March 20, 1914. THE COLLIERY GUARDIAN. 637 LETTERS TO THE EDITORS. The Editors are not responsible either for the statements made, or the opinions expressed by correspondents. Ill communications must be authenticated by the name and address of the sender, whether for publication or not. No notice can be taken of anonymous communi- cations. A.s 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. THE STAFF EKCMEEM’ ASSOCIATE. Sir,—The Staff Engineers’ Association has recently published a small pamphlet, which embodies the following appeal to civil, mechanical and electrical engineers :— “ This little booklet, ‘ The S.E.A.,’ defines the aims of the Staff Engineers’ Association. It is now for staff engineers to decide whether these aims are to be realised. Your own individual attitude at the outset will be of vital importance. You will agree that the initiation of a movement of this nature is a laborious and wearisome task. Through the energy, per- severance and zeal of a few of your fellow engineers, however, the spade-work has been accomplished. The association now exists. It is here to help you—if you will appreciate it, and realise its potential value to you. “We appeal for your support. It is now, at this initiatory stage, that your help is most needed. Remember that, although you, personally, may not require the facilities offered by the association, you can, through the medium of the new institution, assist your less fortunate brethren. Remember also that upon the response to this appeal the future of the association will depend. If you are already a member, we respectfully claim the assistance you can give to the movement, by propagating its objects and by effecting the enrolment of your friends.” The booklet referred to gives the objects and rules of the association, which is being established to further the economic interests of its members, and to promote in public and commercial circles a higher sense of the rank of the engineering profession. The annual sub- scription is 20s. and 15s. respectively for members above and below 30 years of age. Copies of the booklet can be obtained on application to L. H. Fletcher, 31, Queen Victoria-street, Hon. secretary, London, E.C. Staff Engineers’ Association. WORKING HIKERS MO THE MMMER’S CERTIFICATE. Sir,—There is so much that calls for reply in Mr. Machin’s letter in your last issue, and there are so many exaggerated views, that one scarcely knows whether a letter in reply will be too lengthy for your columns. This question of candidates’ plans has been previously discussed in other mining journals, and the same idea still seems to prevail, namely, that there are managers— no one has yet estimated their number—who are of such a dog-in-the-manger spirit that they will deliberately put a stumbling-block in the way of a working man intelligent enough to have worked himself up to the status of a first-class candidate. If there are any such men, surely, sir, they are very few and very far between. Naturally a manager or head surveyor would think twice before lending a dial to a man who had never handled a more delicate instrument than a pick; but in how many cases does a man require to present himself for a first-class certificate who has never risen to some kind of official position, where he would probably have assisted the surveyor himself on more than one occasion ? Your correspondent says “ he has to borrow £50 worth of delicate instruments.” Since a trigonometrical levelling will be accepted, no telescope is needed, and a good dial, such as Casartelli’s, would cost about £20 when new, including tripod. A chain would not cost more than £1. As to assistance: There, again, if a man was known to be intelligent and anxious to get on, he could get an apprentice or, in some cases, the under-manager and one or two of his mates to help him. To the lay mind a working man appears to be debarred by legislation from improving himself, but when looked at from the practical point of view there is a different aspect. As to damage to instruments, could not the man under- take to pay for them himself ? If he broke the glass it would not cost a fortune, and a man up to first-class standard should have learnt by then enough to realise that a dial must be handled with reasonable care. After all. a strong brass dial is not such a very delicate surveying instrument, comparatively speaking. It certainly may seem hard on a second-class candidate being refused admission, but it is generally because he has not done any actual coal-getting. I know a case of a man being told by the Board of Examiners to go coal-getting for 12 months and then to apply again. I fail to follow the trend of Mr. Machin’s argument as to the age a man might reach before being able to sit for a first-class certificate. If he cannot sit till he is 30 years of age or over, it is probably because he has not been fortunate enough to be able to serve his time as an apprentice. One imagines that such a state of affairs comes under the head of “ Accident of birth,” for which no one has yet found a remedy; so why should the Board for Mining Examinations in this country be blamed for it ? I agree with Mr. Machin that some other method of testing a candidate’s practical surveying knowledge could be adopted. Personally, I would welcome a practical examination down a pit near the examination centre, just as the examiners for honours in the City and Guilds of London Institute hold a practical exami- nation in theodolite work in a local park at the town where the examination isffield. Surely it is rather a broad statement to say that the Government Act is “ killing mining education amongst workmen.” Would Mr. Machin give this as a reason for the statement by Mr. N. T. Williams (lecturer in mining at Manchester University), as reported in your issue of the 6th inst., that only 1,000 out of 100,000 men engaged in mining in Lancashire were attending evening classes ? Is not Mr. Williams’ solution correct, “ that it is due to the growing craze for evening amusements amongst the rising generation of miners,” resulting in loss of sleep and rest and consequent lack of mental alertness ? Everyone knows that mining education is dirt cheap, if men will only take advantage of it. Surely, under our municipal system of education, our Governments do all they can to facilitate and encourage. Trusting I have not trespassed too much on your space. March 16,1914. Wiganer. A KEW TYPE LONGWALL COAL-CUTTER. Sir,—Under the above heading, in your issue of the 6th inst., there appeared an article describing an American longwall chain machine, and palpably emanating from some interested source. At all events, I trust that, in common fairness to British manufac- turers, the views therein expressed are not those of the Colliery Guardian. The insinuation that in the manufacture of longwall coal-cutting machines American firms have had more scope than their British contemporaries is entirely misleading. The reverse is the actual fact, since long- wall machines are comparatively little used in the States, and the American manufacturer will find he has a good deal to learn in designing machines suited to the conditions met with in this country. A further mis-statement is that “in its inception the longwall coal-cutter was the disc.” As a matter of fact, the chain type longwall machine anticipated the disc, and the latter has outstripped it on its own merits, and is bound to do so in this country, though there are doubtless plenty of seams where the chain and bar types are more suitable, and for these conditions there are already excellently designed British-made machines. To say that “ a satisfactory chain machine is certainly preferable to a revolving disc ” is equivalent to stating that a satisfactory cow is preferable to a horse, and for given services such a statement is incontrovertible. Each type of coal-cutter has its own particular sphere of usefulness. I have no desire to criticise this particular American coal-cutter designed for British conditions; but there are certain features which require amending before it would be acceptable to the user who has any practical experience of such machinery. I repeat that I trust the article referred to does not represent the views of the Colliery Guardian, and that the concluding statement, “ In our opinion, it is a distinct advance in the design of coal-cutting machinery,” is that of the selling agent, and that you, Sir, dissociate yourself from such an expression of opinion, which could hardly be regarded as satisfactory to British manufacturers. Sandal, Wakefield, G. A. Bousfield. March 12, 1914. [Without entering into a discussion of all the points raised by Mr. Bousfield, we may make the following observations:—(1.) The article in question did not emanate from an interested source, but was written, after investigation, by an experienced and entirely disinterested engineer, whose name, if disclosed, would be familiar to our readers. (2.) The writer of the article disclaims any intention—and we certainly read no such intention ourselves — of insinuating that American firms had had a greater scope for the development of longwall coal-cutting machines; on the other hand, the scope for the development of coal-cutting machinery in general is manifestly greater in the United States, owing to the much larger proportion of mineral got by machinery, as compared with this country, although the longwall type of machine has been more greatly developed in Great Britain. The statement that “ in its inception the longwall coal-cutter was the disc ” was not intended to be meticulously accurate as a matter of history, but we think it will not be challenged that most of the early manufacturers began with the disc ; it is the machine with which experience has been chiefly gained, and is, perhaps, best known to users in this country. We should certainly never have allowed the Colliery Guardian to be the medium of a premeditated assault upon British makers of coal-cutting machinery, but we cannot place this construction upon the article. Mr. Bousfield and others have brought the British machine to a high pitch of excellence, and we hope that our most competent correspondent will favour us with some genuine criticism of this new Jeffrey machine.—Eds. C.G.l_________________________________ FLAW v. ELECTRIC SAFETY LAKIFS. Sir,—Mr. Joel in his letter published in your journal of March 13 gives some figures relating to candle-powers of lamps ; but in view of the figures given by the writer in recent issues of your journal, and supported by Dr. Llewellyn and others, it seems to the writer that as no new conditions or improvements have since been introduced, either by Mr. Joel or other parties, which could produce better results than the lamps and bulbs upon which our tests were carried out, it is beside the point for Mr. Joel to be again writing about what happened at Eskmeals to five of his lamps, when he must know that the lamps on the market to-day are not giving 1-candle power for nine consecutive hours. If he has been down a coalmine he ought also to know that a lamp with a bulls-eye for a miner is unsuitable, and that the Government have decided that the miners’ lamp must have an all-round light of 1-candle power, and Mr. Joel should know very well that the high candle-powers “ in the beam ” which he refers to are of little or no use to the miner. He ought also to know that high candle-powers “ in the beam ” can be got from an oil lamp fitted with a bulls-eye ; in fact, with a bulls-eye fitted very loosely to a miner’s oil lamp to-day we easily read 6-candle power, but with a bulls-eye properly focussed it would no doubt be an easy matter to get 10- or 20-candle power “in the beam ” from our flame lamp, so that Mr. Joel’s figures of candle-power in the beam for the electric lamp are of no special credit to the electric lamp, and if the miners’ electric lamp is increased in weight, as Dr. Llewellyn suggests, I pity the poor miner. Mr. Joel is evidently not very familiar with the conditions down the mine, otherwise he would not make so much ado in regard to the fancied defects of the flame lamp. From the previous correspondence, he has owned up his knowledge that the combustion tube type lamp is of high candle-power; why, therefore, does he keep talking of 0‘3-candle power when he knows there is a practicable lamp with a light so very superior to 0 3- or 0 5-candle power. As a matter of fact, in the latest forms of the Hailwood combustion tube type lamp (whilst it gives over 2-candle power), we are, for forms’ sake, prepared to guarantee that it will give from 1J- to IJ-candle power, not only at the commencement of the shift but at the end of the shift, and day after day, not only for this year, but for this and next year and the year following and the year following that, and so on; and we would like to know where there is an electric lamp maker who can give this guarantee, from a lamp not weighing more than 3J lb. As regards the temperature, the figures given by Mr. Joel are somewhat over-aweing until one realises the fact that the total heat given out by a thousand miners’ oil lamps in one hour does not exceed that given out by one-third of a bucket of coal burnt in an hour, and if this was used as heating apparatus for heating up works with an equal area to that of a pit, I am afraid there would be a lot of complaints as regards its heating abilities, and when one takes into account the large amount of air passing through a pit, the heat given off by a thousand lamps seems too absurd to talk or think about. Probably Mr. Joel has overlooked the fact that whilst the flame lamp may be 120 degs. to 140degs. Fahr., the total area of the lamp as compared to that of the pit is infinitesimal. To show the importance of taking area, &c., into account, I think I need only refer to the fact that the filament of an electrical lamp when incandescent will probably be within the region of 2,700 degs. Fahr. As regards the amount of carbonic acid produced by lamps, we find that the total carbonic acid gas given off by 500 miners’ lamps does not exceed 2J cubic feet per minute, and anyone who cares to go to the trouble of dividing this into the hundreds of thousands of cubic feet of air passing into the pit per minute will again see what a ridiculously low percentage this carbonic acid gas works out to, and how impossible it is to have any effect on the health of the men, especially seeing that Dr. Harger has stated that it is not until 6 per cent, to 8 per cent, of carbonic acid gas in the air is reached that toxic symptoms appear, and that as much as 25 per cent, is needed to cause actual danger to life. If the quantity, viz., 2| cubic feet, of carbon dioxide is dangerous spread over a thousand men, the writer is beginning to have a nervous kind of feeling in regard to the carbon dioxide he swallows each day when drinking serated water, as one bottle of aerated lemonade would no doubt contain a goodly quantity of carbonic acid gas (CO2, carbonic anhydride or carbon dioxide, which are synonymous terms.) E. A. Hailwood, Manager for Ackroyd and Best Ltd. Morley, near Leeds, March 17, 1914. [This correspondence is now closed.—Eds. C.G.'] Experiments on Surface Combustion.—Prof. W. A. Bone read, at the meeting of the Royal Society last week, a paper by Mr. Harold Hartley on “ The Electrical Condition of a Gold Surface during the Absorption of Gases and their Catalytic Combustion.” At a recent meeting of the Royal Institution, Prof. Bone showed that by bringing coal gas or other combustible gas into close contact with oxygen by passing them through a porous substance the gases combined without flame, producing intense heat, which could be communicated to a boiler, or used in other ways, practically without there being any loss. The explanation of the result was that the gases under these conditions showed a very much greater affinity for each other. The research described was an attempt to determine on what this affinity depended, and also to investigate exactly what occurred when a gas was absorbed by a metallic surface. The first result found was that the metal under experiment, gold, was charged with negative electricity when the gases were burned in contact with it, and that the effect was primarily due to the absorption or “ occlusion ” of the gases. Further, the metal became negatively charged during the occlusion of the gas that was burned, the charges varying from 1-j- to | volt, while it was positively charged to f volt when oxygen was occluded. Lastly, it was argued that these electrical effects were probably due to the gas that was leaving rather than that which was entering the surface of the metal. These results are of considerable interest, as indi- cating that the efficiency of surface combustion is due to the electrification of the reacting gases, and from the theoretical point of view because the electrification of the gases when thus absorbed is an entirely new observation. They also support the view that the electrical effects seen in connection with incandescent solids is probably depen- dent on the occlusion of gas.