The conditions causing the burning, all or in part, of nitro-explosives instead of their detonation, are poor quality of the explosive, improper tamping, the use of detonators of insufficient strength of or defective fuses, and the actual burning of a quantity of the explosive by a fire carelessly started.

Haldane claims that nitrous fumes, NO2, are even more poisonous than those of H2S and says that no gas met in mines is so treacherous in its effects. These fumes act as an irritant to the eyes, nose, and throat not dissimilar to that of hydrogen sulphide and sulphur dioxide, but whereas the after-effect of recovery from the last-named gas is a temporary catarrh, with nitrous fumes there is great danger of intensely acute bronchitis, which is often fatal. While temporary irritation and apparent recovery may be experienced at the time of exposure, these are frequently followed by the development of bronchitis in a few hours and this is frequently fatal in 2 da. Mice forced to breath air containing but .05% of these fumes for 1 hr., and which apparently recovered, died within 24 hr. of bronchitis.

Nitrous fumes are easily detected by their smell, even when greatly diluted, and care should be taken in returning to the face if this smell is at all noticeable. Minute traces of the gas may be detected by exposing in the suspected air a paper soaked in a solution of starch and potassium iodide; if any nitric oxide is present, the starch is at once turned blue by the iodine set free.

EFFECT OF HEAT AND HUMIDITY ON MINE WORKERS

The mean annual underground temperature of the mines of the United States is probably about 10° more than that of the surface, and is between 60° and 65° F. The causes making for this increase in temperature are the heat given off by men and animals, by the burning of lamps, by the oxidation of animal and vegetable substances (as the decay of timber), by the slow oxidation of the coal, by gob fires whether active or smoldering, by the detonation of explosives, and by the interior heat of the earth. In deep mines, the effect of increasing heat with increasing depth is of prime importance in raising underground temperatures. Below the level of no annual variation which, in temperate climates is some 60 ft. below the surface, the temperature increases at a rate of from 1° F. in 100 ft. to 1° F. in 60 ft., or about 1° F. for each 80 ft. of descent. A mine 1,000 ft. deep in a region as western Pennsylvania and Ohio, where the mean annual temperature is about 55°, may reasonably be expected to have = 67°, about, due to the interior heat of the earth alone. To this must be added an always uncertain amount, perhaps as much as 2° to 3°, for the heat arising from the other causes named.

an average temperature of 55°+ (1,000—60)

80

Whether the temperature of the ventilating current will be greater or less than the temperature established by the preceding conditions depends on its initial temperature and its velocity. Radiation from the side walls is constant but slow and rapid currents of air will not absorb as much heat as those moving slowly; consequently, at the face or in any tight place the temperature is much, often 50 or 100, greater than on the entries where the air is circulating freely. Haas found that in a certain mine entry 4,000 ft. long, over 30,000 B. T. U. a min. were radiated from the sides, which is equivalent to the heat derived from burning more than 1 T. of coal a day. In regard to the initial temperature of the air, Scholz found at certain mines in the Middle West that during summer, when the temperature outside averages 85° F. for 24 hr., with a maximum of 95° to 100°, the mine temperatures fluctuated between 70° and 78°; and that during winter, with a temperature of 40° to 50° outside, the mine temperatures ranged from 60° to 67°, the exact temperature necessarily depending somewhat on the extent of the mine. As the average annual temperature of the region in question cannot be far from 55°, it would appear that at all times (even in winter) the temperature of the mine is considerably above the annual for the place.

As long as the mine air is dry, or relatively so, men can work in temperatures as high as 90° and even 100° without much discomfort or impairment of health, as the perspiration is rapidly absorbed by the air-currents. But it has been shown that, regardless of the outside temperature and humidity, the return air is usually saturated to the extent of 90% or more, except in the arid regions of the West, where the humidity may fall to 85%. Haldane states that in still and moist air it is hardly possible for men to do continuous hard work at temperatures of 80° to 85° even when stripped to the waist. At temperatures

above 90°, by the wet bulb, it is only possible to work for short periods, and it becomes increasingly difficult to remain in the place even without working. Haldane found that at a temperature of 93° in still and saturated air and doing practically no work, his temperature rose 5o in 2 hr. and was still rising rapidly when he found it necessary to go out.

SAFETY AND OTHER LAMPS

PRINCIPLE AND ORIGIN OF SAFETY LAMPS

Description. In a safety lamp, the flame of the burning illuminant is isolated from direct contact with the mine air by a wire gauze, or a glass and gauze cylinder, which is closed at the top where it is covered by a hood to which is attached a ring or hook for carrying. As a further means of isolating the flame, there may be two or more gauzes with an air space between each, and in practically all lamps the outer gauze is surrounded by a shield, called a bonnet, which is provided with perforations or slots. The various parts of the lamp are securely held together by the necessary standards and screw, soldered, or riveted joints.

Dates of Discovery. The principle of isolating the flame of the lamp was evolved by Dr. William R. Clanny in the spring of 1813, although his, the first safety lamp, did not receive its final and successful trial until Oct. 16, 1815. The principle of the bonnet was demonstrated on Nov. 28, 1815, by George Stephenson; and on Dec. 15 of the same year, Sir Humphrey Davy announced the use of the wire gauze.

Principles of the Safety Lamp.-Although the last to be made public, the principle discovered by Davy is the first in importance. This principle is that, while a wire gauze of fine mesh entirely surrounding the flame will permit the free entrance of air within the lamp, yet in its outward passage through the gauze the burning gas is broken up into a series of fine jets and is so reduced in temperature by the cool metal that its flame is extinguished and, hence, cannot ignite firedamp mixtures outside the lamp.

In Stephenson's lamp, the burning gas was extinguished not by a cool metal gauze, but by bringing it in contact with the inert products of combustion that were held in the upper part of the lamp between the bonnet and the gauze. While, in modern lamps the bonnet plays in a greater or less degree the part for which it was originally intended, its chief use is to prevent the direct impact against the gauze of air-currents of high velocity which might extinguish the lamp or, what is more dangerous, might force the flame against or through the gauze and thus cause an explosion. When the blanketing effect of the original bonnet is desired, it is now generally accomplished through the use of double or triple gauzes as in the Marsaut lamp.

Safety lamps are not absolutely safe in the sense that they may be burned indefinitely in explosive mixtures of gas and air. In comparison with the unprotected candles that they replaced or with modern open lights, they are relatively safe in that the warning of the presence of a dangerous amount of gas afforded by its burning within the lamp, gives the miner time to withdraw before an explosion takes place.

Early Classification of Safety Lamps.-Safety lamps were formerly divided into two general classes, those designed for testing for gas and those intended for working lamps, the construction of the former being such that they were the more sensitive to gas. This distinction in usage and construction is now rarely made, and at any particular mine the same kind of lamp is commonly used by fireboss and miner alike. The reason for this is that none but special lamps in the hands of skilled observers can detect the less than 1% of gas that is dangerous in the presence of explosive coal dust. Such being the case, there is nothing to be gained in providing a fireboss with a dangerous lamp (all sensitive lamps are unsafe) to detect 2.5% of gas when a safe lamp will detect, say, 3%; as these proportions of gas are equally dangerous when coal dust is present and equally harmless when it is not.

Approved Safety Lamps.-An approved safety lamp possesses those features that a mining department or legislature declares essential in lamps to be used within its jurisdiction. The features considered essential vary, but both here and in Europe, to be approved, a lamp must have a bonnet. The Davy lamp, not being safe with or without a bonnet, is not permitted in Europe, but is allowed in a few American states for gas testing, although the number of states permitting it is decreasing.

SAFETY-LAMP CONSTRUCTION

Specifications.-Mr. J. W. Paul sums up the structural requirements of safety lamps as follows:

1. The framework should be rigid and well made so that it will not get out of shape when roughly handled;

2. If the lamp has a glass chimney, the upright rods (standards) should be of such number and so spaced that a straightedge, or ruler, placed against any two adjacent rods will not touch the glass;

3. If a lamp has no bonnet, the gauze should be protected with rods in the same manner as the chimney, as indicated in 2;

4. The lock should be such as will require, when locked, a special device for unlocking;

5. The glass chimney should have a smooth and even wall throughout, should be of the best quality, and should have its ends ground truly parallel and at right angles to the axis of the chimney. The chimney should bear the trade-mark of the manufacturer;

6. When the lamp is assembled there should be no openings between the outside and the interior of the lamp except those in the gauze or other heatabsorbing device, such as a perforated plate or cylinder in which the size of the perforations corresponds with that of the gauze openings;

7. The handle of the lamp should be either an open ring or a hook, strongly made and not easily bent in the hand;

8. The construction of the lamp should be such that its parts are made in standard uniform sizes and fit so intimately that should any part be omitted in assembling its absence would be easily detected by the most casual inspection;

9. There should be an expansion ring or equivalent device used with the glass chimney so that the chimney when heated can expand without breaking any part of the lamp;

10. In the selection of a safety lamp, carefully examine each of the disassembled parts to ascertain defects or improper construction; if any such is discovered, the entire lamp should be rejected.

Design of Safety Lamps.-As pointed out by Hughes, Marsaut and others have shown that a certain relation should exist between the volume contained within a lamp and the gauze surface open for the escape of the products of combustion resulting from an internal explosion, as experiments have proved that the ignitions of explosive mixtures outside the lamp by explosions within it become less frequent as the open surface of the gauze is enlarged.

Marsaut also proved that: (1) A lamp of small diameter (such as a Davy) does not readily pass an explosion, as the volume of gas that can be exploded is insignificant. (2) A lamp without a glass is more secure against the effects of internal explosions than a lamp with a glass cylinder, as the latter confines the gases at the time of an explosion and acts like a cannon; it is, therefore, advisable to reduce both the height and the diameter of the glass. (3) A wire gauze of conical shape is more secure against the transmission of internal explosions than is one of cylindrical shape and of the same capacity. (4) Gases resulting from combustion play a certain part in preventing external explosions and it might, therefore, not be advisable to guide them by a chimney. (5) A descending current of feed-air prevents the filling up of glass lamps with an explosive mixture, and occasions the formation of an inexplosive and elastic cushion at the bottom of the lamp.

Materials of Construction.With the exception of the gauze and glass, the various parts of safety lamps are made of brass or, where lightness is required, of aluminum or magnalium. Where iron enters into the construction, it is usually in the standards and hood.

Safety-Lamp Gauzes.-The main gauze of safety lamps is of 28 mesh; that is, there are 28 openings in 1 lin. in. or 784 openings in 1 sq. in. If made of No. 28 (B. W. G.) wire .014 in. in diameter as is usual, 1 sq. in. of the gauze will be about two-thirds (.6151 sq. in.) metal and one-third (.3849 sq. in.) openings. As exceptions to the use of this standard gauze, those in the Marsaut and Chesneau lamps have 934 and 1,264 openings per sq. in., respectively.

Gauzes are commonly made of iron wire, although copper is sometimes used. The latter is rather more durable than iron as it does not rust or burn out so quickly, but it becomes hot and passes the flame sooner than iron as it has a higher specific heat.

The gauze cylinder must not exceed a certain size, which Davy fixed in his original lamp as 2 in. in diameter and 7 in. high (contents 22 cu. in.), otherwise the burning of the large volume of gas within it will heat the gauze, and par

ticularly the top, to a point where it will no longer cool the flame sufficiently to prevent its igniting gas outside the lamp. In modern lamps, the diameter of the gauze is about the same as that of the original Davy, but its height is less and varies from 4 to 5 in., as the lower part is replaced with glass. In lamps built on the Eloin principle, that is in those lamps that take air in through ports below the flame and are thence known as underfeed or underdraft lamps, as all the gauze is available for the discharge of the combustion products, it may be made much smaller than in a lamp of ordinary construction. The Ashworth-Hepplewhite-Gray lamp, Fig. 1, e, page 885, is an example of a lamp with a relatively small gauze.

As the top of the gauze receives the full effects of the flame, it is often reinforced by what is known as a gauze cap or smoke gauze. This consists of a cylinder of standard gauze closed at the top, which fits snugly over the main gauze for about one-third its length. The upper part of this cap is sometimes crimped or indented so that it may not be pushed too far down upon the main gauze as it is desirable to leave a small space between the tops of the two.

The gauze of the early lamps was always cylindrical, but in many modern lamps it is in the form of a truncated cone; a shape commonly followed where there is more than one gauze.

Safety Lamp Glasses. Although Clanny and Stephenson used glass in front of their original (1815) lamps to increase the light-giving power, the present form of safety lamp in which a glass cylinder entirely surrounds the flame and is surmounted by a cylinder of gauze is due to Dr. Clanny who appears to have combined ideas original with both Davy and Stephenson. In a general way, modern lamps may be said to be Davy lamps in which the lower por. tion of the gauze cylinder is replaced with one of glass; or to be Stephenson lamps, the perforated metal cylinder being replaced by one of gauze.

Glasses are commonly cylindrical, but in the Ashworth-Hepplewhite-Gray lamp they have the shape of an upward-tapering truncated cone. This form allows the upward diffusion of the light, at least in pary, and thus permits of a closer inspection of the roof without having recourse to the very dangerous practice of turning the lamp on one side.

Multiple Gauzes.-Some safety lamps are made with two or even three gauzes, one within the other, with a small air space between; and lamps so made are known as multiple-gauze lamps. The inner gauze is always conical but the outer gauze may be cylindrical or conical with a little more slope than the inner one so that there may be more air space between the gauzes at the top than at the bottom. The intention of multiple gauzes is to interpose one or more curtains or screens of inert gases between the flame of any gas burning in the lamp and the outside air. These screens are formed by the retention of the products of combustion in the spaces between the several gauzes. The multiple gauze is the modern development of the original Stephenson principle of preventing the outward passage of the flame by smothering it in inert gases, and adds greatly to the safety of the lamp.

The effect of these gas screens is to impede the free upward and outward passage of the products of combustion simultaneously reducing the amount of oxygen admitted to the flame and the amount of oil burned in a given time. In other words, they reduce the draft and thus increase the tendency of the lamp to smoke and diminish the illuminating power. The reduction in illuminating power increases with the number of gauzes. Thus, the Marsaut lamp, Fig. 1, d, page 885, with three gauzes has an illuminating power 20 to 25% less than the same lamp with two gauzes. In lamps admitting air on the Eloin principle and which, in consequence, have a strong natural draft, the reduction in illuminating power through the use of multiple gauzes is considerably less than in lamps drafted in the ordinary way. With multiple gauzes, the gauze cap (smoke gauze) is rarely used.

Safety-Lamp Bonnets.-A bonnet consists of a metal cylinder entirely surrounding the gauze of the safety lamp, and is intended to prevent the direct impact of air-currents of high velocity against the gauze, as explained under Principles of the Safety Lamp. The surface of the bonnet is usually smooth, but in the Wolfe lamp, Fig. 1, f, page 885, it is corrugated. The bonnet is perforated or slotted with a varying number of holes arranged in various ways and which are designed to permit access of air to and egress of combustion products from the lamp. In some bonnets, the slots are indented on one side or arranged on the corrugations (Wolfe lamp) so that the air enters tangentially and not directly against the gauze. In the early Davy lamp, the screening effect of the bonnet was secured, but only in part, by the use of a semicircular shield that could be slipped in front of the flame when moving against the air.

The fewer the perforations or slots, the greater the blanketing effect of the bonnet and the more nearly it approaches a series of gauzes in its influence on the circulation of air within the lamp and on its light-giving power. Lamps with tight-fitting bonnets are easily extinguished when exposed in high percentages of gas, the flame being smothered by the large volume of combustion products held back by the imperfect circulation.

In the Ashworth-Hepplewhite-Gray lamp, a double bonnet is used, and double- and triple-gauze lamps are always bonneted for general use and commonly so when employed for gas testing.

Circulation of Air in Safety Lamps.-Air is admitted to safety lamps in three

ways.

In the Davy lamp, Fig. 1, a, page 885, the air enters at the bottom of the gauze, which extends below the top of the wick tube, and the products of combustion pass upwards and out through the top of the gauze.

In underdraft lamps (Eloin principle) as in Fig. 1, e, page 885, the air enters below the flame through gauze-protected ports, and the products of combustion follow the same course as in the Davy lamp.

In the majority of lamps, Fig. 1, b, c, and d, page 885, the air enters at the base of the gauze above the glass and must pass downwards to the flame.

Lamps of the first two classes, in which the air follows what may be called the natural course (as in an ordinary chimney) are sensitive to small amounts of gas, are apt to flame readily, are adapted to gas testing but not to general use, and are unsafe in air-currents of any but very low velocity unless provided with bonnets or multiple gauzes. When so equipped, underfed lamps are excellent for general use, but are not so sensitive to gas as otherwise.

In the third class, the air in passing down to the lamp flame conflicts with the ascending products of combustion with the formation of eddy currents, which may cause the lamp to flicker and smoke, thus making it less sensitive to gas and decreasing its illuminating power. In the Mueseler lamp, Fig. 1, c, page 885, the flame is surmounted with a conical sheet-iron chimney, which increases the draft and causes the air to circulate in a natural course. Following the arrows, the air enters through the base of the gauze, passes down beside the chimney to the wick, and the products of combustion pass up the chimney and thence out through the upper part of the gauze (see Mueseler lamp). It should be noted that a bonnet or a series of multiple gauzes interferes with the rapidity but not with the direction of air circulation.

In order to detect thin layers of gas near the roof without the dangerous necessity of turning the lamp on one side, of waving it to and fro, or of brushing the top air down upon it with a cap, several special constructions are employed. In the Ashworth-Hepplewhite-Gray lamp, the standards are hollow and air can, when needed, be drawn down through them by closing the regular entrance ports at the base of the lamp. A device for the same purpose that may be attached to ordinary lamps consists of an L-shaped pipe about in. in diameter, the short arm of which is attached to a special port in the lamp below the flame while the long arm projects upwards into the gas. An improvement on the preceding is used by Mr. Joseph Smith, general superintendent of the Stag Cañon Fuel Co., at Dawson, N. Mex. The device consists of a small, doubleacting pump the discharge end of which may be directly connected to the base of any of the standard forms of safety lamps. By means of a number of 5-ft. lengths of 1-in. gas pipe which may be screwed together until their combined length is sufficient to reach the top of the highest falls and then attached to the suction end of the pump, samples of air from_otherwise inaccessible places may be drawn into and through the lamp. For the same purpose Sir William Garforth uses a rubber bulb with a strong metal nozzle. In the base of the safety lamp is a tube with a self-closing valve. When testing for gas, the bulb is placed in a cavity in the roof or other place where gas is suspected, and is filled with the firedamp by compression in the usual way. The gas is prevented from escaping by holding a finger over the nozzle and the lamp is taken to some safe place where the end of the bulb is inserted in the tube in the lamp, opening the valve in so doing, when the gas may be squeezed upon the flame.

Wick Tubes, Wicks, Etc.-The wick tube of a lamp may be round or flat. When flat, one side is commonly made with one or more grooves to reduce the friction when the wick is adjusted in height and to provide a space for the circulation of the air that the oil may ascend. The top of the tube should be set about in. above the base of the glass for, if set too low, the shadow cast on the ground by the body of the lamp is increased; and if set too high, the amount of light diffused upwards is decreased. In many lamps, in one side of the wick tube is a narrow slot in which the point of the picker is inserted to