(59) 117460

(Sr: 2HCl aq.)

= 117050

(60) 2(24350) + 67950

= 1.836

=

2.25

Evidence from Mineralogy that Sr = CaTi (64) Titanite, an oxide of Ca, Ti, Si, occurs in syenite at Strontian in Argyleshire. This is the locality from which strontianite (SrCO,) is obtained.

The volume 30.68 is exactly correct for three independent reasons:

(A) It can be split up (No. 3) into two

parts, which have been shown to be volumes respectively of Ca and Ti both here and in the paper on barium (Chemical News, 1925, CXXX., 307). (B) It is found (No. 37) to be the original volume of the element by means of the H.F. 70752, which occurs 4 times in Table IV.

(C) It is also found (No. 38) to be the orig. vol. by means of the H.F. 56725, which occurs 6 times in Table IV.

et. seq.

The volume 23.98 is exactly correct for 9 independent reasons:

(A1) It can be split up (No. 4) into two parts which have been shown to be volumes of Ca and Ti;

(A2-A7) It occurs 6 times in Table II.

Each experimental determination of S.G. is absolutely independent of all others.

(A8) It requires the same original volume as the other (No. 38) by the law of

H.F.

(A9) It satisfies the law of magnetic rotation exactly (Table V.)

The volume 19.56 is also exactly correct for 9 independent reasons.

(B1) It can be split up (No. 5) into two parts which have been shown to be volumes of Ca and Ti.

64 experimental facts obtained by scientists who are or were experts in their several domains, are here given, together with about the same number of deductions, which are evidently correct. Each one of these deductions leads up to the definite conclusion that an atom of Sr has been formed by the union of one atom of Ca with one of Ti.

The only experimental datum required in order to make the matter complete is that an atom of Sr may have a relative volume of 30.68 in the free state, i.e., that it may have a specific gravity of 2.868 (= 88 ÷ 30.68), especially when it is deposited electrolytically from SrCl,.

In order to be certain of this, an experimentalist would have to be quite sure that the element does not absorb heat from surrounding objects after deposition so as to reach the volume 35.1 given in No. 7.

In addition to demonstrating the structure of Sr by means of four sets of experimental data, viz., At. wt., S.G., H.F. and M.R., this paper accomplishes the following objects:

(C1) It continues the reduction of the experimental data of S.G. to exact instruments of research.

(C2) It strengthens the Law of Relative Volume.

(C3) It strengthens the Law of Heat of Formation.

(C4) It demonstrates the causes of Thom

sen's observed experimental effects, not necessarily of his calculated effects.

(C5) It strengthens the Law of Magnetic Rotation.

(C6) It continues the demonstration of the Co-relationship of Physico-Chemical Constants.

VALUE OF INDUSTRIAL RESEARCH. U.S.A. BUREAU OF STANDARDS VISITING COMMITTEE PUTS EMPHASIS ON BASIC RESEARCH.

Cites examples of its value in the past; believes more to come in future. Industrial research also held essential to prosperity.

The value of basic research, aimed at the acquisition of knowledge without immediate utilitarian objectives, was emphasised in

the report of the Visiting Committee of the Bureau of Standards (Dept. of Commerce, Washington, D.C., U.S.A.). The committee expressed the belief that such work should be undertaken by the Bureau to a greater extent than has been done in recent years.

The history of civilisation is filled with illustrations of the utilisation for the good of humanity of the results of scientific work, undertaken without reference to its direct value, and often remaining unused long after its first announcement," the report states. Illustrations given are the electrithe cal industry, radio, vacuum tube, X-rays, and radium. In each case the fundamental discoveries that made inven- ́ tion possible were made without thought of possible utility. Similarly, the present day study of atomic physics is cited as a line of research that is likely in the future to yield results of vast proportions, and as yet undreamed of.

The report also calls attention to the value of industrial research-a value more generally realised. Numerous examples of savings effected by such research at the Bureau of Standards are given. Studies of certain problems pertaining to the automobile industry are cited, whose combined result is a saving of $155,000,000 per year to the American public.

Both types of research, the committee believes, are essential to the welfare and industrial prosperity of the nation. The economies resulting from them are often very considerable, and are necessary if America is to maintain its present high wage rates and high standards of living in the era of intense industrial competition upon which the world now appears to be entering.

The desirability of having research conducted by a national institution is emphasised Its value depends on the extent to which the results are utilised rather than upon the cost of the work, and a national laboratory such as the Bureau of Standards can afford to give its results freely to all who can profit by them, whereas a private laboratory cannot always be expected to do

ᏚᏅ.

The Visiting Committee is composed of Dr. Wilder, Dr. Barecroft, Corwell University. Ithaca, N.Y., Mr. Gano Dunn, N.Y., U.S.A., Dr. William F. Durand, Brooklyn, N.Y., Dr. Samuel W. Stratton, Massachusetts Institute of Technology, and Mr. Ambrose Swasey, Cleveland, Ohio. The

in

Board of Visitors have issued a very interesting report. Incidentally, it is noted that the Bureau of Standards is being carried on in accord with the organic aid of Congress, which gives it the custody of National Standards of Science and Industry, invests it with the function of comparing such standards with like standards used scientific research, industry, commerce, and education, with the duplication or multiplication of such secondary standards with the testing and calibration of measuring apparatus; with the solution of problems which arise in connection with standards and with the determination of physical constants and properties of materials. The report deals with the wide range of the activities of the Bureau, and is convincing evidence of the extremely useful work in which it is engaged.

By DAVID BROWNLIE. B.Sc. (Hons.) Lond., F.C.S., M.I.Chem.E., A.M.I.Min. E., etc. Read before the Manchester Geological and Mining Society, on May 12, 1925.

(Continued from Page 390.)

The subject of pulverised fuel firing is such an enormous one that it is always extremely difficult to give a broad survey of the facts within any reasonable amount of space. However, in conjunction with the new plants already described, a discussion of the following items will fairly well cover the ground as regards the very latest developments.

DRYING.

A very considerable revolution has taken place during the last year or two in connection with the drying of the coal before pulverising. In the old days, down to 1% moisture was regarded as essential, but this is now known to be entirely unneccessary. In general, all that is required is the removal of what may be termed the added or mechanical, moisture, as distinct from the natural moisture in the coal itself, and, of course, that obtained by chemical decomposition of the coal substance. Roughly speaking, average figures to-day at 9-12% moisture in the coal as received, which is dried down to, say, 3-5%, and the only dif

ference in a modern type of mill as compared as coal 1% moisture is a very slight lowering of the output. It was the added, or mechanical moisture only that caused the trouble in the way of great reduction in capacity and increase of power, which resulted in the opinion that all moisture ought to be got rid of.

Thus, for example, as the result of most detailed investigations carried on at the smaller Brunot Island power station of the Duquesne Light Company, at Pittsburg, before the installation of this method of firing at the much larger Colfax station, local coal containing up to 5-6% moisture was pulverised and used without difficulty, the only trouble being a slight reduction in the capacity of the pulverisers.

In this case a good quality run of mine coal from an adjoining pit was used, having the average analysis of fixed carbon (dry basis) 56.0%, volatile matter (dry basis) 33.0%, and ash (dry basis) 11.0% with 3.5% moisture, 1.5% sulphur, and a heating value of 13,500 B.Th. U. (dry basis). Very often the moisture figure went up to 5-6%, but, as already indicated, no dryers are used.

or

As regards the plant for carrying out the drying operation, the long horizontal slightly inclined separately fired cylindrical dryer revolving at a slow speed of about 3-4 revolution per minute, is now beginning to be regarded as obsolete, at any rate so far as steam generation is concerned. The modern principle is the small vertical selfcontained continuous gravity dryer situated between the overhead crushed coal bunker and the pulveriser mill below, forming a neat and efficient combination. The rotary apparatus has the disadvantages of being enormous in size, especially as regards length, and occupies a very large amount of valuable space, approximately 40 cubic feet per ton of coal dried, whilst the capital cost is heavy and the labour and attendance considerable. Also the total nett power necessary for operation is somewhat excessive, approximately equivalent to 1% of the 20al burnt, the fan for drawing the heated air through having to be about 1.000 cubie feet of air per minute per ton of coal dried. Further, the continual churning up and agitating of the coal creates a very dusty atmosphere, increasing the risk of fires and nearly all caused, directly or indirectly, by explosion, which in the early days were the dryers.

Also, the rotary dryer is not particularly efficient from the point of view of heat

transmission, as with all cylindrical apparatus of this character, whether for drying, carbonising coal, and other material, or in various chemical operations, such as cement manufacture. The heated air naturally always tends to pass right through the cylinder above the coal or other material, whilst methods to try and increase the contact are extremely complicated, and result in much increased power consumption.

The modern vertical gravity coal dryer on the "Wood" principle was operated experimentally at the Oneida St. Station of the Milwaukee Electric Light and Power Company for the two years 1921-1922, and the first large installation was that at the Cahokia station, St. Louis, as already indicated, whilst to-day the principle is in operation or being installed in a large number of the most up-to-date boiler plants in the world, such as the Cleveland, Trenton Channel, and many other stations in the United States, Vitry and Gennevilliers in Paris, and Willesden, St. Pancras, Birmingham, and Derby in Great Britain. As is well-known, the design consists in the use of a comparatively small vertical cylinder placed between the crushed coal bunker and the pulveriser containing inside two louvred pipes or narrow diameter cylinders, the coal passing downwards by gravity as taken away by the pulverisers underneath.

Part of the hot exit chimney gases, roughly about 10% of the total equal to 3 lbs. of gas and air, 1.0 lb. coal, are taken by means of a fan and suitable trunking, the arrangement being illustrated clearly in Fig. (1), generally mixed with air to give a temperature of about 215° F., and circulated continuously through the dryer back to the chimney again. The total power required is only about 3 K.W. per ton of coal, say, equal to 0.15% of the steam production of the plant. The design has been proved to be extremely effective, being simple and efficient, occupying practically no space of importance, whilst the labour is negligible. The heating surface is the extremely small figure of about 25-35 square feet per ton of coal per hour. As regards the temperature of the air and flue gas mixture, it now seems to be regarded as the best practice to have a figure of 250°-400° F. entering the bottom of the dryer, with 150° F., leaving at the top. the cold air supply damper being adjusted to give a final exhaust gas temperature of 25°-50° F. higher than the dew point. It is apparently not necessary in many cases to have the exhaust temperature as high as

212° F., as hitherto considered essential, and 150° F. is quite sufficient provided the gases are not saturated and there is no danger of re-deposition of the moisture at any stage of the drying.

are

The very latest development of the continuous vertical gravity dryer is the use of air combined with exhaust steam heaters instead of air mixed with hot flue gas. These steam heaters are on the lines of the ordinary gilled steam radiator and placed in the vertical drying cylinder, whilst there is passed through them inside low pressure steam, either the exhaust of any convenient steam driven auxiliary plant or "bled "specially from the turbine. The hot condensed water is returned to the boiler plant so that the dryer really functions as a condenser in which the heat is usefully employed in drying coal instead of being lost in the cooling water. In this new type of dryer, about 30 square feet of heating surface per ton of coal per hour is required for every 1% moisture, whilst the amount of air passing through is about 1/3 that of the air and waste heat dryer, that is 1 lb. of air per 1 lb. of coal. This is because the air from the boiler house is moderately dry and does not contain already a large amount of moisture, as in the case of hot flue gases.

Other minor advantages of this design are that the fire risk is nil, although almost negligible with the waste heat dryer, whilst the amount of coal lost as dust is approximately 0.01% with the air and exhaust steam dryer instead of 0.1-0.25% with waste heat.

PULVERISING.

The main developments in pulverising during the last year are in the first place that it is not now regarded as necessary to dry the coal to excess, as already discussed in detail. The standard mill is practically the vertical, centrifugal, completely-enclosed roller type, with 4-6 rolls, having a continuous gravity separation of the pulverised fuel by means of a current of air. The power used varies between 9.5-18.0 K.W. per ton, depending on the character of the coal, which is, of course, very important, and the general operation, including the items of wear and tear, maintenance and cost of upkeep, is very satisfactory.

Another important point is that excessively fine grinding, such as 65% through a 200-mesh is now shown to be unneccesary, provided that uniform particles are obtained, say 95% through 100 mesh. ideal would be 100% through 100-mesh, and

The

it is no use having a large part of the fuel pulverised to excess if a number of large particles are contained in it. Roughly speaking, however, with modern mills and average fuel, 90% through a 100-mesh is equal to all through 50-mesh and 70% through 200-mesh.

COMBUSTION CHAMBER CONSTRUCTION.

As is well-known, the main points of combustion chamber constructed for pulverised fuel firing as applied to water-tube boilers, as shown in Fig. (1), are hollow air-cooled walls, very large volume, and the water screen. It is the furnace end of pulverised fuel that has always presented the most difficulties because of the intense heat developed, and the serious erosive and other deleterious action of the molten ash. To-day the extensive application of this method of firing is prevented in the iron and steel and many other industries mainly because of the slag and the wear and tear on the brickwork. In steam generation, however, with water-tube boilers, there is no question the problems have been solved mainly by the combined effect of air-cooling the brickwork and installing a series of water-cooled 4 inch steel tubes in the bottom of the furnace, that is, the water screen. As a consequence, the ash is kept very cool and does not melt. Combined with this is the use of a very large combustion chamber, and burners placed at such an angle that no part of the flame can impinge on the brickwork, so that the combustion must be completed before reaching the boiler tubes. All kinds of refinements are, however, being continually introduced.

feeders supplying the burners. This raises the cold air to about 75° F., cooling the arches without wasting any heat.

One of the most remarkable of later inventions is the " Murray water tube or fin" wall, the invention of Thomas E. Murray, and first applied about 12 months ago at the Hell Gate Power Station, New York, in conjunction with multiple retort mechanical stokers. Essentially the principle consists in constructing the two side walls of the combustion chamber and the back wall as well, if necessary, of 4 inch steel tubes placed at 7 inch centres. To the side of each tube is welded a projecting steel plate or fin, one of which is 24 inches, and the other 1 inches from the tube surface. These plates or fins overlap, so that the wall is built up of 4 inch tube and 3 inch steel plate. The feed-water circulates through the tubes, entering by means of a common header at the bottom and being discharged through a common header at the top into the boiler. The result is an enormous increase in the nett heating surface of the boiler next to the combustion space for the absorption of radiant heat, and remarkable results have been obtained at Hell Gate, up to 92.7% boiler plant efficiency with mechanical stoking by the use of this appliance.

The Murray "wall is now being adopted for pulverised fuel as an addition to the water screen, so that very soon we shall have combustion chambers almost entirely constructed of water-cooled tubes.

A further interesting invention, at present mainly used in conjunction with the travelling grate stoker, is the suspended fire-brick arch on the "Detrick- Usco" and "Liptak" principles, which is being applied to pulverised fuel. The principle consists essentially in building the arch or roof of the combustion chamber of a series of interchangeable standard firebrick blocks having a tee slot in the top, suspended from flat heavy steel girders having cast iron supporting or arch bars that fit into the slots. In this way a composite roof can be constructed of any span or shape, merely depending upon the strength of the girders, and the wear and tear is very greatly reduced as there is no strain on the individual blocks due to expansion, contraction, or compression of a mass of brickwork.

(To be Continued.)