Faraday report to Trinity House   15 January 1838

Professor Faraday’s Third Report, being the Second on the Bude Light. Dated 15th January, 1838.

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

My Lords and Gentlemen,

I have the honor at this time of making a report relative to Mr. Gurney’s lamp, in which I will state the general results of the further experiments and investigations, which I was directed to carry on, in consequence of my former report of the date of the 15th February last². Since that time the lamp has been burning in a practical manner on 49 days, for several hours each day; the manufacture of oxygen being carried on also during the same period, in the same practical manner.

As the present report relates to the use of the same lamp and oxygen apparatus as that formerly described, it will be unnecessary that I should speak more particularly of them, than is needful to connect the present results, with those which have been already given, I will therefore at once proceed to the data obtained since the former report and first to those relating to the production of the oxygen gas.

The Retort described in the last report, was used only twice more; after which Mr. Gurney replaced it, by a new one of larger dimensions. It had been used 22 times: and heated, upon an average, about 8 hours each time; the production of oxygen on each occasion not continuing upon the average for more than 2 hours. It had of necessity been cooled in the intervals, a circumstance which is disadvantageous to the retort as compared to the constant heat which may be retained when in daily use. The amount of oxygen prepared by it was 587 cubical feet; but that is no criterion of the service it might have performed, inasmuch as it might, when once heated up to the due degree, have been used for four, or six hours for the production of oxygen with probably as little injury as for 2 hours. The cost of a retort with setting &c. appears from the bills to be about £10. but in the first place, this is, I think, more than they would cost if many were required; and in the second, as mentioned in the former report, this retort was seriously injured at the commencement in consequence of the setting, through inexperience, being bad.

A new retort was fixed in the beginning of May. It was four feet in length; 8 inches in internal diameter, and an inch in thickness. The feeder for Manganese was placed by Mr. Gurney on the front of the retort out of the way of the fire; and the withdrawal of the exhausted Manganese was much facilitated by using a weighted valve, to close the exit aperture. The stirrer was attached as before.

This retort had been used 48 times and was then sound. For the purpose of economy it was then heated day and night, continually, for 21 days, without making oxygen, except the small quantity required to keep an atmosphere within; at the end of that time it was burnt through. As these 21 days are fully equivalent to 21 heatings, it may be assumed that it has sustained 69 heatings, for so many distinct preparations of oxygen. The quantity of gas prepared by it has been 3206 cubical feet during the 48 times of evolution, or upon an average 66.8 [cubic] feet each time. But as before remarked, probably, twice or three times this quantity might have been prepared at each period with no additional injury to the retort. Still, using the data really obtained, and allowing that £10. may be a full price for a retort and setting, it would appear that each generation of gas in this case cost 2s/10d¾ as retort expence. It is however but one case; and, though I cannot assert it, I should expect that when more extensive experience had given more information as to the casting, setting, heating &c, the average retort expence would be much less that this, perhaps not more than one half.

When the retort has been at a fair working heat, it has taken about two hours for the evolution of 60 cubical feet of gas. As it will be seen further on that the lamp would, when giving the light of 21 Argand lamps require about 120 cubic feet of oxygen for 16 hours; so it may be remarked here that four hours is time sufficient to work off that quantity of gas, by one retort only.

The Fuel used to heat the retort has been coke. A considerable consumption of this article has occurred in bringing the retort, at each separate operation, from a cold state to the degree of heat required, before any oxygen could be evolved; and on this point I have already given an opinion that it would be better for the retort, and more economical as regards fuel, to keep the former continually red hot; as is indeed the case in modern gas works. But it is my duty to give the facts as they are. Now the first chaldron of coke heated the retort 25 times; the second 22 times; and the third 13 times, and 24 days and nights, which together may be taken as equal to 37 times. Thus 3 chaldrons of coke were competent to 84 heatings; and as the price was 19/-s per chaldron, the average cost of fuel per heating was 8 pence.

The last chaldron of coke illustrates the economy that would result from keeping the retort continually hot. As the two first chaldrons heated the retort 25 and 22 times, it may be admitted that the 13 heatings by the third chaldron had consumed at least one half of it. Yet the other half was able to keep the retort at working heat for 24 days and nights in succession and would have made a full proportion of oxygen each day. So that in fact when so applied, the cost of fuel for each operation, or rather each day, is only the twenty fourth part of 9s/6d or four pence three farthings.

The gasometer is in the same condition as at first and is not liable to serious or rapid decay. With respect to it the expence is principally the Interest of the money laid out, that being about £100.

The oxygen has been mostly obtained from Manganese supplied by Mac Murdo and Co³:- but some has been prepared from Manganese supplied by Messrs. Williams & Co⁴:- of Devonshire. The following are the general results obtained up to this time.

I believe the prices are all higher than they would be on a great scale; but taking them as they stand, it would appear, that the Warwickshire Manganese is the most economical. It is also the most advantageous in this respect, that it gives more oxygen, weight for weight, than the other varieties; so that a smaller quantity of material has to be moved at first, and worked through the retort in the manufacturing operations. I am not aware as yet whether it is so circumstanced, that the carriage of it to various places would cost more than that of the Devonshire. The supply also of it may be limited.

<-><-><->

I will now proceed to consider the lamp and light. The lamp is the same as that described in the last report, and had five wicks, each with three oxygen jets, and a sixth centre wick with a single jet; but in place of burning it with such supply of oil and oxygen as would give a light equal to 12 or 13 Argand Standard lamps, an increased proportion of both was allowed, so as to obtain more light from the same lamp in the same space; an important object just touched upon at the close of the last report.

The proportion of light obtained in these experiments at very different times has varied from 16, to above 26 times, that of the standard Argand Lamp; and the average of 15 estimates on different days of burning is 20.866 Argand Lamps. Hence the proportion as to light produced stands thus,

The number of days upon which the lamp has been burning, (the consumption of oil and oxygen at the same time being ascertained experimentally) has been 49.The number of hours during which the lamp has burnt has been 365½, in periods varying from 4 and 5 hours up to 10 and 11. The quantity of oil burnt in that time has been 268½ pints; and the quantity of oxygen consumed 2720½ cubical feet.

Taking an average of the various results it would appear that the lamp when burning and giving the light of 20.86 standard Argand Lamps, would, in 12 hours consume 8.8 pints of oil, and 89.31 cubical feet of oxygen. The price of the oil at 6s/10d per gallon is 7s/6d.The price of the oxygen is, for Manganese, (when that from Warwickshire was used) 11s/5d½; for fuel, one heating -s/8d; and for one 69th share of the value of the retort and setting 2s/10d¾; making altogether 22s/6d.

To compare the expence with that of light from the common Argand and the French lamps, let us observe, that the Argand lamp consumes 1.0625 pints of oil, in twelve hours; which at 6s/10d per gallon, is worth 10.89 pence. The French lamp consumed 16.6 pints in twelve hours; which are worth 14s/2d. Thus,

or making the light in each case equal 1 Argand lamp, then that light from

This result, which is so much in favour of the Gurney lamp, is the more important because it includes the expence due to fuel, and the fair proportion of retort charge, which I could not introduce on the former occasion. The only expence incurred and not included, is the interest of the value of the Gasometer, and Lamp (about £120 together) and their wear and tear. It must still be borne in mind that the expence of retort and fuel will probably be much diminished; and, further that as I before observed, the Manganese, though exhausted as far as the action of heat is concerned will probably find a market in consequence of still being able to produce chlorine, and after some trial perhaps by the bleacher, may return a fourth or more of it’s first cost. It will be observed that the expence of the Argand and French lamp is estimated at a higher rate in this report than in the last. That is, because I took the price of oil on the former occasion at 6s/- per gallon, but find that it has cost 6s/10d; which latter price has been calculated upon in the present report.

I have also in the estimate just made, taken the oxygen at the price which it cost with Warwickshire Manganese. But now for the sake of giving the worst view of the Gurney lamp, I will take the dearer oxygen obtained from Mac Murdo’s Devonshire Manganese, at the London price i.e. 16s/5d per 100 cubical feet of oxygen and will also take the oil at only 6/-s per gallon: Then

or making the light equal to one Argand lamp,

<-><-><->

The general observations respecting care, attention &c. &c. which were made in the former report, still hold good, nor have I much to add to them. The lamp burns with considerable regularity; and though if neglected, little carbonaceous cones occasionally form on the summits of the jets, which cause the proportion of light to fall, they are easily removed when observed, and avoided altogether by a proper adjustment. The lamp will burn for three or four hours at a time without needing attention, and is on the whole, quite as independent of the watchman as the usual Argand lamp.

I have had a few experiments made with cylinder glasses for the purpose of protecting the flame from wind should it be needful, and I find that they do not sensibly diminish the light.

I think that the lamp and apparatus in its present form, has now been tried as far as it conveniently can be, by anything short of actual practice in the Light House. I have given my most careful thought and attention to it, that no exaggerated results should creep in and mar the conclusion: and my belief is that I rather underrate than overrate the lamp. Still I cannot but suppose that regular Light House practice would shew many things which the experiments made have not brought into view, and must ask the indulgence of the Board on that account.

I have received notice from Mr. Herbert that Mr. Gurney has sent in a new lamp, still dependent on the principle of introducing oxygen into the flame. When subjecting this lamp also to examination, I shall not think it necessary to go any further into the question of the production of oxygen gas; for though no opportunity shall be lost of ascertaining such points respecting it, as may be within reach, still it may be advisable to avoid as much as possible the expence of manufacturing oxygen upon a very large scale⁵.

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

Royal Institution | 15th January 1838.