1839.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



.329 



commonly taken us the standard. I do not think it entitled to this 

 pre-eminence : for it may be made to emit very different qnantities of 

 light, according to differences in the natnre and supply of the oil, as 

 well as variations in the form and position of the chimney. Besides, 

 such lamps are too rare in this country to be selected as standards of 

 illumination. 



After comparing lights of many kinds, I find every reason to con- 

 clude, tliat a large wax candle of three to the pound, either long or 

 short, that is, either 12 or 15 inches in length, as manufactured by one 

 of the great wax-chandlers of London, and furnished with a wick con- 

 taining 27 or 2S threads of the best Turkey cotton, is capable of fur- 

 nishing a most uniform, or nearly invariable standard of illumination. 

 It affords one-tenth of the light emitted by one of (he Argand lamps 

 of the Trinity House, and one-eleventh of the light of my mechanical 

 lamp, when each lamp is made to burn with its maxiuunn Hauie, short 

 of smoking. 



The great obstacle to the combustion of lamps, lies in the viscidity, 

 and consequent sluggish supply, of oil, to the wicks ; an obstacle nearly 

 insuperable with lamps of the common construction during the winter 

 months. The relative viscidity, or relative fluency of different liquids 

 at the same temperature, and of the same liquid at different tempera- 

 tures, has not, I believe, been hitherto made the subject of accurate 

 researches. I was, therefore, induced to make the following experi- 

 ments with this view. 



Into a hemispherical cup of platinum, resting on the ring of a che- 

 mical stand, I introduced 2000 water-grain measures of the liquid 

 whose viscidity was to be measured, and ran it off through a glass 

 syphon, i of an inch in the bore, having the outer leg 3i inches, and 

 tlie inner leg 3 inches long. The time of efflux became the measure 

 of the viscidity ; and of two liquids, if the specific gravity, and con- 

 sequent pressure upon the syphon, were the same, that time would 

 indicate exactly the relative viscidity of the two liquids. Thus oil 

 of turpentine and sperm oil have each very nearly the same density ; 

 the former being, as sold in the shops, = 0.S7G, and the latter from 

 0.87G to 0.880, when jiure and genuine. Now I found that 2000 grain- 

 measures of oil of turpentine ran off through the small syphon in 95 

 seconds, while that quantity of sperm oil took 2700 seconds, being in 

 the ratio of 1 to 2Si ; so that the fluency of oil of turpentine is 28^ 

 times greater than that of sperm oil. Pyroxilic spirit, commonly called 

 naphtha, and alcohol, each of specific gravity 0.825, were found to run 

 off respectively in SO and 120 seconds; showing that the former was 

 50 per cent, more fluent than the latter. Sperm oil, when heated to 

 205"^ Fahr., runs off in 300 seconds, or one-ninth of the time it took 

 when at the temperature of 64^. Southern whale oil, having a some- 

 what greater density than the sperm oil, would therefore flow off faster, 

 were it not somewhat more viscid. Its specific gravity is 0.92G, and it 

 takes just the same time to flow off as sperm oil, either in its cold 

 state or heated to 2G5^. 



2000 grain-measures of water at 60° run off through the said syphon 

 in 75 seconds, but when heated to 180° they run of! in 61. 



In llie adjoining figare, A, A, B. B, is a seclion 

 of the cylinder, which constiUilcs llio ciytoni ; 

 the oil teing contained between iKo inner and 

 outer cylindeis. anil receiving heat from llu' flame 

 olilie lamp, «!iich passes up ihiougli the inner 

 cylinrler, li, B, and is reveiberatod more (jr less 

 against its sides by the lop of the iron cliiiimey 

 C, be ng notched and bent back. D is a slop 

 cock which is opened to allow the oil to descend 

 to the wick, and is .shut when the cistecrt is lo l;e 

 separated from the pipe of supply, K, lor the 

 puipo,5e of re-charg'ng it with oii. Ihellanicis 

 111 Hiilied, not by i-iusing or lowering llie wick, as 

 ill couinion lamps, Uii Ijy raising or loweing the 

 bell-mouthed glass chimney, uhicli rests at iis 

 boltiim on three points, and is moved by means 

 of the r.'.ck-work' meclianijNm F. The concentric 

 cyiindiic sp.ice. A, A, & B. B. contains a [lint iiii- 



fjcrial, and sliould be made entirely lud before 

 ighiiiig the lamp; so as to leave no air in the 

 cistern, wfilcli by its expansion with the heat, 

 would inevitably cause an overllow of the lil. 



Concentrated sulphuric acid, though possessing the great density of 

 1.S40, yet flows off" very slowly at Gl', on account of its viscidity ; 

 whence its name of oil of vitriol. 2000 grain-measures of it took 660 

 seconds to discharge. 



Mr. Samuel Parker, long advantageously known to the ]jublic for his 

 sinumbral, and pneumatic fountain lam])s, as well as other inventions 

 subservient to domestic comfort, having recently obtained a patent for 

 a new lamp, in which the oil is heated, by a very simple contrivance, 

 in the cistern, to any desired degree, before arriving at the wick, I 

 instituted an extensive series of experiments to determine its value in 

 the production of light, and consumption of oil, compared to the value 

 of other lamps, as well as candles in these respects. 



The following arrangement was adopted in these experiments for 

 determining the relative illumination of the different lights. Having 

 trimmed, with every precaution, my French mechanical lamp, and 

 charged it with pure sperm oil, I placed it upon an oblong table, at a 

 distance of 10 feet from a wall on which a sheet of white paper was 

 stuck. One of Mr. Parker's hot-oil lamps, charged with a quantity 

 of the same oil, was placed upon the same table ; and each being made 

 to burn with its maximum brilliancv, short of smoking, the relative 

 illumination of the two lamps was determined by the well-knowix 

 method of (he comparison of shadows ; a wire a few inches long, and 

 of the thickness of a crow-quill, being found suitable for enabling the 

 eye to estimate very nicely the shade of the intercepted light. It was 

 observed in numerous trials, both by my own eyes and those of others, 

 that when one of the lamps was shifted half an inch, nearer to or 

 further from the paper screen, it caused a perceptible difference in 

 the tint of the shadow — Professor Wheatstone kindly enabled me to 

 verify the precision of the above method of shadows, by employing, in 

 some of the ex|)eriments, a photometer of his own invention, in wdiicll 

 the relative brightness of the two lights was determined by the rela- 

 tive brightness of the opposite sides of a revolving silvei'ed ball, 

 illuminated by them. 



1. The mechanical lamp was furnished with a glass chimney 1.5 

 inches in diameter at the base, and 1.2 at top; the wide bottom part 

 was 1.8 inches long, and the narrow upper part 8 inches. Wlien 

 placed at a distance of 10 feet from the wall its light there may be 

 estimated as the square of this number, or 100. In the first series of 

 experiments, when burning with its maximum flame, with occasional 

 flickerings of smoke, it emitted alight equal to that of 11 wax candles, 

 and consumed 912 grains of oil per hour. The sperm oil was quite 

 pure, having a specific gravity of 0.874 compared to water at 1000. 

 In a subsequent series of experiments, when its light was less flicker- 

 ing, and ecjual only to that of 10 wax candles, it consumed only 815 

 grains, or 0.1 164 of a hb. per hour. If we multiply this number into 

 the price of the oil (Ss. per gallon) per lib. Ik/., the product 1.2804(/. 

 will represent the relative cost of this illumination, estimated at 100. 



2. The hot-oil lamp burns with a much steadier flame than the me- 

 chanical, which must be ascribed in no small degree to the rounded 

 slope of the bell-mouthed glass chimney, wdiereby the air is brought 

 progressively closer and closer into contact with the outer surface of 

 the flame, without being furiously dashed against it, as it is by the 

 rectangular shoulder of the common contracted chimney. When 

 charged with sperm oil, and made to burn with its maximum flame, 

 this lamp recjuired to be placed one foot further from the screen than 

 the mechanical lamp, in order that its shadow should have the same 

 depth of tint. Hence, its relative illumination was, in that case, as 

 the square of 11 to the square of 10 ; or as 121 to 100. Yet its con- 

 sumption of oil was only G96 grains, or somewhat less than 0.1 of a lib. 

 per hour. Had its light been reduced to 100, it would have consumed 

 only 576 grains per hour, or 0.82 of a lib. If we midtiplythis number 

 by lid. the product O.'Mid. will represent the relative cost of 100 of 

 this ilhiiniuation. 



3. The hot-oil lamp being charged with the southern whale oil, of 

 specific gravity 0.92G, at 2s. Grf. per gallon, or 3id. per lib,, when 

 burning with its maximum flame, required to be placed 9 feet and 1 

 inch from the screen to drop the same tint of shadow upon it as the 

 flames of the other two lamps did at 10 and 11 feet with the sperm 

 oil. The square of 9 feet 1 inch=;82 is the relative illumination of 

 the hot-oil lamp with the southern whale oil. It consumed 7S0 grains, 

 or 0.111 of a pound per hour; but had it given 100 of light it would 

 have consumed 911 grains, or 0.130 of a pound, which number being 

 multiplied by its price 3'iU., the product 0.4875rf. will represent the 

 relative cost of 100 of this light. 



4. A hot-oil lamp charged with olive-oil of specific gravity 0.914, 

 at 5s. 6(/. per gallon, or 7id. per lib., when bnniing with its maximum 

 flame, reipiired (o be placed at 9 feet 6 inches to obtain the standard 

 t lilt of shadow upon the screen. I( consumed 7()0 grains per hour. 

 The square of 9A feet is 90i, which is the relative intensity of the 

 light of this lamp. Had it emitted u light = 100, it would have coH' 



2 B 2 



