cent. in 25 years. About one-half of this production was mined in New York, Ohio, and Michigan, where the proved supplies can hardly be regarded as over-large when viewed in relation to the rapid expansion of industrial requirements. The occurrence of gypsum in the United States is treated by R. W. Stone and others.' The deposits of Canada are described by L. H. Cole. Several states, including Kansas, Oklahoma, Iowa, Michigan,and New York, have made special surveys of their gypsum deposits, but the reports, as a rule, refer to conditions as they existed from 15 to 20 years ago. Association of Gypsum and Anhydrite The two calcium sulfate compounds, gypsum (CaSO4.2H2O) and anhydrite (CaS04), are the more stable forms of a series which includes at least two other members, so-called half-hydrate (CaSO4.1/2H20) and soluble anhydrite (CaS04). Each of the latter readily takes up water to recrystallize as gypsum and consequently is incapable of existence under ordinary geological conditions; also each can be prepared from gypsum by the application of heat within certain temperatures, the process on which is based the manufacture of commercial plasters. If the temperature limitations are not observed, the result of the calcination process will be insoluble anhydrite which, compared with the soluble form, takes up water very slowly so as to be of no practical use, although actually it is soluble and in time is convertible into gypsum like the other forms.

Jan 1, 1922

By William E. Ford, Edward Salisbury Dana

General Principles of Optics Optical Instruments and Methods General Optical Characters of Minerals 1. Diaphaneity 2. Color 3. Luster Special Optical Characters of Minerals belonging to the different Systems A. Isometric Crystals B. Uniaxial Crystals General Optical Relations Optical Examination of Uniaxial Crystals C. Biaxial Crystals General Optical Relations Optical Examination of Biaxial Crystals 306. Before considering the optical characters of minerals in general, and more particularly those that belong to the crystals of the different systems, it is desirable to review briefly some of the more important principles of optics upon which the phenomena in question depend. For a fuller discussion of the o tics of crystals, special reference is made to the works of Groth (translation by Jackson), Liebisch, Mallard, Duparc and Pearce, Rosenbusch (translation by Iddings), Iddings, Johannsen, Winchell, mentioned on p. 3 also to the various advanced text-goks of Physics. 307. The Nature of Light. - Light is now considered to be an electro- magnetic phenomenon due to a periodic/variation in the energy given off by vibrating electrons. This energy is transmitted by a series of periodic changes that show all the characters of ordinary wave phenomena. The light waves, as they are commonly called, possess certain short wave-lengths that are of the correct magnitude to affect the optic nerves. Other similar waves with longer or shorter wave-lengths belong to the same class of phenomena. Immediately beyond the violet end of the visible spectrum come the so-called "ultra- violet" waves with still shorter wave-lengths and on beyond these we have the X-rays and the "gamma" rays produced by radium. Of the waves having greater lengths than those of light waves we have the waves that give

Jan 1, 1922

By N. A. C. Smith

One of the most important considerations in any manufacturing industry is the production of stable material, that is, material which will not change in quality before it reaches the consumer. The manufacturer of gasoline, the refiner of crude petroleum, is handicapped in this respect by the varying nature of his raw material, but as far as it is commercially practicable, he has endeavored to improve his product, and in most cases he has been eminently successful. It sometimes happens, however, that a gasoline that is apparently normal when first made, will In time deposit small quantities of a gummy substance. The present Investigation was undertaken in the hope that it would throw some light on these gums and indicate how their formation might be prevented.

Jan 1, 1922

By R. S. Reed, D. L. Ward

This paper is the result of a study, in 1919, to determine how much surplus power could be produced through the proper utilization of the entire gas flow from the two furnace stacks at the Federal Furnace Plant, South Chicago, 111. Obviously, the problem was to measure the flow of gas through the main beyond the point where the amount necessary for stove operation mas rermoved. In all probability, blast-furnace gas is the most difficult gas to measure, because of the high moisture and dust content, and the widely fluctuating flow from the furnaces. This wide fluctuation of flow forbids the acceptance of any one group of flow road-ings as indicative of normal operating conditions. A study of the conditions showed that a recording device on gas flow was necessary. As the gas at the point of measurement had passed through met washers, and accordingly was saturated with water and contained considerable dust carried past the scrubbers in the form of sludge, no form of Pitot tube could be used, for this sludge would quickly plug the dynamic. and static holes, spoiling the gage readings. An even more serious objection to the use of Pitot tubes was the impossibility of accurately measuring the cross-sectional area of the gas main on the plane of Pitot-tube installation. Given an absolutely clean gas and a perfectly circular pipe, it would be safe to assume, through measurements of the pipe diameter, that the gas main was of a certain cross-sectional area. But the continual depositing of sludge and the fact that the main mas fabricated from riveted sheets led us to discard the idea of using Pitot tubes for. this service. The Venturi tube mas then considered, and had there been a sufficiently long straight run of gas main to accommodate a tube of the required size (72 by 28 in.) such an installation would very likely have been made. A plate with a sharp-edged orifice was eventually accepted as it possesses all the characteristics of a Venturi tube, requires less space, and

Jan 1, 1922

By H. DeWitt Smith, W. H. Sirdevan

The mine operated by the United Verde Copper Co. is situated near Jerome, Ariz., on the eastern flank of the Black Hills, at an elevation of approximately 5500 ft. (1676 m.) above sea level. The mine and the town of Jerome are located on a steep hillside, which slopes rapidly to the valley of the Verde River. The smelter town of Clarkdale is situated in the Verde valley 4.1 mi. (6.5 km.) distant in an air line from Jerome, and at an elevation of 3560 ft. The two towns are connected by the standard-gage railroad of the Verde Tunnel & Smelter R. R., a subsidiary of the United Verde Copper Co. This road is 11 mi. long and has a compensated 4 per cent. grade. At Clarkdale, it connects with the Verde Valley branch of the Santa Fe R. R. The narrow-gage (36-in.) line of the United Verde & Pacific Ry. was, until 1919, Jerome's only rail connection with a main trunk line. This road connects with a branch line of the Santa Fe system at Jerome Junction, after traversing 26 mi. of mountainous country. From the time of its location, in 1876, until its purchase by Senator W. A. Clark, of Montana, in 1889, the United Verde mine was worked on a small scale and shipments of high-grade gold-silver ore were made from the surface workings. Until 1894, when the narrow-gage railroad to Jerome Junction was completed, all supplies for the mine and smelter

Jan 1, 1922

By Howard Scott

The great advances made in mechanical engineering during recent years through the use of alloy steels, as illustrated by the development of the airplane and automobile, may be ascribed primarily to the application of nickel as an alloying element. The ternary system iron-carbon-nickel has a wide industrial application and forms, further, thefundamental basis of the even greater class of the widely used quarternary steels such as nickel-chromium, nickel-silicon, and nickel-vanadium. As is not uncommon with such cases of virile growth in an industry, the application of the alloy steel in a largely empirical manner has outstripped its scientific development so that a fertile field for metallographic research still remains. In this field, the basic nickel steels require first consideration and are the subject of the present investigation, which is offered as a preliminary to the study of the more complex alloys of industrial importance Of the principal tools of metallography—microscopic examination, determination of mechanical properties, and thermal analysis—the last has developed much more slowly in its application to industrial needs so that the situation often exists that heat treatment operations are based on empirically determined temperatures; that is, temperatures deterrnincd without regard to the actual transformation characteristics of the alloy. This situation is undesirable as there is no uniform standard for comparison of results. It is due, outside the usual difficulties involved in temperature measurements, to the pioneer character of much of the published work; to the lack of definiteness of the Ac, transformation,1 particularly in low-carbon steels; to the failure to define operating conditions completely; and to the paucity of information correlating thermal characteristics with results of heat treatment.

Jan 1, 1922

By William E. Ford, Edward Salisbury Dana

1. Normal Class (25) Barite Type 2. Hemimorphic Class (26) Calamine Type 3. Sphenoidal Class (27) Epsomite Type Mathematical Relations of the Orthorhombic System Crystallographic Axes. - The orthmhombic system includes all the forms which are referred to three axes at right angles to each other, all of different lengths. 296 Any one of the three axes may be taken as the vertical axis, c. Of the two horizontal axes the longer is always taken as the b or macro-axis * and when orientated is parallel to the observer. The a or brachy-axis is the shorter of the two horizontal axes and is perpendicular to the observer. The length of the b axis is taken as unity and the lengths of the other axes are expressed in terms of it. The axial ratio for barite, for instance, is a : b : c = 0'815 : 10 : 131. Fig. 296 shows the crystallographic axes for barite.

Jan 1, 1922

By William E. Ford

The first edition of this book appeared in 1877 and approximately twenty years later (1898) the second and revised edition was published. Now, again after more than twenty years, comes the third edition. The changes involved in the present edition are chiefly those of addition, the general character and form of the book having been retained unchanged. In the section on Crystallography the important change consists in the introduction of the methods employed in the use of the stereographic and gnomonic pro¬jections. A considerable portion of the section on the Optical Characters of Minerals has been rewritten in the endeavor to make this portion of the book simpler and more readily understood by the student. In the section on Descriptive Mineralogy all species described since the previous edition have been briefly mentioned in their proper places. Numerous other changes and corrections have, of course, been made in order to embody the results of mineral investigation during the last two decades. Only minor changes have been made in the order of classification of the mineral species. It was felt that as this book is so closely related to the System of Mineralogy it was unwise to attempt any revision of the chemical classification until a new edition of that work should appear. The description of the methods of Crystal Drawing given in Appendix A has been largely rewritten. A new table has been added to Appendix B in which the minerals have been grouped into lists according to their important basic elements. Throughout the book the endeavor has been to present in a clear and concise way all the information needed by the elementary and advanced student of the science. The editor of this edition is indebted especially to the published and un¬published writings of the late Professor Samuel L. Penfield for much ma¬terial and many figures that have been used in the sections of Crystallog¬raphy and The Optical Character of Minerals. He also acknowledges the cordial support and constant assistance given him by Professor Edward S. Dana.

Jan 1, 1922