172 THE COLLIERY GUARDIAN. January 28, 1916. GAS DETECTOR FOR MINERS’ SAFETY LAMPS. By T. J. Thomas. The a-ttachpient illustrated in the drawings has been designed with a vie w to placing miners’ electric safety lamps on the same footing as (oil) flame -safety lamps in regard to the detection of meihane (firedamp) in mines. By means of this attachment -the light of the filament lamp is cut out in presence of firedamp approaching a dangerous percentage in the air, between the limits of 2 to 6 per cent. It may possibly also be utilised for the detection of carbon monoxide in dangerous quantities to human life. The principle upon which it depends is the well-known catalytic action which takes place when heated platinum is brought into contact with hydrogen or hydrocarbon gases. For the detection of other com- bustible gases -it depends upon the heat of combustion produced by burning the ga-ses suitably by means of platinum in wire or other form. The same attachment may be used for both purposes. A piece of platinum, in wire or other form (fig. 1), is mounted in series or parallel with the filament of the electric lamp, and the current is so passed as to heat this wire,to. the temperature necessary to -set up the catalytic action, or the combustion of the gas. When the platinum and filament lamp are connected in series, and tho lamp is brought into an atmosphere of firedamp, the 'effect is to reduce the light of the filament lamp in consequence of the platinum becoming heated and offer- ing. greater resistance to the passage of the electric current than before. If the lamp is kept for a prolonged period in an explosive mixture or one containing a high percentage of gas, the platinum wire becomes fused, and thereby breaks the circuit. A similar effect is produced by the lamp being kept in contact with analogous mix- tures of other combustible, gases and air. If connected in parallel, the effect would be that more current would pass through the filament lamp, thereby increasing the intehsity of the light when in con. act with firedamp or other combustible gases. In this case, the light is cut o,ut by the action of mercury, or other suitable metal or liquid,, owing to increased heat produced by .he catalytic action or combustion of the gases. Operation of Cut-Out Arrangement. If there is a mixture of firedamp and air around the lamp, the temperature of the platinum wire is raised (varying with the percentage of gas present). This increase in heat is, of course, communicated to the ther- mometer-like arrangement. The mercury expands, and completes the electrical circuit between the + and — in conjunction wi;h the passage of electricity. The wire is subjected to. three actions at. the same time :—Heat, electrical and catalytic. Very little appears to be known as to the actual causes of '.he change. The author proposes to overcome the difficulty by making provision for testing the resistance of the platinum wires in the lamps, and changing such as are found to be unsuitable. This testing and changing (when required) can be effected quickly and cheaply. Fig. 2.—General View of Testing Apparatus. . action of the heated wire. A sufficient margin of temperature is allowed for, and the heat of the wire is sufficient to prevent the cut-out from being affec.ed. Mention is made of this, because a device of this kind has already been brought out, in which the neglect of this factor appeared to render the lamp unreliable, in detecting gas. Another factor which will affect the wires of indicators which depend upon the catalytic action of platinum wire in hydrocarbon gases, is the effect of oxidation of the wire owing to the latter being heated all the time the lamp is in use, as in the case of the present detector. This oxidation increases the electrical resist- ance of the wire, since it decreases the diameter and cross-sectional area of the metal. This difficulty can be met by changing ;he wire when required, and will ba discovered .and rectified when the platinum wire circuit is tested for .resistance. The device is fitted with a small inspection glass for examining the wire during use, and the user will soon know, by experience in examining the wire, if the device is in perfect working order. The chief point in connection with the device is that it will cut out the light of the lamp before the amount of firedamp pre-sent is sufficient to form a dangerous mixture. Consequently, it -raises considerably the factor of safety -in the use of electric safety lamps. Elerftric lamps and oil flame safety lamps -are -sometimes used together in -tho working places, the oil lamp chiefly -as a gas indicator. In the case of a man ripping on the roadway, where lamps are being used in this manner, the possibility arises -that, after finding gas with an oil lamp, he may use -the eleciric lamp, for lighting the place, by hanging it up in the gas and going on with his work. This he could not do if oil lamps alone were u-sed, as the lamp would not give any light in an atmosphere bordering on an explosive mixture of gas and air. In tho circumstances under consideration there would be a danger of igniting the gas if tho filament lamp were to be damaged by -the pick or tool. If, how.-ver, the electric lamp were provided with tho author’s device, the latter would cut out the light and prevent the user continuing work, except in darkness. Owing to absence of a suitable device of this kind, colliery owners and managers, as a rule, prefer to use oil and electric lamps jointly, though it Is understood that one particular colliery has electric safety lamps in use by the workmen, whilst the officials use flame safety lamps for testing the air for the presence of firedamp and other noxious gases. If electric lamps are introduced -into a colliery on the score of safety -alone (apart from -increased light) the simultaneous use of gauze (oil) safety lamps (for testing, etc.) defeats this object, since i-t makes the actual safety Mercury Mercury Cut-Out Arrangement Attached to + Contact of Lamp Platinum Wire + Contact -(■Contact I —Contact Platinum Wire — Contact OR Body of Lamp O Spring Lock Nut-7,.. + Contact Resistance Wire □--Porcelain Insulator .-Conductor ---Insulator Insulator S wiiht Voltmeter Ammeter Filament Lamp Plug Plug Platinum Wire Arrangement Switch (to platinum wire) Fig. 3.—Arrangement of Circuits in the Testing Apparatus. Fig. 1.—Method of Operating the Cut-out Arrangement. (The wire will pass down the capillary tube to a certain point.) poles of the cell by joining up the wires. The wire attached to the plus contact is of sufficient resistance to complete the circuit without damaging the cell by- running it down too quickly. Its effect- on the lamp is to cut out or reduce the light of the filament lamp sufficiently to give an unmistakable indication of the presence of gas to the user, and to reduce the light of ■ the lamp so as to make it useless for carrying on his wprk., When the mercury contact arrangement is in operation, three paths are open to the current from the coll : through the filament lamp circuit, through the platinum wire circuit, and through the mercury cut-out arrangement. When these three circuits are closed, there is hothirig in the lamp capable of igniting gas, should either the filament lamp or the platinum wire arrangement be damaged. Devices embodying these principles have been tried in the form of different kinds of apparatus, but in practice they have been found troublesome and liable to give misleading results. Some of these difficulties will now be enumerated, together with the manner in which it is proposed to overcome them in -the new gas detector. In the first place there is a danger of the platinum wire becoming fused in some forms of apparatus owing to the quantity of electric current being much too great for -the platinum ware to carry, the wire being unable to with- stand the inte-n-se catalytic action produced, and fusing on account of the high temperature produced by both caiises. The . author experienced no difficulty in this direction in his method of using the platinum wire (sec results of tests). The crux appears to be the alteration in electrical resistance of the .platinum wire due -to the catalytic action of the gas on the wire; possibly this may be attributable to the catalytic action itself, or to the violent changes of temperature to which the wire is subjected by tho varying amounts of gas, or -to both these causes The probable cost of the wire in the platinum w-ire arrangement proper would be about 0’125d., so that if the wire had to be changed once a week, or possibly every day in special cases, this difficulty would not be insuperable. As a matter of fact, miners’ lamps (apart from firemen’s lamps) are seldom exposed to a mixture of 2| per cent, of gas, let alone an explosive mixture, so the cost on this score would be almost inappreciable. The value of the platinum as a metal is not depreciated, and its sale will partially cover the cost of renewals. In some cases in existing forms of gas detector, the change in the resistance of the wire has been found so con- siderable, even after one round of tes.ing in a mine, that the zero on the scale could not be re-adjusted accurately even in pure air. No similar difficulty is to be antici- pated in the case of the new device when attached to a fireman’s lamp, for the following reason. The current in apparatus in which a magneto battery is employed is very irregular, and sometimes causes very -high temperatures to be attained, even to the extent of fusing the platinum -wire in presence.of gas. Now the current from an accumulator cell is fairly regular (the voltage falling 10 per cent, during use), so -there should be -very little trouble on that score. Another point to which attention has to be given in these electrical detectors is the drop in vol', age of the cell, which, as stated above, is about 10 per cent. The author has given close -attention to this matter, as the increased temperature produced by the wire, when in presence of gais, actuates the cut-out. If this poin: were neglected, the platinum wire might -not be raised to a sufficient temperature to star: the catalytic action and combustion, and therefore the apparatus would be use-- less, and even dangerous. With regard to the differences of temperature in different parts of the mine, the cut-out is -so designed as not to be affected thereby, but to cut out solely by the of the mine dependent upon the gauze lamps all the time, the latter, for testing purposes, being poked into all the places likely to contain gas, and therefore dangerous. The question whether an -increased factor of safety is really obtained by the use of electric safety lamps is a moot point, for there are certainly still a number of features in which these lamps seem capable of improve- ment. For instance, a dangerous material, celluloid, is used in the construction of the cells, which are usually charged with sulphuric acid. In this connection, a matter for serious consideration by mine owners and mining engineers arises, namely, what might probably happen if a large number of electric lamps in a mine were blown to pieces by an explosion of firedamp or coal dust, some of them at a point reached by -the force of the explosion alone, and not by the flame. Is there a possibility of the celluloid becoming ignited and starting a fire in the mine; and what igniting effect would the mixture of sulphuric acid and water originally contained in the cell have upon coal dust, timber, or brattice cloth under these conditions? It is a curious fact that it took the users of the Davy lamp from 1816 to 1833, 17 years, -to discover that this lamp was not safe under all conditions in mining. At present, miners’ electric safety lamps a-re being introduced largely into mines, and it is to be hoped that if any defects exist in regard to their safety, these will be discovered and remedied before -a period of .1.7 years has elapsed. Testing Apparatus. The apparatus (fig. 2) by means of which the experi- mental tests (the results of which are given below) were carried out, consists of one 4-volt six ampere hours Clifton accumulator B C 1 . . . .; one 2-volt 12 ampere hours Fuller (patent) block accumulator type M.L.; one Osram 0-8 ampere filament lamp; a. regulating, resist- ance; and three switches. A glass cylinder, open at