Many attempts have been made by inventors to produce a reliable portable electric lamp for use in mines, which would be a perfect safety-lamp, and at the same time give a better light than that yielded by the ordinary oil safety-lamp, but without success, until the introduction of the Sussmann lamp.

An electric lamp is necessarily composed of two distinct parts — (1) The battery supplying the necessary current, and (2) the lamp itself.

With the latter there has not been much difficulty an incandescent lamp or bulb enclosed in a suitable lantern or cage being all that is necessary, provided of course that the carbon-filament has an average life.

Primary batteries were at first tried, many of them of original and ingenious design, but all that have come under the writer's observation have failed for various reasons, chiefly, because under the rough usage experienced in mines it was impossible to keep them tight, and the corrosive action of the liquids employed quickly destroyed the fittings and connections of the lamps, and the batteries themselves. The daily renewal of the elements was also a source of trouble.

The battery of the Sussmann electric lamp has solved the difficulty. It is practically a dry battery, there is neither leakage nor fumes, and it has successfully stood daily working-tests over a period of three years.

A small number of Sussmann lamps were introduced at Murton colliery in September, 1897. The result being so satisfactory as to warrant the trial of the lamp on a larger and more practical scale, 500 lamps were put into regular work in October, 1897; 100 were added in April, 1898; and 400 in September and October, 1899; making 1,000 lamps now in daily and successful operation.

At first, the Sussmann lamp was objected to by the workmen on account of its weight (4 pounds), which is heavier than the ordinary safety-lamp, and their reluctance to use anything new ; next, it was thought risky to depend upon the lamp, as it did not indicate the presence of gas. These objections were, however, by degrees removed, and the difficulties afterwards encountered were more of a practical character, particularly the extinction of the incandescent lamp or bulb, and failures of connexions and of batteries, the last being the most troublesome.

The number of failures of the ordinary oil safety-lamp, or extinctions from all causes, failure of oil or wick, being knocked over, falling down, etc., is much larger than might be expected; and it was found, on a careful record being kept, to be 2.11 per cent, of the number of lamps in use.

Even at the first, the failures of the electric lamp were not very excessive, being from all causes only 3 per cent.

At the present time, so thoroughly have all the defects and weak points been remedied, and the lamp improved, that the failures are only 0.01 per cent.: in fact it is a most unusual thing for a lamp to go out, except when crushed or broken by actual violence.

The writer feels fully justified in saying that the Sussmam lamp possesses the following excellent qualities :— (1) It is absolutely safe in an explosive atmosphere ; (2) it is more reliable than an oil safety-lamp; (3) it gives double the light of an oil safety-lamp; (4) it is as portable and as easily carried as an oil safety-lamp; (5) it keeps perfectly cool in the warmest working places ; (6) it does not go out it upset or turned upside down ; (1) it is more easily cleaned; (2) it dispenses with the staff of examiners required for the oil-lamp; and (9) in cases of accident, and workmen being isolated by falls or other causes, a few lamps will provide light for many hours in succession, say 9 hours per lamp, 5 lamps for 45 hours, 10 lamps for 90 hours, and so on.

Before adopting the lamp, the writer made many experiments to satisfy himself that ignition would not take place if the bulb were broken in an explosive mixture. This was done in mixtures of coal-gas and mine-gas, with incandescent lamps varying from 1 to 16 candle power, and currents varying from 4 to 110 volts. The result was invariably the same; and out of many experiments there was no ignition, while faulty oil safety-lamps, under the same circumstances, at once exploded the inflammable mixture.

The Sussmann Lamp. — Each lamp consists of two parts :— (1) The cage or lamp-top, containing the incandescent bulb or lamp (completely protected, and fitted with a switch for lighting or extinguishing the lamp at will) which is securely locked to (2) the battery-case with a leaden plug. The lamp is made in two patterns : Fig. 1, with an ordinary or fixed bulb, and Fig. 2, with a top (patented by the writer) containing a removable bulb, so that in the event of a bull) failing in the mine, the deputy or other official can replace it by a new one, in a couple of minutes.

The Sussmann Battery. — The Sussmann secondary battery is of the Faure or pasted type, and consists of 2 rectangular ebonite-cells, each cell containing 3 elements — 1 positive and 2 negative. These elements are made of cast-lead plates or grids, with a stout framework tapering inwards, and are pasted or filled with oxide of lead, incorporated with a special binding material, and made into a paste with dilute sulphuric acid or sulphate of ammonia — the mass being pressed into the leaden grids and allowed to set and dry for 4 days.

When dry, the plates are placed in a bath containing dilute sulphuric acid, and are formed or converted, the positive into peroxide of lead, and the negative into spongy metallic lead, by means of an electric current. After formation, the plates are placed in the ebonite-cells, connected by leaden strips and filled with the electrolyte. The electrolyte used in the Sussmann battery is semi-solid, the liquid-space being filled with a highly porous and absorbent compound, made conductive by saturation with dilute sulphuric acid.

The complete battery weighs 3¼ pounds, and has an electromotive force of 2 volts per cell, with a capacity of 5½ ampere-hours, which maintains the incandescent bulb for 8 to 10 hours with one charge.

All batteries, required for renewals, are made at Murton colliery, in the lamp-shop, which is completely equipped for that purpose.

Method of Charging Sussmann Batteries. — The batteries, having been removed from the iron cases, are placed on a suitable bench and connected in series, namely, the positive pole of one battery to the negative pole of the next battery, and so on, until the circuit is completed the outer positive pole is then connected through an adjustable resistance-board and an ammeter, to the negative main wire from the dynamo, and the outer negative pole is connected to the positive wire from the dynamo.*

The number of batteries so connected in each circuit depends upon the voltage of the dynamo used for supplying the charging-current. There are 2 cells in each battery, so that in arranging the circuits, 5 volts should be allowed for each battery, and the maximum number of batteries in series connected to a 110 volts circuit. should be 20, thus leaving a margin of 10 volts.

When the batteries are connected as above described, the current is switched on, and the resistance adjusted until the ammeter registers 0.65 ampere; they can even be charged up to 0.8 ampere, but this point should never be exceeded. Each battery has a capacity of 5½ ampere-hours, so that at the charging rate of 0.65 ampere it would he necessary to leave them connected for 13 hours, or for 12 hours at 0.7 ampere ; the lower rate being preferable.

When the batteries have received this charge, they are disconnected and replaced in the iron cases, the connexion-plugs from the lamps placed in the holes of the batteries, the lid closed and locked, and the lamps sent out for use.

Dynamo. — The dynamo for supplying the current for charging the lamps is driven by a separate engine. It is capable of delivering 75 amperes at 110 volts, at which pressure the current enters the resistance-board, referred to when describing the method of charging the batteries. The dynamo also supplies current to the 16 candle-power lamps in use in the lamp-rooms.

Results of Working. — The Sussmann electric lamp costs 18s. The cost of working the lamps over a period of several months, including all charges except interest on capital and the cost of running the dynamo, has been as follows —

Pence.
All labour, at basis rates, including superintendence, cleaning, making ready, maintenance, etc.	2.19
Material for renewing batteries, repairing and maintaining the lamps in every part, and lamp-glasses	1.00
Incandescent lamps or bulbs	0.60
Total	3.79
With wages at 52 per cent, above basis rates the cost is increased by	1.03
Total	4.82

The life of the battery, up to the present time, averages 10 months, but certain improvements have recently been made whereby it is expected to reach 12 months.

The lamps have now been in use for 3 years, and there has never been the slightest accident that can be attributed to their use. At first, it was supposed, as the lamp did not indicate the presence of gas, that men might work unconsciously in an explosive or irrespirable atmosphere; but such an event has never happened. The precautions adopted for safety are the same as before the introduction of the electric lamp. The deputies (who all carry oil safety-lamps) visit and examine the working-places before the commencement of and during the shift, and if gas be detected the men are withdrawn at once, precisely as if they were using oil safety-lamps, which, in the presence of an explosive mixture, are a source of danger while the electric lamp is absolutely safe. The putters use oil safety-lamps, which can be used by the hewers to examine their working-places, if they suspect the presence of gas.

A careless man has been found working in a place which has suddenly become "foul," with the gauze of an oil safety-lamp red-hot and in a very dangerous condition to the individuals working in the place, and to all the men employed in the mine ; but with an electric lamp this danger cannot happen. Then again, an accident to an oil safety-lamp in a "foul" place, a blow from a pick, or a fall of stone or coal, might cause a disaster, but this risk is impossible with the electric lamp, as the breakage of the bulb is followed by the instantaneous extinction of the light.

The object of introducing the electric safety lamp at Murton collieries was entirely in the interest of increased safety, which was secured by (1) the increased light, enabling the workman to make a better examination of his surroundings ; (2) the use of a source of light, which minimizes and indeed absolutely removes the risk of igniting explosive gas, an element of danger which is never absent, either from accident or mistake, in the use of an oil safety-lamp. The managers of fiery mines will fully realize that they are entirely relieved of an enormous weight of responsibility and anxiety by the use of the Sussmann lamp.

In conclusion, the writer may add that he has made the foregoing paper of as practical a character as possible, and confined his remarks strictly to his personal experience gained in the use of the Sussmann lamp.

* The charging-current must be direct, and not alternating.

Mr. Sydney F. Walker (London) suggested that the secondary batteries used with the Sussmann lamp should be charged singly, and not in series. rfhere is always a danger when secondary cells are charged in series, that one or more of them may not be taking its proper current, and there will be nothing to show this, except the fact that the lamp will not last out its proper time. The best arrangement, in his opinion, would be, where an electric light or power service exists at the colliery, to put in a small continuous-current rotary transformer, arranged to deliver current at about 6 volts, to a pair of bars on which would be fixed flexible cords with plugs attached. If the cords are of different colours, say + red and - green, it would be a very simple matter to make connection with the batteries, and to keep these cords clear of each other. Attached to one of the bars, also, should be a small galvanometer, for each pair of cords, so that the attendant could see at a glance whether any cell was not taking its charge. Simple boards, lead-covered, might be arranged with recesses for the cells, so that the work involved in setting any individual cell to charge would be very trifling. Where three-phase plant is installed at a colliery, the same plan might be adopted, the transformer converting the current into a 6 volts continuous current at one operation.

He was pleased to know that his estimate of the running cost, given in his paper, which was recently read before the Institution of Electrical Engineers, was practically confirmed by Mr. Wood's figures. His estimate was higher than Mr. Wood's figures, but it was on the supposition that battery-renewals had to be purchased complete. He ventured to think that if Mr. Wood and others, who are using Sussmann lamps, would adopt his suggestion for charging the cells, the cost for attendance would be materially reduced.

Mr. Austin Kirkup said that the Sussmann electric miners' lamp had been used at the Newbottle collieries for some months. The immediate object in giving these lamps a trial, was to obtain a better light at the working-face, so as to enable the miners to clean their coals more effectively than with oil safety-lamps. A better light was obtained, but the percentage of battery failures was much greater than appears to be the case at Murton colliery. An extraordinary number of batteries were cracked and rendered useless, by knocks which the lamps received in the pit, and this was attributed to the very light outer casing, containing the batteries. In order to reduce the weight of the lamp to 4 pounds, the makers have enclosed the battery in a very light and easily bruised iron casing, with the result that a by no means violent blow is required to damage the battery enclosed therein.

In regard to the safety of the workmen, when using this lamp in noxious gases, he could only give a qualified assent. Mr. Wood had used the Sussmann lamp for three years, and he stated that men have never been found working "unconsciously in an explosive or irrespirable atmosphere." He had only used the lamps for six months, and yet during that time, he came across two cases of men, who were working unconsciously in an atmosphere which was unfit to breathe, owing to the presence of carbon dioxide. This occurred, in spite of the fact that the deputy had visited the place a short time before, and found it well ventilated. Fortunately, in both the cases above cited, the men were young and strong persons, otherwise they would have been overcome by the irrespirable gas. He wished to enforce the point that in workings which are liable to sudden inrushes of carbon dioxide (a very small percentage of which mixed with air is dangerous to life) the Sussmann lamp is not to be desired, In the pit to which he had referred, both fire-damp and carbon dioxide are found, and although in an explosive mixture of fire-damp and air, so long as it is not poisonous, the Sussmann lamp is to be preferred to an oil safety-lamp, yet, in the other case of a mixture of carbon dioxide and air, the Sussmann lamp is a positive danger, and is to be avoided accordingly.

In conclusion, he might mention an incident in the practical working of the lamp, where a leak-age of current had occurred (due, no doubt, to defective insulation) in the lid, which surmounts the battery and forms the base of the lamp. When contact was formed between this lid and the switch spindle, a spark was produced outside the lamp. This is not desirable in a fiery pit. He did not know whether other instances of this sort had occurred, but he mentioned it to show that every care must be used to ensure complete insulation of the lamp. The lamps were under the constant charge of one of the Sussmann Lamp Company's electrical engineers, during the whole of trial period of these lamps.

Mr. Geo. Ed. Smith (Nottingham) wrote that the members were indebted to Mr. Wood for writing this paper, containing the result of 3 years practical experience with a new and absolutely safe lamp. He should like to ask Mr. Wood how he ascertained the condition of his secondary battery and, if fully charged, since the electrolite is practically dry and no fumes, that is no gas is given off, as the condition of the electrolite is generally used as an index to the good or bad condition of the cell; whether he considered a life of 10 months for the battery satisfactory; and whether at the end of this period both negative and positive plates required renewal. Did 10 or 12 months life mean that the lamps are charged and discharged once every 24 hours for say 300 times, as he believed that the life of a battery was greatly dependent on the number of charges and discharges, rather than upon the number of months it was in use.

The President (Mr. J. G. Weeks) proposed a vote of thanks to Mr. W. O. Wood for his interesting paper.

Mr. T. E. Forster seconded the resolution, which was cordially approved.