1070 THE COLLIERY GUARDIAN. May 15, 1914. __________________________________________________________________________________________________________________________ (b) Porch Lamps. Porch Safety Lamp No. (010) P. The Porch Safety Lamp No. (010) P, the general design of which is shown in fig. 28, is a double-gauze, flame, oil lamp, with air inlet holes through the middle ring. It consists of the following essential parts :— (1.) Ponnet or Shield of seamless or riveted steel, with a separate securely fastened crown. Furnished with outlet holes round the top: provided that the bottoms of the holes are not less than f in. above the top of the outer gauze. (2.) Middle Ling, of brass, steel or iron, riveted to the bonnet, provided with vertical air-inlet holes of total area not exceeding 1’4 square inches. Pillars, of brass, steel or iron, four or more, fitted or not with securely fastened pillar guards. Bush or Bottom Bing, of brass, steel or iron. (3.) Gauzes of not less than 28 S.W.G. steel or best char- coal annealed iron wire, 784 meshes to the square inch, with secure flametight double-folded lap seams, or single-fold seams secured by iron strips, formed to fit flanges of the inner and outer base rings. The arrange- ment of the gauzes is such that the gauze rings form the seating necessary to hold the glass firmly in position when the retaining ring is screwed home. Internal dimensions. Outer gauze. Inner gauze. Height from shoulder) . ( +4 in.) _ . , of the base ring J 5< 1D-[-hnj 5 Diameter at top..... 2T% in. in ...Ijf in. ±|in. Diameter at bottom ... 2^ in. ±|in....2/g in. ±|in. (4.) Glass:— External diameter ......... 85 mm f + ? mm* (. 1 mm. Height .............................. 90 mm. + | mm. Size mark................. 85-90,or A.B. 1 P. (5.) Glass Retaining Bing, of brass, screw-threaded to fit the bottom ring. (6.) Oil Vessel.—A casting of brass, or of stamped steel or brass, with a securely fastened brass top ; fitted with a flat 1 in. burner. Fig. 28.—Porch Safety Lamp No. (010) P. (Ackroyd and Best Limited.) ■UTT L (7.) Locking Device.—A lead-rivet lock of one of the types shown in fig. 28, and in “ The Safety Lamps Order of the 26th August, 1913.” (8.) Beflector.—The lamp may be fitted with an overhead reflector as shown in fig. 28. The lamps are made at the works of Messrs. Ackroyd and Best Limited, at Morley, near Leeds. The lamp shall be used only within the following limits :—(a) On main intake airways and haulage roads ventilated by intake air up to within 300 yds. of the first working place at the working face which the air enters; (b) on main return airways within 300 yds. of the bottom of the upcast' shaft if that shaft is regularly used for the purpose of winding persons or minerals but not within 300 yds. of the last working place at the working face which the air leaves. The Davis-Porcas Lamp. The Davis-Porcas Lamp, the general design of which is shown in fig. 29, is a double-gauze, flame, oil lamp, with air-feed through vertical holes in the middle ring. It consists of the following essential parts :— (1.) Bonnet or Shield, of riveted steel, furnished with outlet holes near the top, so arranged that the bottoms of the outlet holes are not less than |in. above the top of the outer gauze. The bonnet is removable, and is locked to the crown by a lead-rivet lock. (2.) Crown, of brass, steel, or iron, supported by three steel or iron upper pillars. (3.) Middle or Bonnet Bing of brass, riveted to the bonnet, furnished with vertical air-inlet holes of total area not exceeding 3'0 square inches. Pillars, of brass, steel or iron, five. Bottom or Lock Bing, of brass. (4.) Gauzes of not less than 28 S.W.G. steel wire, 784 meshes to the square inch, with double folded lap seams strengthened by a steel liner, formed to fit flanges of the inner and outer base rings, and so secured to the same by folding joints as to make strong and flametight joints. The arrangement of the gauzes is that shown in fig. 29. Internal dimensions. Height from shoulder of hoop ................ Diameter at top ........ Diameter at bottom .... Outer gauze. Inner gauze. 6 in. ± 4 in. ... 5|in. ± 4in. 2y in. ± | in. ... 2|in. ± 4 in. 34 in. ± 4 in. ... 2|in. ± Lin. (5.) Glass, fitted or not with loose brass end-rings. External diameter.......... Height ____________________ Size mark_________________ 914 mm. 103 mm. + 0 mm. — 1 mm. ± 4 mm. 914-103 orSIVAD4. Fig. 29.—Davis-Porcas Lamp. (John Davis and Son (Derby) Limited.) (6.) Glass Betaining Bing, of brass, screw-threaded to fit the bottom ring. (7.) Oil Vessel.—A solid casting of brass with a securely soldered brass bottom ; fitted with two flat | in. burners, fitted with a shield, as shown in fig. 29, when burning mineral oils. (8.) Locking Device.—A lead-rivet lock with a hasp or lug securely fastened to the bottom ring by a sliding band, or otherwise, or to a pillar, and a staple or lug securely soldered to the oil vessel. (9.) Beflector.—The lamp may be fitted with a removable reflector. The lamp is made at the works of Messrs. John Davis and Son (Derby) Limited. The same condition is attached as in the foregoing instance. Both these lamps are to be capable of main- taining a light of not less than O'75-candle power all round in a horizontal plane throughout a period of not less than 10 hours. _________________________________ 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. ________________ THE SCHOELLER MINERS’ LAMP GAS DETECTOR. Sir,—Your article on the above is full of interest to all practically interested in the detection of gases in mines. I note that you state that the demonstrator breathed fresh air' into the instrument, and thus obtained a reading in the reverse direction. I pre- sume that your meaning is ordinary expired air (CO2 + 0H2 + N), but free from CH4 or H, in which case the effect would be the same as with an Ansell or any other single chamber diffusion instrument. The result would be a mixture of air and C02 and 0H2 inside the chamber. It would, however, interest engineers to hear from Mr. Schmahl the indication obtained during his underground tests with consecutive readings in a gassy atmosphere, the first reading being taken at say 70degs., and the second reading close to compressed air tools coated with snow—the temperature inside the diffusion chamber being that of the lamp chamber. As a matter of physiological fact, CH4 is given out by the breath'about as freely as it is inspired, but no doubt some method has been found by the inventor to obviate any difficulties from these sources. A little thought will, I think, make it apparent to any physicist that the following conditions are essen- tial for reliable readings with diffusion instruments :— (1) An apparatus where the interior atmosphere is of constant density relatively to the gas to be tested and so constructed that the expansion and con- traction due to temperature and pressure changes do not affect results. (2) A porous medium of constant porosity, unaffected by dust and moisture. (3) A fluid index with constant surface tension, mobility, quantity, and weight. (4) A U-tube of constant capillary and surface friction. If, after a reading when CH4 or H is left in the diffu- sion chamber, and the pressures have equalised to the normal, a test is taken in C02, the reading would be a different one from when the chamber contains air only —which is true of a test of external CH4 with CO2 inside. The manometer indication depends upon the rate of egress of internal atmosphere as well as upon the ingress of the external atmosphere. We shall be pleased to hear further on these points, and also why the opening of a valve and letting in the atmosphere of the mine does not vitiate succeeding tests of the air outside the instrument — through the extended courtesy of your columns. Fred J. Turquand. Albion House, 59-61, New Oxford-street, W.C., May 11, 1914. _____________________ THE SENGHENYDD EXPLOSION. Sir,—It is somewhat surprising and very disturbing to those of us who are either directly or indirectly responsible for the safe working of collieries to learn that H.M. Chief Inspector is of opinion that “ sparks ” caused by rock stones striking each other when heavy falls occur, are capable of igniting an explosive atmo- sphere of firedamp and air. (See Official Report.) The Inspector also states that sparks of this character ‘ ‘have been known to originate explosions.” Would any of your readers, who may have studied this subject, tell us what evidence there is that the inspector’s views are sound or otherwise. Henry Hall. May 11, 1914. IGNITION OF EXPLOSIVE MIXTURES BY ELECTRIC SPARKS. Sir,—A good many years ago, it may perhaps be remembered that I made a long series of experiments upon this subject. I think it is well known that I pioneered electrical signals pretty well all over the United Kingdom; and from time to time the question would come up, whether it was dangerous to fix them on engine plane roads, where there was a possibility of gas. I was also called in as an expert, in connection with an explosion of petroleum vapour, which took place on board a ship in a dry dock at Newport; and made a considerable number of experiments in connection with that. What I found was, that it was not a spark per se, nor a particular voltage, that exploded gas. This, of course, has long since been confirmed. I found that it was the delivery of a certain quantity of energy, which might be either in the form of a spark, or in the form of a heated wire, or heat in any other way, which caused ignition. I found also that the amount of energy required for ignition of an ordinary mixture of towns’ gas and air, was 10 watts. It is now, I think, well known that mixtures of methane and air are much less sensitive to ignition than towns’ gas and air. The curve which Dr. Wheeler gave, showing the easier ignition of methane and air when the percentage of methane was between 8 per cent, and 9 per cent., has also, I believe, been well known for a good many years. Sydney F. Walker. Bloomfield-crescent, Bath, May 11, 1914. _________________________ THE HAILWOOD COMBUSTION TUBE OIL LAMP. Sir,—With reference to the article in your esteemed journal of the 1st, in which you refer to the Belgian decree of December 6, 1913, not having covered the combustion tube lamp; it appears from questions which have been addressed to me it is possible that doubts may exist in the minds of other of your readers, as to whether this is intended to imply that the lamp failed to pass the Belgian test. I should be glad to have an opportunity of explaining that when the Belgian decree was issued on December 6, 1913, in reference to the Hailwood lamp that the combustion tube had not then been put forward to the Belgian Government, and in fact was only quite recently sent to them, and in the preliminary tests (which are very similar to the final test) it gave such very satisfac- tory results that it is now being submitted by the Belgian Government to the final severe tests, and there is not the slightest indication of its failing to pass these tests, but on the other hand everything tends to show that it will meet with the highest approbation. M. Lemaire was delighted with its extraordinary high candle power, and extraordinary safety in explosive mixtures of gas travelling at even the highest velocity. E. A. Hailwood. Morley, near Leeds, May 6, 1914. ______________________________ Sheepbridge Coal and Iron Company Limited. — Lord Aberconway presided on Wednesday at Sheffield over an extraordinary meeting of the shareholders, held for the pur- pose of confirming resolutions passed a fortnight ago whereby the capital of the company is to be increased to <£1,250,000 by the creation of 450,300 ordinary shares. The resolution of confirmation was carried unanimously on the motion of the chairman, seconded by Mr. Deacon.