Lighting Underground Mine & Illumination

Lighting Underground Mine & Illumination

In preparing this paper the object has been to set forth facts relating to lighting or illumination problems faced in underground mines, which, judging from the results realized in the iron and steel and other industries somewhat similar to mining, will tend toward furthering safety, production, and contentment of employees, as well as economy of operation in mines. By applying the principles of illumination with the assistance of modern appliances, the full benefits in efficiency may be derived from improvements already made in other details of mine operation.

The lighting of a typical coal mine may be divided into four distinct parts:

  1. 1, The lighting of the buildings about the top;
  2. 2, the lighting of the working faces;
  3. 3, general illumination at the bottom; and
  4. 4, special applications of lighting.

The lighting of buildings about the top may be treated in the same manner as that of any other industrial plant, for we have a boiler room, an engine and generator room, a forge, a machine shop, and a hoist room. These can be well and efficiently lighted by the use of 100-watt tungsten-filament multiple lamps with proper reflectors so spaced and suspended that a power consumption of from ¼ watt per square foot in the boiler room to 1 watt per square foot in the machine shop is obtained. The methods that apply to this kind of lighting have been ably treated by a number of authors, and for this reason a detailed discussion is unnecessary.

The lighting of the working faces is usually done by means of portable lamps, of which there are four types in use: The oil torch, the acetylene lamp, and the oil and the electric safety lamps. The different types have been fully described in numerous papers and articles and will not be covered here, although a few figures on the cost of operation will no doubt be of interest. In attempting to obtain cost figures, one is impressed with the fact that apparently very few such data have been obtained in this country. It would seem that such data would be of particular benefit at this time, with the advent of the electric safety lamp.

The oil torch is without question the cheapest source of light. The acetylene lamp, at a cost of 6c. to 10c. per lamp per week, gives far superior illumination, but the characteristics of this source of light as well as any other open-flame lamp will bear careful consideration in view of the ever present desire for industrial efficiency and safety. It is the opinion of many that the greater percentage of disastrous explosions in this country have resulted from the use of open flame lamps in the so-called non-gaseous mines. This question of safety, of course, merits serious consideration.

The oil safety lamp has a distinct advantage in that it gives an indication of the presence of gas. Its development marked one of the greatest advances in mine lighting, although in most cases at the present time it is not considered a guarantee against explosion when in the presence of gas. Figures obtained from foreign countries indicate the cost of using oil safety lamps is from 7c. to 9c. per lamp per week.

The electric lamp gives a steady and readily directed light, free from gases, soot, and frequent outage. A large proportion of the generated light is directed on the working face. It is sometimes considered a disadvantage that the electric safety lamp does not give an indication of gas as does the oil safety lamp. The trend of opinion in England, however, is toward choosing a lamp for the light it gives and the use of some other means for gas indication. There is no question that an electric lamp passing the tests of the U. S. Bureau of Mines will give more light on the working face than any of the three previous illuminants, because it has been scientifically designed with that end in view.

Foreign practice has shown that electric light costs from 12c. to 17c. per lamp per week. This cost is about twice that of the oil safety lamp. The light on the “face,” however, is materially increased by the use of the electric lamp. One foreign electric-lamp manufacturer places the cost of electric light at 2½c. per lamp per shift. This figure, though it seems low, can well be realized in this country with a large installation, and proper care. In this connection, it is very necessary to have proper housing and proper attention for electric lamps—more so than with the oil safety lamps. It has been found in foreign practice that this care and attention is very little, if any, more expensive than the attention that is given to oil safety lamps, even though more expensive help is needed, because fewer men are required to care for the electric outfits. This country has been slow in taking up the electric lamp. It has been said that in Belgium alone there are 12,000 outfits in use. The excellent work done by the U. S. Bureau of Mines to obtain the highest efficiency for this new source of illumination has accomplished what years of competition among electric mine-lamp manufacturers could hardly have brought about.

The application of the principles of industrial illumination to the general lighting of mines must be made in the face of conditions difficult to overcome. In fact, all the conditions the illuminating engineer considers most


difficult are present: low ceilings, black walls, dust, smoke, and dampness; but in spite of these, very satisfactory results have been obtained.

An ordinary mine, from a lighting standpoint, can be considered as composed of at least six parts: the bottom, the run-around, main entry, side entries, mule stables, and small rooms, such as offices, pump rooms, storage rooms, and first-aid rooms. These are shown diagrammatically in Fig. 1. The bottom, being the entry and exit for both men and coal, accommodates more traffic than any other part of the mine and should be especially considered from the standpoint of both convenience and safety. Fig. 2 shows a portion of a well-illuminated bottom and shaft opening of a typical mine. The lighting of the shaft in this case was accomplished by the use of 40-watt tungsten-filament lamps equipped with angle reflectors, placed above and across the shaft opening so as to direct the light on the cages. The maximum intensity is at the near edge of the cage, and the eyes of the workmen on the side of the shaft toward the observer are not subjected to the glare of the lamps. For comparison, Fig. 3 shows this same portion of the mine lighted by the use of bare carbon lamps. It is



readily seen that the distribution is not of the best and also that the glare of the bare lamps obscures that portion of the mine which lies beyond. These illustrations were made from actual photographs, retouched only enough to remove the halation effects of the bare lamps. The photograph shown in Fig. 2 was exposed about 1 min. as against 15 min. for the one in Fig. 3.

That portion of the bottom leading into the mine, where cars are directed on to the cages, can be well lighted with 40-watt tungsten lamps in shallow dome reflectors placed above and between the tracks. These units, spaced at about 6-ft. intervals and hung about 8 ft. above the floor, will give satisfactory distribution of light. It will be noticed from Fig. 4 that the car wheels are well illuminated and that there is practically no glare. It would be well to design the lighting of this part of the mine on a basis of 4 to 5 foot-candles at the floor, not because the work demands this intensity, but because of the greater safety which results from ample


illumination and because dust collecting on the lamps and reflectors decreases the amount of light delivered.

The run-around should require only sufficient light to make visible any obstructions in the path of the empties as they leave the cages. This part of the mine may be illuminated with 25-watt tungsten lamps equipped with shallow dome reflectors, spaced 15 ft. apart and suspended 8 ft. above the floor. In the main entry, the function of light is not so much to illuminate as to silhouette objects which may obstruct the passageway. With silhouette lighting, a comparatively small amount of light is needed to obtain the effect desired, which is to see objects outlined against something that is lighted. For instance, whitewashed doors or walls reflecting the light toward the observer’s eye are excellent backgrounds against which objects form silhouettes when in the line of vision of the observer. The glint of the light on the rails forms another good surface from which silhouette lighting may be obtained. With 25-watt tungsten lamps in shallow dome reflectors, spaced at intervals of about 300 ft., the height depending upon the height of the entry, the silhouette lighting is excellent. Two units, one to illuminate the switch and the junction and the other illuminating a portion of both the main and side entries, help to eliminate
collisions and by the increased light warn the trip driver that his train is approaching such a junction.

The mule stables with their low roofs may be effectively lighted with 40-watt tungsten lamps equipped with angle reflectors placed along the back wall and as high as possible, one unit to each two stalls. In front of the stalls and opposite the angle units, 25-watt tungsten lamps with deep bowl reflectors may be used to illuminate the feed boxes and passageway.

The mine offices need but one 25-watt tungsten lamp equipped with a shallow dome reflector. The fireboard at the bottom should be well illuminated with one or more 25-watt lamps of this type equipped with angle reflectors, depending upon the size of the board, while the pump rooms and storage rooms may be lighted in the same manner as offices.


The first-aid rooms, in order that the best attention be given the injured, should not only be well lighted, but should have the walls well white-washed, thereby obtaining well diffused and distributed light. Frequent whitewashing of the walls of the bottom, offices, mule stables, etc., and the walls of the entries for 20 ft. each side of the units, will greatly increase the illumination in these parts of the mine. Carbon lamps are most generally used in mines, but to keep the load on the generator as low as possible and maintain the most constant illumination in spite of voltage fluctuation, and to direct the light where wall and ceiling reflection cannot be relied upon, tungsten-filament lamps with weather-proof enameled reflectors will, in my opinion, be found most satisfactory.

It may be interesting, by reason of the high voltage usually found in mines, and its fluctuation, to show how the proper voltage for a lamp, to secure greatest life and light, is determined. A recording voltmeter is connected at the switchboard on the terminals of the switch controlling the lighting circuit, usually the trolley line. When this is in operation, a carefully calibrated portable voltmeter is connected in multiple with the recording meter and a section of the chart of the recording meter is compared with the readings of the calibrated portable meter. Fig. 5 shows a section of such a chart and the calibrated line. This chart should be taken over a period of at least 3 hr. and for 24 hr. if possible.


Voltage readings are then taken back from the shaft along the main entry at intervals of 300 or 400 ft. by means of the portable meter, the voltage and time being recorded. A study of the chart will show the average voltage over the period taken. A comparison of the chart with the voltage readings taken back in the mine will show the average drop in the line. From the average voltage obtained from the chart should be subtracted the average line drop obtained from the readings taken in the mine, the result being the voltage on which lamps will operate to give the same life as on the fluctuating voltage in the mine.

For average voltages up to 250 volts, regular multiple lamps should be used. For average voltages from 250 up to 280 volts, there is a choice of burning lamps in multiple or in series. The best practice is to burn two lamps, carefully selected, for current, in series. Such lamps can readily be obtained and are known as street-railway lamps. For voltages above 280, the proper lamps should be selected for series burning. Table I lists lamps for specific voltages.

A recording chart, used as described previously, showed a maximum voltage variation of 20 per cent. From Fig. 6 it will be seen that with a 10 per cent, reduction in voltage, the candlepower of the carbon lamps is 20 per cent, lower than that of the tungsten lamps. Fig. 6 shows that the characteristics of the tungsten lamp are such that voltage variation does not affect candlepower as much as it does that of carbon lamps.

candlepower characteristics of incandescent lamps

A few comparative cost figures in connection with the problem of more efficient illumination follow. Consider, for example, an installation, such as illustrated in Fig. 1, where twenty-six 40-watt tungsten lamps and reflectors and thirty-one 25-watt tungsten lamps and reflectors are to replace the same number of 32-cp. and 16-cp. carbon lamps, respectively. During a period of 300 days, at 10 hr. a day, the tungsten lamps would consume about 5,440 kw-hr., while the carbon lamps would consume about 14,940 kw-hr. With the cost of current at 0.5c. per kilowatt-hour, the saving in cost of power with the use of tungsten lamps would be about $50 a year. From this must be subtracted about $17 for the difference between the cost of the carbon lamps and the tungsten lamps. This will leave about $23 net saving. With the reflectors costing $60, the installation would be paid for in three years.

These figures tend to show that if dollars and cents alone were considered, it would be more profitable to use the higher efficiency lamps. This is even more marked when the illumination on the working plane is considered, because with the use of reflectors the illumination is more than double that obtained with carbon lamps.

There are many other places where special applications of lighting would tend to increase efficiency and convenience; for instance, trip-lights—now as a rule simply oil torches on the end of the train—could be easily replaced by small storage-battery outfits showing a red light. Locomotive headlights can be equipped with low-voltage concentrated-filament tungsten lamps in parabolic reflectors, with a decrease in trouble, increased light, and decreased breakage over the present carbon or regular tungsten filament. Two 30-volt, 100-watt tungsten-filament locomotive-headlight lamps can be burned in series with a resistance. The loss in current through the resistance is a small factor as compared with the gain in steadiness and brilliancy of illumination from the parabolic head-lights. The construction of this lamp is such that maximum strength of filament is obtained, which is an essential feature where the service is as severe as on a locomotive. Another possible consideration is the placing of distinctive lights where telephones are located, or where first-aid equipment may be obtained. This could be accomplished by the use of red lights on the power circuit installed in connection with a small primary-battery system, which would operate a miniature lamp in place of the large lamp should the power circuit for any reason fail. This system has been successfully worked out in theaters where the same principle is involved.

It is hoped that, from the few figures given in this paper, it will be seen that the application of the latest scientific knowledge to the lighting of mines is not so expensive as it is generally thought to be, and should be considered as a means of increasing safety, bettering working conditions, increasing production, and at the same time decreasing the cost of operation.


Edwik M. Chance, Wilkes-Barre, Pa.—I have been very much interested in the comprehensive and able discussion of the important topic of mine lighting just given by Mr. Burrows, especially as I know by common report Mr. Burrows’ ability and his close touch with the development of the electric mine lamp, and its use in mines in connection with a portable electric lamp. It is regrettable that Mr. Burrows was not able to acquaint himself more closely with the cost of mine illumination, the actual cost, as produced by a portable light as carried by miners, whether a flame safety lamp or an open light. Had he been able to acquaint himself more closely with these data, he perhaps would not have arrived at some of the conclusions which he has presented to us in his paper. For example, we find Mr. Burrows advises that the open torch is by far the cheapest source of illumination, as produced by a portable light. I am very sure that is not the fact. The cost of miners’ oil varies from about 25 c. a gallon to 90 c. a gallon. The various States have passed laws from time to time rendering it mandatory that the miner shall use, whether he is willing or not, a so-called better or higher grade of burning oil. These laws have entailed the use of an oil so expensive that the use of the oil torch has become practically impossible, and the acetylene or carbide miners’ lamp has largely taken its place.

I have evolved a few figures showing the relative efficiency and usefulness of the open oil torch and the acetylene miners’ lamp. For example, the acetylene miners’ lamp consumes or burns 4 liters of acetylene per hour, or 0.14 cu. ft.; the oxygen consumed is 10 liters, or 0.35 cu. ft. per hour; air consumed, 50 liters, or 1.76 cu. ft. per hour; black-damp produced, 40 liters, or 1.41 cu. ft. per hour; air rendered extinctive to the acetylene flame, 112 liters, or 3.95 cu. ft. per hour; carbide consumed, 13 g. per hour.

The open oil torch, on the other hand, burns about 20 g. of oil per hour; the oxygen consumed is 48 liters, or 1.69 cu. ft. per hour; air consumed, 240 liters, or 8.47 cu. ft. per hour; blackdamp produced, 191 liters, or 6.73 cu. ft. per hour; air rendered extinctive to oil flame is 1,413 liters, or 49.92 cu. ft. per hour.

In addition to this, the acetylene lamp gives a much more accurate and reliable indication of the presence of blackdamp, for the reason that the oil lamp is too sensitive to blackdamp. The latter is extinguished if the oxygen in the air falls to 17.5 per cent. A man is able to live and work with 10 per cent, of oxygen, and a miner knows, when the oil lamp is extinguished, that he can still live in the atmosphere, and he will venture into regions where the air is extinctive to his oil torch, and be overcome, whereas with the acetylene lamp, the flame of burning acetylene is extinguished in still air when the oxygen falls to 12 per cent. At 14.5 per cent, the acetylene flame loses its brilliancy, becomes long and very blue, and the miner is given an indication of the presence of blackdamp in dangerous quantities. He knows that blackdamp extinctive of his oil lamp is not so dangerous as that extinctive of his acetylene lamp and if the acetylene lamp loses its brilliancy, he knows he is near the danger limit and will not enter further into the mine.

The illumination produced by the oil lamp has an intensity of about 2.5 cp. The illumination produced by the acetylene has an intensity of about 6, sometimes more, and sometimes as low as 5. The relative costs of these sources of illumination are about as follows: For the acetylene lamp per week of 54 hr., the depreciation charge is about 2 c. The cost of carbide is about 7.5 c., based on carbide at 5 c. per pound, and assuming a consumption of 1½ lb. of carbide per week, giving a cost per week of 9.5 c. In the case of the oil lamp, with oil at 45 c. per gallon, assuming that the lamp consumes 0.33 gal. per week, which has been found to be the average figure, this is a little low; the cost for oil is 13.6 c. per week. The cost of about one-half ball of wick cotton, which will be used in the wick during a week, is 2.5 c., making the total cost per week for the oil lamp 16.1 c., an increase over the acetylene lamp of 6.6 c. per week.

In addition to this, the cost for the acetylene lamp per week-candlepower is 1.6 c., whereas the cost for the oil lamp is 6.4c. per week-candlepower, showing clearly that the relative cost of the acetylene lamp and oil lamp is greatly in favor of the acetylene lamp.

This has been borne out in practice. I have yet to see the men of a colliery that has abandoned the use of the oil lamp for the acetylene lamp willing to return to the oil torch. In addition to this, the oil torch, because of the nature of the materials burned, produces a large amount of sticky soot and more or less offensive odor, which have been found to be very trying to the miners.

In regard to the use of the so-called electric safety lamp in mines, I will say that this usage is at present in its infancy. I believe in the very near future we will have mine electric lamps that are very much more satisfactory than those which have been used in the past.

There is no question but that this art is making rapid strides, as the author of the paper has so well stated, and that the Bureau of Mines has been especially active in promoting the improvement of these lamps.

Regarding the relative cost of the electric lamp and the oil safety lamp, I will not go into detail for the reason that the oil safety lamp is provided by the coal operator, as required by law, remains his property, and is maintained by him.

T. M. Chance, Wilkes-Barre, Pa.—(Demonstration with lamps).— I think I could not add anything in direct discussion of this paper, but the members of the Institute may be interested in some work we have done in attempting to produce an improved safety lamp.

The great difficulty experienced in safety-lamp lighting is the low illumination available in the present forms of oil-burning safety lamps. The candlepower of these lamps will vary from 0.15 for the original Davy lamp up to a maximum of about 1.60 for the latest type of Ackroyd and Best kerosene-burning lamp, which is obtained by the use of a reflector, the mean horizontal candlepower of this latter lamp being between 1.00 and 1.20 Standard English Sperm candlepower. While somewhat higher values than those quoted have been obtained with the Davy lamp, we have found the figures given to be about the average attained in practice (see Tables I and II).

photometer tests

The highest illumination that has hitherto been available is that reached in the Ackroyd and Best lamp. This lamp, which is made in England, burns 300° kerosene and gives a white flame of fairly intense illuminating power. The lamp is of the Muessler type with a small glass chimney fitted to the lower end of the Standard Muessler chimney, and completely surrounding the flame. This construction greatly improves the ventilation of the flame and the increased illumination is largely due to this improved ventilation. The principal defect of the lamp is that heavy jars, or falls, extinguish it, and to permit its efficient use it has been found necessary to install electrical reigniting stations underground.

One of the best types of liquid-fuel burning safety lamps used in this country is the benzine lamp. The Wolf lamp, built in Europe, and used generally in this country, is probably the most familiar type of benzine lamp in use. This lamp is of the Marsaut type with bottom air feed and possesses admirable qualities. The illuminating power of the lamp has been claimed to exceed 1.0 candlepower, but in our tests we have never been able to get so high a result. This lamp has the same defect, although to a somewhat less degree, as the Ackroyd and Best, i.e., ease of extinction. The Wolf people have overcome this trouble by the use of friction reigniters, either of the phosphorous match or Auer Metal type, a method of reignition of course impossible to use with a non-volatile fuel such as kerosene.

description of lamps tested

This use of internal reigniters has been the subject of much discussion. I understand that in West Virginia such igniters must be so made that the individual miner cannot relight his lamp but must apply to a mine boss or other official provided with a key for this purpose, and I believe a somewhat similar regulation has been proposed in England, as it has been thought that some otherwise unexplained explosions have been produced by careless reignition of lamps provided with such reigniters.

In endeavoring to produce a safety lamp of improved illuminating power we felt that the liquid-fuel burning lamps already develop about the maximum illumination that can be secured with these fuels, and as the candlepower of the portable electric lamp cannot be increased without a corresponding increase in the weight of the battery, it seemed to us that the most promising field for improvement was in the development of a satisfactory acetylene lamp.

A number of European investigators have attempted to produce a practicable acetylene safety lamp but these attempts have failed because of the ease with which the acetylene flame is extinguished by concussions from shot firing. These investigators attempted to overcome this

acetylene safety lamp

difficulty by the use of internal reigniters similar to those applied to the benzine lamps of the Wolf type, but such a method of reignition removes the lamp from the safety lamp class, because with manually operated reigniters of this kind, internal explosions may be produced in the lamp that will not only pass flame through the gauzes, but may even wreck the top of the lamp. This is due to the formation of explosive mixtures of acetylene and air in the time interval between the extinction of the flame and its reignition by the miner. The Belgian investigators at Mons made elaborate tests of acetylene safety lamps fitted with reigniters of this type and as a result of these tests the use of acetylene lamps with internal manually operated reigniter has been prohibited in Belgium.

It seemed to us that this difficulty could be overcome if a reigniter could be made that was automatic and instantaneous in action. This conception of the necessity for an automatic reigniter resulted in the production of the lamps shown in Figs. 1, 2, and 3. These lamps are Standard 5- and 12-hr. Wolf acetylene safety lamps in which the manually operated reigniter, noted by the ring “a” in Fig. 1 has been replaced by the automatic reigniter “b.” This automatic reigniter is in this case formed of a flattened coil of No. 20 nicrome (nickel-chromium


alloy) wire, placed between the flames of a two-jet burner. In operation the reigniter is heated by radiation from the flames, no portion of it being in contact with either flame. Immediately following the extinction of the lamp by concussion, the reigniter (which is red-hot) relights the jets as soon as the flow of acetylene through the burner is reestablished. There is no time interval between the extinction of the flame and its reignition during which an explosive mixture could form within the body of the lamp, hence internal explosions are impossible.

The lamp shown in Fig. 2 was subjected to the effect of a dynamite shot, lifting bottom, in one of the mines of the Wyoming region. This was a most severe test, the lamp being placed within 30 ft. of the shot. Several open acetylene lamps were placed beside it, and other open acetylene lamps were with the observers at a point 60 ft. up the gangway from the safety lamp. All these lamps except that fitted with the reigniter were instantly, and of course permanently, extinguished.

The acetylene safety lamp cannot be extinguished by shocks or jars as in the case of the benzine or kerosene burning lamp, and the automatic reigniter which we have provided eliminates the question of extinction from concussion. We believe that the use of this lamp will effect increased efficiency in the operation of safety-lamp sections underground.

E. M. Chance.—What candlepower has this acetylene lamp?

T. M. Chance.—The 5-hr. lamp, with the flames rather high has a candlepower of 3.0, and in the 12-hr. lamp we normally get 3 to 4 candlepower.

S. A. Taylor, Pittsburgh, Pa.—What is the price of this compared with the other?

T. M. Chance.—That is a commercial question.

S. A. Taylor.—It is commercial, but still I think some of these men would like to know.

T. M. Chance.—I am speaking as an engineer, and not as a manufacturer, but of course I am interested in the matter of price and I believe the manufacturers will be able to put these lamps on the market to sell at about $3 to $3.50.

George Rice, Washington, D. C.—What is the method of relighting after the stored heat is dissipated?

T. M. Chance.—There is none at all, and I think it would be a fatal objection if we had such a thing. If the lamp does not generate properly, and due to that is extinguished, I think the miner should not be allowed to tamper with it. If the lamp is charged with carbide and water and fitted with a properly designed feeding device, it must continue to burn unless extinguished by concussion, and that is taken care of with the automatic reigniter. When the lamp is upset, the flame commences to burn in the gauzes (due to insufficient oxygen supply) but reestablishes itself at the burner when the lamp is righted.

George S. Rice— Don’t you find that with an explosive mixture of acetylene gas and air, the flame will pass through the gauze, whereas the flame of a methane mixture will not?

T. M. Chance.—I presume you are alluding to the Belgian experiments. These experiments showed that a lamp generates acetylene with the flame extinguished, and that this acetylene may be fired by a burning lamp, provided you have these conditions: A lamp hanging perfectly motionless, in an absolutely quiet atmosphere, with a perfectly explosive mixture of acetylene and air. I believe M. Lemaire, who was in charge of this work, made the statement that while this was true, it was not fair to the lamp, because in a mine the lamps are not used hanging in a tightly closed box. The best proof of this can be shown by placing the two lamps together, one with the flame burning and the other generating acetylene with the flames extinguished. It is readily seen by placing the burning lamp side by side with the lamp generating acetylene that no passage of the flame takes place to the exterior acetylene.

George S. Rice—Then your system to meet that particular condition would be to have underground relighting stations or stations where the miner could change his unlighted for a lighted lamp?

T. M. Chance—Just as in any colliery where a large number of safety lamps are used and where the percentage of outage is large. I understand that in England at one colliery test an average of 2.5 per cent, of the lamps used underground were out per shift. As I said before, the only thing that can extinguish this lamp is failure of the generator to generate acetylene. I do not think a lamp can be produced that will be absolutely fool-proof. You cannot build an electric lamp in which the wiring cannot be short-circuited or the battery cannot fail.

D. B. Reger, Morgantown, W. Va.—Have you ever tried any different mechanical arrangement of the safety lamp so that you can get different illumination in the roof of the mine and the bottom of the mine? My experience was that with the safety lamp I could not see the roof at the top nor see the bottom of the mine.

T. M. Chance.—-You can see the roof with an acetylene lamp much more clearly than with the other types; the roof looks gray instead of black. I believe there might be some advantage in producing a lamp in which some of the light was reflected from the top. That is merely a matter of optics.

R. V. Norris.—Is it a question of utility?

T. M. Chance.—And optics to get a satisfactory lamp.

R. V. Norris.—Can that lamp be put out?

T. M. Chance.—Yes, it has a valve for that purpose.

R. V. Norris.—How?

T. M. Chance.—By turning the valve.

R. V. Norris.—Are you now generating acetylene under pressure?

T. M. Chance.—No, the water is cut off and the gas valve is shut and what little generation is still going on is bypassed to the atmosphere.

George S. Rice.—This appears to be an interesting and perhaps a very valuable discovery. Do you think there is any material danger, if two men are provided with a lamp, and one lamp has gone out, and the men are carrying the lamps in juxtaposition, of gas generated from the first lamp being ignited in the second lamp, the flame flashing through the gauze?

T. M. Chance.—Absolutely none, because if the men are walking together they are moving in the air.

As to this other question of the firing of one lamp from another, it is simply a matter of refrigeration, i.e., of having sufficient screen capacity. This can be seen by lighting the acetylene generated upon the top of the gauze. The acetylene remains ignited and burns on the exterior of the gauze like a Bunsen burner, but the flame does not pass through the gauze into the body of the lamp. The gauze must be in a red-hot condition before it will pass the acetylene flame. I would like to emphasize the fact that acetylene has no peculiar characteristics of importance in this connection, other than its low kindling point.

E. M. Chance.—These lamps generate about 5 or 6 liters of acetylene an hour, and the volume of explosive mixture is so insignificant that it is almost impossible to obtain an aura about the lamp, an explosive aura, when there is the minimum movement of air. The acetylene is generated at a higher temperature than the air, and tends to rise and move away from the lamp all the time.

E. T. Lednum, Chicago, III.—You spoke of an experiment with an explosion of dynamite, or high explosive, as extinguishing that light. Have you ever tried it with black powder?

T. M. Chance.—The small 5-hr. lamp with a single-jet burner was tried on two different occasions and successfully withstood the effect of a black powder shot at both places.

E. T. Lednum—The black powder shot is of longer duration.

T. M. Chance.—That may be true, but it does not have the same reversal of pressure that accompanies a dynamite explosion, and it has nothing like the effect on an acetylene lamp.

R. Dawson Hall, New York, N. Y.—What are the weights of the various lamps?

T. M. Chance.—The 12-hr. lamp weighs 5 lb. 13 oz., charged with carbide and water; small lamp 3 lb. 13 oz.; Wolf benzine lamp 3 lb. 8 oz.; Ackroyd and Beat 3 lb. 8 oz.; small Davy lamp 2 lb. 4 oz.; 12-hr. acetylene lamp is massively built, and we think the generator can be considerably lightened.

R. Dawson Hall.—What possibilities are there in the acetylene lamp of breaking the glass of the lamp; that seems to be the weakest point in it; when you lean it over on one side you are liable to break the glass.

T. M. Chance.—There is this difference: When the oil lamp is upset, if the light does not go out the flame burns against the glass and is sure to break it, whereas with the acetylene lamp the flame almost immediately commences to burn up in the gauze and thus saves the glass. The Belgian Commission made a number of tests of glass breakage with acetylene lamps, and did not find it a serious or valid objection to the lamp.

R. Dawson Hall.—Have you determined as to the “pick-up” power of the lamps, the amount of fire-damp you can pick up with the lamps?

T. M. Chance.—That is simply a question of heat value; if you have a hot flame you can pick up the gas. The European experimenters have found no difficulty in that direction.

Hugh Archbold, Scranton, Pa.—Some time ago I stuffed gauze on the ordinary acetylene cap lamp and tested out in competition with the Davy, to find out if the acetylene picked up as well. With the long flame that the acetylene lamp gave, I found I was able to pick up a cap where I could not do it with the Davy.

T. M. Chance.—About 1840 the Muessler lamp was introduced, and since that time the vast majority of safety lamps used abroad, and in later years in this country, have been lamps equipped with a glass shield over the flame, and the experience of almost 80 years has shown that the danger due to glass breakage is a negligible quantity. When a glass breaks in a well-designed safety lamp the upper portion of the lamp structure holds it in position, and as it is placed under compression when the lamp is screwed together it stays in position in the lamp body.

The miner’s electric cap lamp is a very different proposition; if the miner does not catch his battery against the caps in an entry he is exceedingly likely to strike the roof with his head and break the lamp glass. The strength of the average cap lamp protective glass and electric bulb is very different from that of the cylindrical safety lamp glass held tightly in compression.

G. H. Stickney, Cleveland, O.—Referring to the lamp on exhibition, I would like to inquire about the possibility of gas ignition if the glass is accidentally broken. This point was very strongly emphasized by the Bureau of Mines in connection with the design of electric mine lamps.

No doubt the members of the Institute have an immediate interest in the particular apparatus described here. As an outsider, however, I am disappointed that the discussion has not taken up the general subject of mine lighting suggested by the paper. I sincerely believe that the provision of better illumination in mines will, in the long run, prove of vastly more importance. In the past few years one industry after another, has emerged, so to speak, from the gloom, and whereas formerly it was considered practicable to get along with almost no light at all, higher and higher standards have been demanded. These have resulted in remarkable gains in safety, efficiency; and economy. While mining experts today seem to feel they are getting along fairly well with the low intensity employed, I believe before long it will be found not only profitable, but actually necessary, to raise the standards of illumination far above any which you now conceive.