Faraday report to Trinity House   15 February 1837

Professor Faraday’s Second Report, - being the Frist on the Bude Light, - dated, 15th February 1837.

To the Master, Deputy Master¹, and Elder Brethren of the Trinity Board.

My Lords and Gentlemen,

I have the honor to present a first report on the plan proposed by Mr. Goldsworthy Gurney for the production of an intense and convenient Light to be applied in the illumination of Light Houses². The proposed plan has been tested and is in progress of trial by an apparatus on a scale sufficient to prove it’s applicability in practice; and though much remains to be done before it can be supposed that it’s capabilities have been proved to the full extent; or even before a judgment can be formed as to the final condition and advantage of the plan; yet enough has, I think, been ascertained to justify this first report, and to enable the Board to come to a conclusion, whether the practical experimental examination which has been carried on thus far, shall or shall not proceed further.

Mr. Gurney’s plan consists in throwing Oxygen gas into the middle of a flame derived from the combustion of ordinary Oils upon Cotton Wicks, in such a manner that the luminosity of the flame shall be very greatly increased and yet the Wicks not be charred or injured more than in a common lamp. I will endeavour to take a brief review of the general plan of operation, and the results up to this time, so as to shew what has been already effected: without however describing minutely, arrangements which have been, and, from the improvements contemplated, are still subject to change.

The Oxygen gas has been obtained from two sources; Nitre, and the Native Oxide of Manganese. When Nitre is heated in a close vessel it yields much Oxygen mixed with some Nitrogen and Nitrous Compounds, and leaves an alkaline substance in the vessel used. The gas is obtained from this Salt very quickly; and tho’ not pure, is powerful as an agent in exalting the light. The alkaline residue is however a very active flux, and in the experiment made corroded the iron retort to such a degree, as to make a hole thro’ it, and render it at once useless. For this and other reasons founded on the relative price of Nitre and Oxide of Manganese, as compared with the quantity of Oxygen they can produce, and the facility and regularity of the operation by which these substances are respectively made to yield their gases, the latter has been thus far preferred.

The gas making apparatus.

To obtain Oxygen from Manganese the mineral merely requires to be heated to a fair full red heat in a close vessel. For this purpose retorts of Cast Iron have been constructed (which with all the other apparatus have been arranged under Mr. Gurney’s direction) and fixed in brick furnaces, so as to be subjected when needful to the necessary heat. The teaching of experience has caused these retorts to be changed in their form, two or three times; and still further alteration is contemplated when the present one is worn out, or perhaps earlier. Similar improvements have taken place in the setting, for some of which we are indebted to Mr. Winsor’s³ kindness, exerted at my request. The present retort is a Cylinder four feet, six inches long, five inches diameter inside, and half an inch in thickness. It has a feeder connected by a wide cock and pipe, and acting like a funnel, by which the Oxide of Manganese can be introduced; it has an aperture at the bottom near the front usually closed by a screw, by which the exhausted Manganese can be withdrawn; and it is also supplied with a sliding rod, passing through a tube and stuffing box, by means of which the Manganese within the retort can be moved, distributed, collected, or discharged at pleasure. The whole works well at present, but will perform better when the contemplated changes are made.

The gas passing from this retort, is conveyed by pipes first into a water vessel, where any steam which may be evolved from the Manganese may condense, and then into a gasometer to be received and retained for use.

This gasometer has been made upon a full scale. It is of Copper, is 57 inches high in the Bell, 69 inches in diameter, and will hold 130 cubical feet of gas. It is furnished with the necessary pipes and stop-cocks by which the Oxygen can be supplied at pleasure to the light or be shut off, and retained for future service.

The first class of results necessary to be observed relate to the use of the gas-producing apparatus, and the time employed. With a retort of the size described, the quantity of Manganese most advantageously introduced at once has been found to be about fourteen pounds. When the retort is fairly hot this quantity yields it’s oxygen in from thirty to forty minutes. On one day as many as eleven of these charges were made in succession, and tho’ the retort was not at the commencement of sufficient temperature, yet the time occupied was only Seven hours, whilst the quantity of gas produced was 96 cubical feet. As the consumption for the large Quintuple or Trinity Lamp, hereafter to be referred to, is about 4.6 cubical feet per hour, the quantity thus produced would have lasted nearly twenty-one hours. Thus even this apparatus is able to produce within a reasonable given time, the supply of oxygen needed for the longest night in the Year, by a lamp, which as far as I have as yet proceeded, surpasses the French lamp in light in the ratio of 13.2 to 10.

The iron retort has now been heated twenty different times, and on the whole looks well: but it would be unfair to judge from the present retort of the probable duration of another. Not having been set properly in the first instance, it bent in the middle, and when reset under Mr. Winsor’s directions, it could not be protected sufficiently from the partial action of the fire or sustained as it ought to be; and therefore is more liable to injury than another would be fixed in a proper manner. Still as I said it looks well; it has not been oxydised within, to any thing like the extent that I expected; and tho’ continued experiment only can decide upon the duration of these vessels, I have sanguine hopes that their decay will not be so rapid as to cause any objection to Mr. Gurney’s plan. It is in the setting and use of the retorts, as much as in any other part of the general plan, that gradual and great improvement may be expected.

With regard to the gasometer, it acts well, and can contain gas enough for more than 28 hours consumption. It is not liable to change or irregularity and need cause no fears for it’s use. Certain variations in the directions and attachments of the pipes will be required if the plan is carried into practice; and certain appendages to act as indicators, removers of extra water &c: &c:- but these will cause no variation of, or interference with, the principle of the plan.

The use of a furnace, and the production of oxygen gas is something very different to the common occupation of the present Light House Keeper. But I can see no difficulty in the apparatus being properly worked by a careful man of ordinary intelligence. Even now it comes within the powers of such an one; and when simplified by further experiment, will I think leave no excuse for failure to an attentive Keeper. One part of which I am rather more anxious than about the others is the setting of new retorts when an old one is worn out. It may however ultimately appear from experiment that this will not be frequently needed:- and then probably if two or three retorts are set at once, so that when one is injured another may be resorted to; it may be found most advantageous that fit men should be sent at convenient times to restore those that are injured.

As I think it my duty in this stage of a very important enquiry to notice all the probabilities which occur to my mind as bearing upon it, I will remark that the character of the light would not be quite so independent of the temptations which might arise in the mind of a careless, idle man, as the common light. It has occurred to me that such a man might at times be moved to mix air with the oxygen in the gasometer, instead of making the quantity required for the night - and I do not at present see, what check could be put over him (except those of a moral nature) which should prevent his doing so. Still I do not look upon the possibility, as one which ought to affect the character of the light, but think that if it should occur, it should rather be met in some other way, as for instance immediate discharge of the man, than by rejection of the lamp.

It will be necessary for me to mention that there is no risk, in the use of oxygen gas, of any of that class of accidents, such as explosion &c:- which sometimes occur with common combustible gases.

The Light or Lamps.

As I have before said the principle of Mr Gurney’s Light is to form an ordinary smoky flame from common oil, burning on a Cotton Wick in common air, and then throwing oxygen by a jet or jets into the middle of it, this at once converts the large, smoky flame, into a short and very brilliant one, the light being increased (as I find by experiment) for the same quantity of Oil above five times. In what Mr. Gurney has called the Bude Light a circular cotton is extended in one direction so as when lighted to produce a flattish flame about 1⅜ Inch in one direction, and half an inch in the other direction at the base. Three jets which rise up thro’ the middle of the oil are placed in a row at distances ascertained by experiment to be best in their effect; and when the gas cocks are opened throw oxygen into the focus of combustion. The Cotton is adjustable by a rack with great facility; the flame which without the oxygen is long unsteady and smoky, upon the introduction of the gas becomes very much shorter, clear of smoke, more steady, and intensely bright.

In the Trinity or Quintuple lamp, five of these Bude elements are arranged together, with a single cotton and jet in the middle; the whole offering a circular or rather sym[m]etric arrangement not exceeding four inches in it’s horizontal projection.

The Oil is laid on to the Cottons in the lamps on the principle of hydrostatic pressure in the manner suggested and applied by the Deputy Master, in regard to the French Lamp:- The oxygen is supplied by a pressure of about 3 inches of water from the gasometer to the jets, or rather to a space into which all the jets open. Each separate jet has a regulating cock, and when these are once adjusted, then one general cock serves to put on or shut off the supply of gas.

The regularity of the flame of this lamp is very great and highly satisfactory. It appears to change less even than a common Argand lamp, and considerably less than the French lamp. The reason is that the place of highest combustion is removed to a certain distance above the wick by the elevation of the oxygen jets within; and this is a most important part of the arrangement; for instead of the wick being highly heated, and rapidly charred, as happens when the arrangements are such as to throw the supporter of combustion forcibly and directly on to it; the Cotton and Oil are not heated in this lamp even so much as in a common Argand Lamp; the wick therefore does not become charred so soon as it otherwise would be, but remains for many hours in steady action, supplying an equal flame, and yet there is an abundant production of the vapour of Oil to burn at the place above, where it meets with the oxygen. The moderate supply of common air at the generating place of the flame at the outside of the wick, and the supply of oxygen at a higher point inside where the Light is to be evolved, is a happy association of circumstances for the production of a flame at once brilliant and regular.

When all is in order the flame is not above three inches high, and indeed, the effective part is not more than one inch in height, so that the Light is very advantageously compressed in a vertical direction.

For the comparison of the Light of this lamp with other Lights, that Argand Lamp was used as a standard which is known as such in the experimental room of the Trinity House. It is supposed by some to be above the ordinary Light House Lamp in it’s effect; but having been used as the Standard both in relation to Gurney’s lamp, and the French lamp, and having had its consumption of oil ascertained, no serious error can be introduced by it.

Throwing out of view the first two or three results which were evidently unsafe as data (and simply from the want of experience) I find that the average of several others made at different times gives the light of Gurney’s Quintuple or Trinity Lamp, equal to 13.16 times the light of the standard Argand Lamp. The light of the French Lamp when burning steadily I found to be about 9.5 times that of the Standard; it could be raised higher than this, even up to 10.5, but it was then an unsteady flame, i.e. if left to itself, in less than a minute it diminished very much in it’s brilliancy and light.

In all these experiments of comparison I used the naked Lights, being fully satisfied that the same ratio which Lights hold to each other without the use of Lenses or Mirrors will belong to them, when employed with these adjuncts: provided they are equally applicable as to form, place &c:-

There is one curious philosophical difference in the character of the Quintuple, and the French Lamp which bears directly upon the capability of the former to compete with the latter in point of expence. When the former is burning with it’s common smoky flame, a certain quantity of Oil yields a certain quantity of Light, but when the oxygen is turned on the proportion of Light for the same quantity of oil, or nearly so, rises until it becomes a maximum and then is about five times what it was before. On the other hand when the French Lamp is burning in it’s best state it gives a certain quantity of Light for a certain consumption of Oil, but if the passage of the air be impeded it gives more Light though with a smoky and inconvenient flame. What I mean is, that in Gurney’s lamp a given quantity of fuel is rendered more and more productive of light up to the highest intensity of flame; whereas in the French lamp a given quantity of fuel does not produce the most light at the point of required high intensity. This becomes a set off in the Gurney lamp against the expence of the pure oxygen employed exclusively in it.

I must beg it to be understood that I am giving these conclusions from the results of a comparatively small number of experiments, and would therefore wish this report to be considered as subject to correction, where longer trial and more numerous observations have been made. But tho’ I make this reservation my expectation is that the course of investigation and improvement will increase the power of the Trinity Lamp.

I will now give such data as I can towards estimating the probable current expence of the proposed Light.

The Standard Argand Lamp was found to burn by experiment, 1.0625 pints of Oil in 12 hours, which at the price of six shillings per Gallon would cost nine pence halfpenny. The French lamp according to Drummond’s experiments burns about 16.6 pints in 12 hours⁴, the price of which would be twelve shillings and five pence halfpenny. The quantity of Oil burnt in the Quintuple or Trinity Lamp in 12 hours is 6.54 pints equal in value to four shillings and eleven pence. Such are the relative costs of the fuel for these lamps when ordinary Oil is used. But besides fuel the lamp of Mr. Gurney requires also oxygen and the data are as yet insufficient by which the full amount of expence chargeable upon the Light for this substance, can be ascertained. Up to this time, Native Manganese has been resorted to as the source of that gas; and by Letters from several of the proprietors and agents I find it’s price to vary from £9.0.0 to £10.5.0. per Ton, it’s quality varying probably in proportion. In the experiments made Manganese at £10.- per Ton obtained from Messrs Davey McMurdo & Co⁵ has yielded as the average of many experiments rather above 9 cubical feet of gas, per 14lb of Manganese; hence the cost for Manganese per cubical foot of gas is 1.66 pennies or between six and seven farthings. Now the average consumption of the Quintuple or Trinity Lamp has been 54.8 cubic feet of oxygen per 12 hours, the cost of which in Manganese only would be about Seven shillings and Sevenpence.

But there are other expences incurred in the production of the oxygen; as the wear and tear of the retort; the interest of the original cost of the retort, gasometer &c: the price of the fuel required to produce the oxygen &c: which cannot be estimated until it is known how long a retort will last, and what is the best mode of setting, both for it’s preservation and the economy of fuel. There is scarcely any consumption of fuel for the actual production of the oxygen gas when the retort is once well heated; and I have little doubt that experience would shew that the economy of all three namely, fuel, retort and time, would result from so setting the retort as to preserve it constantly at the working temperature[.]

Against these expences a return may perhaps be found hereafter from the Manganese. For notwithstanding the expulsion by heat of much of the oxygen, it is by no means reduced to that condition, in which theoretically it is left by those who up to this time almost exclusively use it. Hence it may be found of value as an inferior kind of Manganese and return an important proportion of the first cost price, which return must not be left out of view, considering the enormous quantity that would pass through the Light House retorts if the plan were generally adopted.

The gasometer already constructed is calculated to contain 130 cubical feet of gas, and as the consumption in the longest night of 16 hours would not be more than 73 cubical feet of gas, it is abundantly sufficient in size for all ordinary uses. It cost I believe nearly £100. and the interest of this money has to be charged against the lamp. It is not liable to injury or change of any consequence and therefore the cost for wear and tear may be neglected.

The comparison of the price of the light obtained in the common Argand, the French, and the Trinity Lamp, is therefore at present as follows,- At 6s/- per gallon, the Oil required for the Argand Lamp for 12 hours would cost nine pence halfpenny. For the French Lamp the oil required in the same time would cost twelve and five pence halfpenny, which divided by 9.75 the number of times by which its Light appears to surpass the Argand Lamp, would give fifteen pence halfpenny for a quantity of light equal to that of the Argand. With the Quintuple Lamp the cost of Oil per 12 hours is four and elevenpence, and the cost of oxygen (charged from the Manganese only) Seven and Sevenpence, equal to twelve and sixpence, which divided by 13.16 the number of times by which it’s light appears to surpass the Argand will give eleven pence halfpenny for a quantity of Light equal to that of the latter lamps. So far therefore the results stand thus

there being a further unascertained charge against the latter for wear and tear of retorts, cost of fuel and interest of outlay. Now if a light equal to 15 Argands were required; the difference in the cost for the French lamp and Trinity Lamp would be five shillings in twelve hours and this probably would be sufficient to cover the rest of the expence even without looking to the Manganese as a source of return. I beg however that all these comparisons and data may be looked upon as liable to correction by future experiment and improvement. I do not strictly pledge myself to them, but I give them in all sincerity, as the results which now appear likely; on purpose to satisfy the desire of the Honorable Board to know something of the probable applicability of the plan, - and I think it almost certain that continued attempts to improve the apparatus will give the results more and more favorable to Mr. Gurney’s lamp.

I shall conclude this first report by a few general observations respecting the use of the lamp, and the probable improvements in it. In the first place I see no difficulty connected with the nature of the lamp, as to the Keepers giving it proper attention. The Cottons are easily fixed, trimmed, and adjusted by racks; the jets do not get out of order, and if a drop of Oil enters into them they are easily cleaned. If any thing should interfere with the passage of oxygen, still the lamp would burn tho’ with a greatly diminished Light, and it is probable that in such a case, if a chimney were applied, and air blown thro’ instead of oxygen, a very fair light might be obtained, and one which in a case of great emergency might be allowed for a while to occupy the station of the perfect lamp. - As a precaution in case of any derangement giving rise to extinction of the lamp, one upon the French construction could be ready to supply it’s place for the time needful, to restore matters to order.

Mr. Gurney’s plan has already in the Quintuple lamp supplied the power of placing a larger quantity of light, than in the French lamp within a given allowable space, as for instance four inches horizontally, i.e. such a space as will, when allowed to be a focus of light, give a certain degree of divergence to the refracted beams, and yet by the restricted size of the lamp necessarily placed beneath, shall not cut off too many of the rays proceeding from the further side across the lamp in a downward direction. In smaller arrangements it has great advantages in this respect and a Bude Light which gives nearly two and a half times the light of an Argand Lamp, can be placed in the focus of a reflector, just as well as the latter. The arrangements indeed admit of great variation, and in many situations this circumstance alone will probably allow of great facility of adaptation to the conditions of the Light House; as for instance where the light is not required all round the horizon. I have also no doubt that by varying the collocation of the jets nearly as much more Light may be produced within the given space of four inches as is evolved in the present lamp.

It is also highly probable that by experimental investigation the flame will be made both much better, and much cheaper. Already the consumption of oxygen has been reduced in the experiments from 36 to 29 for the same time, whilst the Light has been improved.

With respect to economy in the fuel there seems every reason to expect that Mr. Gurney will succeed in using cheap and common oils as readily in his lamp as the finer kinds; and indeed that with such substances as Rosin Oil, and other highly carbonated compounds, the fuel will not only be much cheaper but may actually weight for weight give a much finer light, because of the quantity of Carbon present.

Again it may not be found always advisable to use pure oxygen for the supply of the jet. Experiment has still to decide whether a mixture of it and air may not be more economical and at the same time sufficiently powerful in evolving light. Another variation which suggests itself to me as probably valuable, is to enclose the flames and the space below, and to send a Current of common air up between them by a blower or by draught, at the same time that oxygen is supplied as now to the interior of each. Such an arrangement would probably greatly facilitate the desired object of packing the greatest number of sources of light into a certain given space.

Besides the Light from the flames of Mr. Gurney’s lamp it does not appear at all impossible that the heat evolved may be employed in heating lime or platina suspended conveniently above the jets, and so a combination of Gurney’s and Drummond’s principles be hereafter effected in one lamp⁶.

The production of oxygen from Nitre also remains open as an experimental question. I have not much expectation that it would be a cheaper source than oxide of Manganese but it might in certain cases be desirable as a quicker method of obtaining gas.

I have only further to add that within these last two days, I have seen Mr. Gurney produce with the present lamp, light equal to 23 and 24 Argand lamps, when common good oil was the fuel used. On using Seal Oil the light was on one occasion raised until equal to 27 Argand lamps. When Naptha was in the lamp a light equal to above 19 Argand lamps was obtained. And when Rosin Oil was used a light equal to 24 Argand lamps was produced. In these experiments no account was taken of the quantity of fuel, and oxygen consumed; the object was to shew the power possessed of evolving a great quantity of Light within a given space. Nothing occurred indicating that with Sperm and Seal Oil the present lamp would not answer; but for the other fuels modifications would be required. The ratio between the gas and oil consumed, and the Light produced in these cases can only be determined by repeated long experiments⁷.

I have the honor to be | My Lords & Gentlemen, | Your most obedient Servant | (signed) M. Faraday.

Royal Institution. | 15th February 1837.