March 26, 1915. THE COLLIERY GUARDIAN. 663 LETTERS TO THE EDITORS. The Editors are not responsible either for the statements made, or the opinions expressed by correspondents. All communications must be authenticated by the name and address of the sender, whether for publication or not. No notice can be taken of anonymous communications. As replies to questions are only given by way of published answers to correspondents, and not by letter, stamped addressed envelopes are not required to be sent. ELECTRIC SIGNALLING IN COLLIERIES. Sirs,—We 'have noted the leading article, “ Electric Signalling in Collieries,” in your issue of the 19th inst., from which we gather that the writer is unaware of Rule . 15 in the Special Rules for the Installation and Use of Electricity in Mines, which was published March 1912, and reads as follows :— (z.) All cables, apparatus, signalling wires, and signalling instruments shall be constructed, installed, protected, worked, and maintained so that ..in the normal working thereof there shall be no risk of open sparking. The manufacturers of signalling appaiatus have been alive to this rule, and we have designed, in conjunction with a colliery manager, a system known as the ’‘ Davis- Fryar ” mechano-electric signals for haulage planes in gassy mines, and the same is now extensively employed m Groat Britain. A contact-maker of special construc- tion is placed in a position where required, and actuated by mechanical pull wires, which run along one side ci the haulage road. These wires, which are carried by small supporting pulleys, are anchored at the end reniom from the contact-maker, and pass over a pulley near to it, and are kept taut by means of weights. Near to the last-mentioned pulley one end of a short length of flexible wire is secured, and the other end is attached to the contact-maker. The electric contact is contained in a strong iron case which is gasproof, the actual contact is immersed in oil, and a removable covers enables it to be readily examined. The contact-maker is double-acting, so that the pull wire may be run right and left, and thus double the length of road is served. It will be seen that a signal can be transmitted by pulling the-taut wire at any point. Now, with regard to sparking bells, the writer of the article says : ”... it is difficult to conceive the possi- bility that so simple and useful a contrivance as an electric bell cannot be placed beyond suspicion even in the most fiery pit.” It is obvious that he is not familiar with the ” Davis-MacDonald ” solenoid bell, the construction of which is devoid of all contacts, an iron plunger being encompassed by a coil of wire, suit- ably wound. The ends of this wire are connected to the switch or contact-maker. When the current is applied this iron plunger is sucked up, and in so doing strikes a gong, and there is no possibility of sparking. The mechano-electric signals and also the bells just described are in use throughout the country, and we shall be glad to make arrangements for any of your readers to see examples at these works, or in actual operation at the nearest colliery. John Davis and Son (Derby) Limited. (W. H. Davis, managing director). All Saints Works, Derby, March 22, 1915. MINING DISCUSSIONS. Sirs,—Your correspondent, Mr. Halbaum, complains of the unimportance of first discussions at professional meetings. In this and other remarks he is not doing himself justice, and he omits certain features of the matter,. We have to keep in mind that professional societies exist chiefly on the basis of their claim to get and spread knowledge of practical means of safety (which nowadays also includes profit as a result of safety) and profit in mining operations. The institute has to keep on the hunt for men who know the safety facts or possess tools whose use tends to make mining safer and cheaper. Direct, tangible, practical, actual safety facts and tools are what the mining officials and his society requires. By accepting membership, we accept the duty of reporting and recommending practical facts and tools found useful in mining operations. The societies’ atti- tude is ” give us the facts—facts of correct principles, things and results of usage as life and profit savers,” and as most members are active mine officials (and therefore men constantly busy doing some act or using something for profit and safety of their men and masters), it is up to them to .recommend any fact or tool having life- and profit-saving value. On the other hand, the members’ attitude to the society is ” give us- informa- tion of fact and tools useful for life- and profit-saving in mining operations.” The idea of both society and members is active usage of practical facts and tools for the principal basis and object of preventing injury to the miner, and preventing financial loss to the master. A paper is a statement of facts. If it is not so, it has no business at a meeting, but as members are of all kinds of people, reasonable latitude is allowed, and papers often contain mere notions, ideas, and views which are partly mere literary verbiage, sometimes of a thought- breeding character, and often of an inspiring nature. The members are fairly generous to the notionalist, and democratic among themselves. The paper is read, and unless the reader is also a student of pitman nature, he is apt to be frozen by the chilliness of most members (those who are apt .to think deep and long), or drowned by the cold water brigade (those having preconceived opposition ’ to the main features of the paper), or roughly handled by the puff- devil pull-baker class (who will persist discussing wrong points). The reader must exercise patience and charity. So long as his facts and tools are right, he will get through the Slough of Despond, for besides the vitality and solidity of his facts, there are present always a few men who take serious notice of his views, and who look at them from the proper point of view. Let the reader talk to these—it is only the user of his facts that matters —and the sympathetic man can only appreciate the facts. If the reader loses his sangfroid, if he is tempted to sit down and nurse his bruises of misrepresentation, let him remember that time heals all sores. The paper reader must also take a more serious view of his task before he ventures. If the facts and tools are vital, and the possessor lets go his hold, it is a bad day for mining, for the cost and tragedy lists will show results. So I must ask Mr. Halbaum to take long, broad, and cheerful views of mining men and discussions. He is one of the’' few mining men who write with vigour mixed with brains and courage. Whether right or wrong in his ideas, his notes are dynamic—and it’s the live man that matters. He must remember that many of his readers are hindered in conception by the text-book errors 50 years out of date. He might also get back to practical mining fact and philosophy (to which we are accus- tomed), and let go the merely logical (consistency of inference from premisses whether right or wrong doesn’t matter) papers of recent date. I don’t agree with his “winding friction” paper, as it is merely abstract, instead of pit-fact. Still, he can let go his part as a mere logician, and keep to his real part of mining investigator. Some day it may be as honour- able and profitable to be a mining investigator and philosopher as it now is to supply compensation and fittings required after disasters preventable by the facts and tools placed by investigators before our societies. So that impressions from first discussions are not likely to be full enough for sound judgment, but so long as the reader keeps pelting the facts at mining men, he may rely on some of the facts sticking. M. C. March 22, 1915. EFFECT OF SALT IN COKE OVENS. Sirs,—In your recent issue, under the heading of ” Current Science and Technology,” appears an extract from an address by Mr. F. W. Broadhead at the autumn meeting of the Society of British Gas Engineers, on the effect of salt in coke ovens, the destruction of the brick walls being ascribed to the action of the sodium. Owing to the extended use of coals high in oxygen for coking purposes, any information on this subject should be of interest at the present time. My experience shows that the destruction of the brick lining is due to the action of hydrochloric acid and chlorine gases, and this was confirmed by the following experiments :— An analysis of the coal showed that it contained :— Sulphur 1’60 per cent., of which 0 82 per cent, was with the iron, and 0’78 per cent, with the lime forming part of the ash content. Chlorides 0'89 per cent. Manganese 0’50 per cent. Analysis of new firebrick— Per cent. Silica ................................ 92’4 Iron, &c.................................. 7’6 Analysis of old firebrick — Silica ............................... 94’6 Iron, &c.................................. 5’4 Acting on the assumption that at the high tempera- ture this sulphur is liberated, which, when oxidised, would decompose the chlorides, setting free hydro- chloric acid and chlorine gases, just sufficient limestone to fix the sulphur with the lime was added to the coal before carbonising to form an infusible sulphide. i i Coal with Coal only. limestone added. Per cent. Per cent. Sulphur in coke..... 1’63 1’56 As FeS.............. 0’81 0’00 AsCaS .............. 0’82 1’56 The gases were tested by absorption of chlorine, the solution afterwards evaporated to dryness, with the following result :— With Coal only, limestone Increase, added. Percent. Percent. Percent. At 12 hours* coking in gases 0’58 ... 0’72 ... 24’4 At 18 hours* coking ........ 0’42 ... 0’56 ... 33’3 At 24 hours* coking ........ 0’17 ... 0’24 ... 41’1 These tests show that the chlorine with the gases is now in greater quantity, and not left behind in the oven to attack the iron in the firebrick lining. The addition of limestone ,considerably decreased the time of carbonisation. Tests with Fik ebrick. (1) Firebrick 40 parts, Salt 10 parts, In ph ces and crushed, fused for five hours at a temperature of 1,200 degs. Cent.— result, no effect whatever. • (2) Firebrick 40 parts, Salt 10 parts, Iron sulphide 10 parts, In pieces and crushed, fused for five hours at a temperature of 1,200 degs. Cent — result, firebrick corroded and pitted, the crushed portion partly fused as in the ovens. The oven was run for nine months on the limestone treatment, the firebrick lining during this period not being attacked or destroyed. During the above tests it was noticed that in the oven where limestone was added to the charge, a larger volume of gases were evolved, and the quality of the coke ■ improved. As practically all coals contain chlorides, it was decided to make further tests, on coals high in oxygen, to ascertain the action of limestone during carbonisation. A special oven, on the lines of the modern coke oven, was built, and numerous tests made with charges of coal, varying from 21 to 8 cwt. The oxygen content of the coal used varied from 6^ to 13 per cent. Charges with and without limestone were carbonised, the weight and grade of coal being the same in both cases. In every case it was found that the catalytic agency of the limestone reduced the temperature considerably, at which decomposition of the resinous and other matters commenced, and facilitated the combination of the occluded oxygen with hydrogen, contained in the coal, to -form water vapour. The primary products of car- bonisation consisted of water vapour and saturated hydro- carbons, principally naphthenes, no oxides of carbon being formed. The use of limestone added to coal, with a high oxygen content, opens up possibilities of an increased production of the supply of oil suitable for explosive purposes. The cresol at present found with the tar oils should, in this case, be recovered as toluol. 31, Station-street, A. Rollason. Nottingham, March 20, 1915. BOOK NOTICES. Business Prospects Year Book, 1915. Ed. Joseph Davies and C. P. Hailey. 228 pp. 5 in. x 7| in. Cardiff : Business Statistics Company. Price, 10s. net. The task which has lain before the editors of this little annual on the present occasion has been truly formidable. Under ruling conditions the gift of prophecy, practically considered, is a drug on the market, and Messrs. Davies and Hailey have wisely confined themselves to safe lines of reasoning. Where a work of this unusual description can help is in giving an accurate survey of the conditions, as regards supply, existing on the outbreak of war, concerning which more or less exact information is available. With respect to the future, the deductions made are by no means haphazard, and we should not be surprised if in many cases they are realised. A Text-Book of Practical Assaying. By James Park. Revised and enlarged from third New Zealand edition, with illustrations, pp. 342. 7^ in. x 5 in. London : Charles Griffin and Company Limited; 1914. Price, 7s. 6d. net. This is intended for the use of mining schools, miners, and metallurgists, and is the authorised text-book for New Zealand Government Schools of Mines. The matter covers the ordinary two years’’course in assaying, and the arrangement is such as a teacher might adopt in a series of lectures leading from simple to complex analyses. Covering as it does a very wide field, some portions of the book are necessarily treated in a some- what concise way. Rather more than half the number of pages in the book treat of common metallic ores, and the greater portion of this space is devoted to the precious metals of more common occurrence, with no notice of the rarer metallic elements. On the whole, this is com- mendable. A school lecture course, after all, is only a means of teaching principles in a limited time, and the main object is to make students careful and accurate in their work, rather than ton teach them a wide range of special analytical methods. For this purpose we think that Prof. Park has made a wise selection of subjects for laboratory assays. The disadvantage of .embracing such a wide field as silicate analysis, water analysis, fuel analysis, in addition to ore .assays, is the danger of leading students to believe that they know more than they do. No two years’ course would qualify a student to make a really competent analysis of such widely different substances. But he should possess a sound foundation upon which to specialise, and this he can doubtless achieve by conscientiously following this text- book. There is a rather perplexing reference on p. 223, which is evidently a misprint, the student being referred for information on the alkalies to chapter xviii., on the estimation of tungsten, titanium, etc., whereas the Lawrence-Smith method, which he really wants, appears in chapter xx. The chapter on the analysis of coals is somewhat briefly treated, but contains quite as much as the ordinary two years’ student could be expected to require. Useful cautions are. given where necessary, and the student is taught that even so apparently simple a matter as the determination of moisture in coal is fraught with difficulty and possibilities of error. It might here have been useful to add that the difficulties are far greater in the case of certain classes of coal. There is also a useful chapter on the examination of oil shale for petroleum, and others on a variety of materials likely to come before the mining engineer, who, if he will ’ only • still regard himself, after working through this course, as a mining engineer, and not as a chemist, will have done much to improve his professional attain- ments. Reports of Cases Decided by the Railway and Canal Commissioners. Vol. XV. Ralph Neville, LL.M., and W. A. Robertson, B.A. xvii. + 361 pp. 6J in. X 10 in. London : Sweet and Maxwell. Price, 37s. 6d. net. Many attempts have been made to improve the pro- cedure'of the Railway and Canal Commission Court, or to dispense with the tribunal altogether; little success, however, has attended such movements up to the present, and therefore, the proceedings of the Commis- sion continue to be of first-rate interest to traders. . For this reason, and, further, because railway law is so largely a matter of precedent, this carefully edited series of volumes is a boon to those who are not always on the best of terms with the “common carrier.”