the Continent, and it would be of great interest to know to what extent the process had been used during and since the war in Germany and other foreign countries. Apparently the industry was in its infancy in this country. He was anxious to know whether anything had been done to apply the process to the drying of peat. It was a very important question at the present time, because of the great shortage of fuel. In some Continental countries, notably Italy, lignite and peat deposits could be very well utilised if they were amenable to that sort of treatment. In the chemical industry of nearly every country there were certain by products and factory wastes which were to some extent of the colloidal nature, and those products very often contained material which, if it could be sufficiently recovered, would yield a very handsome profit. One of the commonest instances was perhaps sewage, in connection with which considerable use had been made of centrifugal machines and filters. It would be interesting to know how the osmosis process would compare with other methods that were used, and to have some idea of what the cost of treating the clays was, in order to have a comparative basis in considering the problems. There was also the question of the conditions under which various bodies were capable of undergoing osmosis treatment. The authors had dealt almost entirely with suspensions in water, and he would like to know whether the process was at all applicable to materials suspended in other liquids, such as ferric hydrate in a caustic soda solution or arsenical suspensions in sulphuric acid. noticed that the clay separated out very rapidly, and he would like to know what the weight of separation was, and whether it varied to any considerable extent with different materials. At the present time considerable interest was being taken in the question of suspension of coal dust and other combustible material in oil, to which the generic name of "colloidal fuel" had been given and it occurred to him that possibly investigation into the time required for the separation might be a useful method of determining the efficiency of those suspensions in oil.

He

Dr. W. R. ORMANDY, in replying to the discussion, said a very fine piece of work was involved in the coloured photographs which necessitated Mr. Northall-Laurie working very late hours, as even the vibration of passing traffic would ruin the photographs altogether. With reference to the remarks of Sir Herbert Jackson, an osmosed clay muffle, made from a certain clay, lasted thirteen journeys, heated up to 1500° C., as shown by the pyrometer, whereas muffles made from the same clay used by the muffle maker without treatment would never last three journeys. Taking the finest English china-clay which had been treated with 97 tons of water in order to wash 3 tons of clay, it was still possible to separate from that clay 7 per cent by weight of a product which consisted almost entirely of silica and mica and large rouleaux of china clay, which were not broken up or dispersed by the alkali. Mr. Hancock had rather emphasised the point raised by Sir Herbert Jackson that in the manufacture of optical glass there was a great demand for higher grade | refractories than were available previously. That was not only due to the mechanical properties of the clay, but for optical purposes it was essential

With

that the clay substance itself should not enter into the mixture in a pot to any appreciable extent. As most fireclays contained a good deal of iron, iron, which was a colouring matter, was introduced. Therefore, for the optical glass maker, it was essential that he should have a crucible which would stand the high temperature and would not be eaten away by the corrosive action of the products which were being melted. In the manufacture of ordinary commercial glass there was a very great opening for the use of clay treated by the osmosis process, because at the present moment the great glass industries of this country, which were being developed to a degree unknown before the war, were severely handicapped by the kind of clay they had to employ for their tank blocks and for making crucibles. There was no question that an osmosed clay, owing to its refractory properties, would resist the corrosive action of the fluid glass in the tank. In the past manufacturers on the Continent had made great progress in the manufacture of glass, and if this country was to gain the industry to supply not only our own requirements but the world's markets, it would be necessary to recognise that the methods that were used by the Egyptians were still largely in use to-day, and were methods that had to be scrapped. It was no use stating that science was a great thing unless the manufacturer was going to support science and apply it. regard to Mr. Patchell's remarks, many people had the idea that the straw used in Egypt was mixed into the bricks in the form of a binder, but that was not the case. The Egyptians used to put the straw into tanks and allow it to ferment in a hot climate until it went into a colloidal rotting mass, and that was used to mix with the sandy Nile-clay in order to make it more plastic. The lack of demand in this country for purified osmosed china-clay in the early days merely showed that the users were not sufficiently educated to realise that it paid to use a scientifically purified product. The manufacturers had to be educated, and to a very large extent the directors of some of the big companies needed education. With regard to Captain Goodwin's remarks, the osmosis process was derived primarily from the Continent, where there had been a greater time to develop it. In Austria there were already china-clay works turning out 60 or 70 tons a day, and there were works at Klingerberg being worked by the process, and very large works with seven or eight machines near Coblenz, and plant was already being erected in Spain. With reference to the drying of peat, that was a subject that had occupied his and his colleague's attention very considerably. The osmose filter press was, in his opinion, the only method which had yet been offered that showed a possible outlet for the treatment on a commercial scale of colloidal peats, which could neither be centrifuged nor pressed. Unfortunately the bulk of peat in the world was of a colloidal type. Such peat could be treated by the osmosis process, and he thought no long time would elapse before Mr. Highfield would be in a position to deal with the matter in another paper. Sewage experiments had also been carried out. One of the troubles was that, whereas clay would travel from one pole definitely to the other, in sewage there was a heterogeneous mass material, some of which went to one pole and

of

some to another, and some had no electrical property whatever and would not move. As far as his own experiments went, there did not appear to be any immediate prospect of the electrical treatment of sewage proving any solution of the difficulty. As to the conditions of use, it was quite obvious that a particle could not move in an electric field if there was a good deal of soluble salts present, and that ruled out the possibility of separating colloidal ferric hydrate from a caustic soda solution, as the soda would convey the current and a very large amount of electricity would have to be used. The only way in which colloids suspended in an electrolyte could be dealt with would be to use a modification of the process. First of all, the electrolytic salts should be removed from the solution, leaving the colloid in a watery solution, and afterwards it could be dealt with in the same way as clay. With regard to the rate of output, that was conditioned to a certain extent by the electric pressure used, but there was an economical rate which it did not pay to exceed. The figure for all clays seemed to be pretty much the same. The purer the clay the larger the output. Coal dust suspended in oil behaved as a pseudo-colloid and was subject to the same laws as clay suspended in water, but that was a branch of the subject which had only just come into prominence. It would have to come

into very much greater prominence, because oil was getting in greater demand every day, and the supply was not growing at more than one-third of the rate of the demand, so that the question of mixing coal dust with oil was a problem of the very greatest importance.

It

Mr. HIGHFIELD said it was quite possible to dry peat economically; with a moderate consumption of electricity the water could be forced out of the peat, and when that was done the peat was in the form of little curled up bits of material like cocoanut shavings. The difficulty was to know what to do with the peat in that form. could be made into a briquette, but that involved a further consumption of energy, and unless it was made into a briquette it was difficult to carry, because it was bulky, and the cost of freight was high. If a peat was mined on a really large scale, tens of thousands of tons a month, the difficulty would be that, as the peat lies in moderately shallow deposit, it would be always running further away from the plant, as the plant could not be placed upon the yielding beds, so that the cost of bringing the peat to the plant was continually increasing and there were many other difficulties to be overcome apart from drying. He had to thank his colleagues for the enormous amount of work they had done on the paper, and Dr. Ormandy for having answered the questions raised in the discussion. He also wished to thank his assistants, who had been of great help in preparing the experiments.

The CHAIRMAN, in proposing a hearty vote of thanks to the authors, was sure the audience would agree that the experiments had been beautifully shown, and that the whole demonstration had been a model of its kind.

The motion was carried and the meeting then terminated.

GRINDING WHEELS: THEIR MANUFACTURE, USES IN INDUSTRY, AND FACTORS AFFECTING THEIR

SELECTION.*

By WALLACE T. MONTAGUE.

Pre

GRINDING is one of the most ancient of arts. historic man shaped his instruments of stone and later of metal by rubbing them on rocks which possessed abrasive qualities. It is not a matter of record when the idea of cutting out a circular block of stone, mounting it on a spindle, and revolving it by hand was first thought of.

Sandstones were originally used in the industries where grinding operations were performed, although the applicability of emery was generally recognised by the Greeks of the early ages, who found it on the island of Naxos. The extensive use of emery in competition with the sandstone was limited until around the year 1870, when a method was invented for binding the grains together with a suitable medium and forming the wheels into necessary shapes for use in grinding.

Improvements in the methods of manufacture of grinding wheels naturally included a betterment of the abrasive material, with the result that the artificial abrasive was developed to overcome the imperfections of the natural emery, and to make available an abrasive in sufficient quantity to meet the ever increasing needs of industry.

Abrasives. In general, there are two types of abrasive-aluminous and silicon carbide, the former consisting essentially of aluminum oxide, and the latter of a chemical union of the elements carbon and silicon.

Aluminous abrasives occur in nature as minerals in the form of emery and corundum. Aluminous abrasives are also manufactured by electric furnace methods and sold under the trade names "alundum," "aloxite," "borolon," &c.

Silicon carbide abrasives do not occur in nature but are manufactured in the electric furnace and sold under such trade names as "crystolon," "carborundum," "carbolon."

The Norton brand of aluminous abrasive, alundum, is made from the natural mineral, bauxite, containing as high a percentage of aluminum oxide as it is possible to obtain. The ore is carefully analysed and a mixture so made that the product of the furnace operation is fully controlled. The mixture is fused in an electric furnace of the arc type, and during fusion the material is purified and changed from soft bauxite into hard crystals of aluminum oxide.

The Norton brand of silicon carbide abrasive, crystolon, is manufactured by heating pure silica sand and coke together in a special resistance type of electric furnace. The material is not fused, but a chemical reaction results from the high temperature employed, with resulting crystals of abrasive.

Sizing the Abrasive.-The alundum and crystolon abrasives are received at the Norton grinding wheel plant in irregular pieces about six inches in diameter. This material is passed through a series of jaw crushers, rolls, washers, &c., and is *From Proceedings of the Engineers' Society of Western Pennsylvania, April, 1920.

finally sized by being passed through standard mesh screens. The standard grain sizes begin at 8 mesh and continue through 200. The flour which is left is designated as 200-F, and is further refined and classified by hydraulic means into such sizes as F, 2F, 3F, XF, &c. The number giving the size of the grain indicates approximately the number of holes to the linear inch in the screen through which the grain will just pass. For instance, a 30 grain will just pass through a screen having 30 small holes to the linear inch or 900 small holes to the square inch.

After passing over the sizing screen, the abrasive grain is stored in tanks, ready to be sent out as polishing material or to be used in the manufacture of grinding wheels.

Manufacturing Processes.-Grinding wheels are manufactured by four processes-vitrified, silicate, elastic and rubber.

By far the larger proportion of grinding wheels is manufactured by the vitrified process. In this process, the abrasive grain is mixed with the proper amounts of clay and water until the mixture has the consistency of a mud, which can be easily poured into moulds. After pouring into moulds, the wheels are taken to drying rooms and left until they are thoroughly dry. They are then shaved on special shaving machines to the approximate shapes and dimensions required, and placed in dry storage, ready to go into the kilns for vitrification. Vitrification in the kilns takes place at about the melting point of steel, and the length of time required for heating, the length of time held at high heat, and the cooling period are very important. Kilns are of the type used in the pottery industry, and are fired by a series of hardcoal fires uniformly spaced around the base of the kilns. In the larger types of kilns, it is approximately three weeks from the time the kiln is charged, until it is drawn. This time is absolutely necessary, and regardless of the emergency nature of any order, every wheel burned in the large kilns must remain there for the full time. After the wheels have been burned, they are sent to machines where they are shaped to exact size by means of hard metal cutters.

Silicate wheels, as the name indicates, are made by using a bonding material composed of silicate of soda. These wheels are made by tamping into iron moulds, and they are baked at a compara

tively low temperature. By this process, all

wheels 30 or more inches in diameter are manufactured, 60 inches in diameter being the maximum size that can be made.

Elastic wheels are made by using a bond having quite a degree of elasticity. The bond is of an organic nature and is composed mostly of shellac. These wheels are also tamped into iron moulds and are baked at a comparatively low tempera

ture.

Rubber wheels are made by mixing abrasive with rubber, and later, vulcanising the resultant product.

Silicate wheels are used largely in the cutlery industry in general to replace sandstone; and for all wheels over 30 inches in diameter, which cannot be manufactured commercially by the vitrified process. Elastic wheels are used where very thin wheels are required for cutting off stock; also for finish grinding of chilled iron rolls, and for other work where a fine finish is desired. Rubber wheels

are used on the same type of work as elastic wheels, except that they have a somewhat harder action and are, therefore, used only where grades harder than those made by the electric process are required.

Abrasive Action.-The abrasive action of an aluminous abrasive is dependent upon the amount of crystalline aluminous oxide present and also upon the temper or brittleness of the abrasive.

The best grade of emery comes from Turkey. It contains up to about 65 per cent of corundum, which is the form in which the cutting element occurs in emery. Emery mined in America has as low as 10 per cent corundum. The chief impurity of emery is magnetic iron oxide. Alundum abrasives contain more than 92 per cent of this cutting element, and a special alundum known as No. 38 contains more than 98 per cent aluminum oxide. Practically no magnetic iron oxide is present in these abrasives.

Artificial aluminous abrasives are more efficient than emery, because: (1) they contain a much higher percentage of cutting element; (2) being free from impurities, they are capable of variations in toughness to suit the work to be done; (3) they are made to a definite standard of composition and temper.

The grinding wheel to meet present day requirements must be a scientifically developed cutting tool. Its action when at work is similar to that of the steel milling-cutter. On the face of the wheel are millions of cutting teeth at work every minute, and although these teeth are not as long or as strong as the teeth of the steel cutter, and cannot cut as deep, they are capable of working at a much greater speed. Each little cutting tool, which in substance is a grain of abrasive material, cuts off a chip at each revolution. The chips resemble, in shape and character, the chips cut off by the milling-cutter.

Uses in Industry.--The uses of grinding wheels in industry to-day are many and varied. The great refinement attained in the case of the gasoline motor used for automobiles could not have been reached without the use of the grinding wheel and artificial abrasives. Likewise, the grinding wheel plays an important part in the manufacture of tractors, motor trucks, gas-engines used for farm purposes, &c.

The ball- and roller-bearing industry, which has grown up alongside the automobile industry, is likewise absolutely dependent upon artificial abrasives for the refinement and accuracy of its product. Being composed of hardened alloy steels, the only way that these could be brought within the required limits of accuracy and finish is by means of such aluminous abrasives as alundum. Likewise, the requirements of this industry are so great that existing supplies of natural abrasives, even though they were of proper standards of purity, would not begin to meet the demand.

The phonograph, the typewriter, the adding machine, the cash register, and other apparatus of similar nature could not be made as economically to-day, if it were not for the grinding wheel industry and artificial abrasives. The agricultural implement industry uses grinding wheels and abrasive grain in large quantities for the manufacture of harvesting and threshing machinery, ploughs, planters, &c. Even such activities as the

textile industry require grinding wheels for sharpening cards, snagging castings, and maintaining tools, cutters, and dies used extensively in keeping up its equipment.

The leather and shoe industry uses grinding wheels for the buffing of hides and for the sharpening of leather cutting and shaving knives.

The steel-mills use. alundum grinding wheels for grinding out seams of high-speed steel billets preparatory to rolling into bar stock. The steel, foundries use alundum wheels for snagging steel castings., Crystolon grinding wheels are used in foundries for snagging cast-iron castings, and for cleaning castings of brass, bronze, and aluminium.

The railroad industry has extensive use for wheels composed of artificial abrasives. Such parts as locomotive piston-rods and valves must be ground on cylindrical grinding machines; guide bars must be surface ground with alundum grinding wheels; steel car-wheel treads and flanges sometimes are ground with alundum wheels, and manganese-steel frogs and 'switches have to be surfaced and fitted with grinding wheels composed of aluminous abrasive.

The optical industry uses aluminous abrasive wheels for lens grinding, and aluminous abrasive grain for roughing out lens blanks prior to polishing.

The cut-glass industry employs the artificial grinding wheel to a very large extent in cutting the intricate designs that go to make up the beauty of this ware..

The marble industry employs silicon carbide abrasives in thin wheels for sawing marble into slabs, and in thick wheels for surfacing or moulding the marble into various shapes and designs.

The final polish on marble slabs used in interior building operations is obtained by means of abrasive blocks composed of very fine grit silicon, carbide or alundum abrasive, followed by putty powder.

Selection of Wheels.-The main points to con sider in the selection of grinding wheels are as follows:

1

Material.—Whenever a grinding job is presented to you, the first thing to think of is the nature of the material to be ground-whether it is hard or soft, &c. If it falls under the general head of a high tensile strength material-such as all steels and down as far as the hard grades of bronzes-then an alundum wheel of some kind should be used. If, on the other hand, the material falls in the, class of low tensile-strength materials such as cast-iron, chilled iron, brass, soft bronzes, aluminum, and copper-then you should use crystolon wheels.

Operation.-The next thing to consider is the nature of the operation to be performed by grind. ing; that is, whether cylindrical, surface, internal, sharpening, or off-hand grinding is demanded.

If the speeds deviate very much from these, and it is impossible to change them to suit our recommendations, then this must be taken into account in your recommendations. Speeds higher than those recommended call for slightly softer grades to offset the harder cutting action; and speeds lower than those recommended call for slightly harder grades than would be ordinarily supplied.

Work Speed. It is impossible to tell a customer the exact speed at which his work should be done on any given grinding job. It is largely a matter of experiment. The work speed should be suited to the wheel in use and the nature of the material to be ground. On the Norton cylindrical grinder, a speed of from 60 to 80 surface feet per minute is often used for roughing and from 30 to 40 surface feet per minute for finishing. On most types of precision grinding machines, it is customary to rough grind at a higher surface speed of work than on finish grinding.

Contact. Contact affects grade selection. Broad contact calls for softer grades and narrow contact for harder grades, as the case may be. This is especially true in snagging and off-hand grinding. Where wheels are used for grinding the burr left by welding, or for grinding sharp fins from castings, extremely hard grades, such as S, T and U, are called for. In cylindrical grinding, the contact varies with the diameter of the wheel and the work, increasing with larger work or with a larger wheel, and thus making a softer grade of wheel desirable.

Condition of Grinding Machine. This is something which you would really have to observe personally in order to understand how it would affect grinding wheel selection. If the spindle is loose and cannot be put in good condition, a harder grade of wheel must be used than would ordinarily be recommended. This is in order to overcome the tendency to pound the wheel face to pieces. Light, flimsy machines and machines improperly secured to the foundation also call for harder grades than would ordinarily be used. Machines are frequently placed in the middle of a wooden floor which vibrates badly and in this case barder wheels must be used than for a machine on a firm, solid foundation.

Personal Factor. This is extremely important in the operation of grinding wheels, frequently influencing the results obtained as much as 100 per cent. We mean by this that different men working on the same kind of machines and on the same work in the same shop will get one result, say 15 hours' life, whereas other men under exactly the same conditions might get 30 hours. This is based on records obtained and not on impressions, and explains why the same wheels will work differently in different shops.

(In the original, several woodcuts are given, illustrating the various apparatus, &c.).

NOTE ON BRANNERITE.*

By ROGER C. WELLS, Ph.D., U.S. Geological Survey. THE mineral brannerite described in a recent paper in the JOURNAL OF THE FRANKLIN INSTITUTE and CHEMICAL NEWS, CXX., was carefully tested for helium, as it was expected that a mineral consisting of nearly 50 per cent of the oxides of uranium, and also containing thorium, should show at least a trace of helium. None was found, however, by the method employed. It was found that some sulphur dioxide was produced by reaction of the mineral and sodium bisulphate, and after removing this with a solution of sodium hydroxide, the remaining gas did not show the characteristic yellow line of the helium spectrum. Shortly after the paper was published the advantages of purifying the evolved gases by means of charcoal and liquid air were brought to the attention of the writer by Dr. R. B. Moore, of the Bureau of Mines, and it seemed desirable to repeat the test, using this method. Some highly active charcoal was kindly furnished by Prof. A. B. Lamb, of the Fixed Nitrogen Research Laboratory, American University, for the purpose. clean-up of the gas by this method gave a decisive result indicating the presence of helium, which places the mineral in the list of uranium minerals in which helium has been identified. The test was conducted as follows:

The

About 5 grms. of brannerite was powdered and mixed with previously fused sodium bisulphate in a hard glass tube which was connected by a thick rubber tube to the Töpler pump. Between the hard glass tube and the pump were three stopcocks, and between the latter were sealed the tube containing the charcoal and a spectrum tube, respectively. The system was evacuated until a pressure of about 0.05mm. was permanently obtained while the charcoal was heated. The spectrum tube and pump were then cut off, leaving the stopcock between the charcoal and mineral open while the bisulphate was gently fused. The tube of charcoal was then allowed to stand in liquid air for about half an hour to effect a clean-up of the gas. Finally the gas was admitted to the spectrum tube and a little later the tube was sealed off.

The yellow helium line showed up strongly in the spectrum, and several other lines believed to belong to helium were noted. These observations were made with a spectroscope having an illuminated scale and the wave-lengths were read from a curve based on some familiar flame spectra. The method does not give more than three *Published by permission of the Director, U.S. Geological Survey

significant figures. The values found ascribed to helium were 6660, 5880 (yellow line), 5030, 4720, and 4470. Two lines, 6545 and 4870, may represent hydrogen, whereas 6070, 5620, and 5200 are believed to belong to carbon. Among other lines noted but not placed are 5470 and 7000. The spectrum may be examined more carefully later if it should appear desirable, but the first object in view was to establish the presence of helium. At the conclusion of the experiment it was found that approximately half of the mineral taken was decomposed by the short fusion with the bisulphate.

PROSPECTS OF CEREAL CROPS AND OF SUPPLY.

ACCORDING to the June Bulletin of Agricultural and Commercial Statistics, just published by the International Institute of Agriculture, the official estimate of the winter wheat crop of the United States of 1920 is for about 13.7 million tons and that of the spring crop for about 75 millions. Hence the aggregate yield of wheat in the United States will be 212 million tons, or 27 per cent below that of last year, though only 4'9 per cent less than the average of the five years 1914 to 1918. It should, however, be remembered that the actual quantity exported from the United States during the current season falls short of the available surplus, so that stocks at the end of this period will be greater than those held last year.

Canada reports an area under wheat 17 per cent above the average from 1914 to 1918 also an excellent crop prospect, and it is therefore permissible to estimate that the yield will be equal to the average of the period mentioned, and much larger than it was in 1919.

On the basis of these statements, it is reasonable to expect that the North American exportable surplus of wheat for the season 1920-21 will be larger than the exports during that of 1919-20.

Government control of wheat ceased in the United States on June 1.

Crop conditions for wheat are favourable in Germany, Bulgaria, France, England, Wales, Ireland, Luxemburg, Sweden, Egypt, and average in Scotland, Italy, Poland, Switzerland, and Czecho - Slovakia. In Hungary injury has occurred owing to the great heat in May.

The estimates of the recent wheat crops in British India have been increased from 9.9 million tons to 102 millions, and the new season is reported as developing normally.

The rye crops are favourably mentioned in France, Sweden and Switzerland, as in average condition in Germany, Italy, and Luxemburg, and as poor in Poland and Czecho-Slovakia. Vines and olives promise well in Italy. Rome, June, 1920.