Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/109

Rh GAS Flat-flame burners, or burners-which spread their ﬂame in a broad thin sheet, are of two principal kinds known respectively as “ﬁshtail” (ﬁg. 21) and “ batwii1g” (ﬁg.
 * 32) burners. The ﬁshtail or union burner has two oriﬁces

drilled in its surface, which ai'e inclined to- wards each other at an angle of 90°, so that the issuing cur- rents impinge and spread the ﬂame in a broad sheet. The gas in the batwing issues from a narrow slit cut right across the Sm.faCe_ In the Fics. 21, 22.—F1at-ﬂame Burners. best forms of all kinds of burners new in use steatite or ad-amas (pottery) tops are employed. In Sugg’s Christiania burner the slit is circular, and the light issues in two thin sheets which coalesce in their upper luminiferous part, pro- ducing a most beneﬁcial result when common gas is con- sumed. The coiniiiou metal and steatite-tipped burners in use permit the current of gas to strike against their oriﬁces without any control or regulation, but in the numerous patented forms of both ﬁshtail and batwirig jets certain mechanical obstructions, or small governors, are inserted, which break or retard the current. Screws, wire gauze, calico, cotton wool, iron ﬁlings, and constriction of the lower part of the burner are all devices in use. Of all these one of the simplest and most effective is the plan on which the Briinner burner is constructed, which is simply to have the opening at the lower part of the burner smaller than the upper oriﬁce. For different qualities and pressures of gas the Brijnner burner presentsa great variety of combina- tions by having several distinct sizes of lower constriction which can be adjusted to a large number of tip oriﬁces. Tlins, with six distinct openings at each end, 36 combina- tions can be made. As Argand burners are not suited for measuring the illuminating power of rich cannel-gas, ﬂat tlame—bui'ners have to be employed; and in the Act of Parliament under which the Glasgow Corporation supplies gas, it is provided that “all the gas supplied by the corpora- tion shall be at least of such quality as to produce from a union jet burner, capable of consuming 5 cubic feet of gas per hour under a pressure equal to a column of water '5 of an inch in height, a light equal in intensity to the light produced by 25 sperm candles ')f 6 in the pound, burning 120 grains per hour.” _ Dr 'allacc, in a coiiiiiuniication on the “ Economical Combus- tion of Coal-Gas ” (Proc. Phil. Soc. (ll rsgow, vol. ix.), tabulates an e'tensive series of experiments made with ﬂat-flame burners of '.u'ions sizes with about 28-candle gas at different degrees of pressure. 'l'lic general result of these experiments shows that, to obtain the higlicst lnminiferons effect with burners of small aperture, :1 low pi-essiii-n of gas (not more than_'5 inch) must be maintained, although, as the size of the jet increases within certain limits, the pressure may be increased with favourable i'esults. With 9 sizes of Bray’s regulator ﬁshtail (a buriie1' having an obstruction consisting of a double fold of COLt0Il cloth) Dr Wallace obtained the followinrr results, calculated to 5 cubic feet per hour :— ' D I. Bll!'l1C1‘01l23-1 5 0 7 s At §—inch pressure .... .. 14'-3,17--1 20-0 230 25-0 20-15 27-0 29-10 2s0s Atl-inch. .... .. 11-7 13-3 17-0 20-0 23-0 -20-2 -2.3-7 30-2 3-20 At lg;-inch ,, .... .. s-s_ 9-sli3-9li7-:1 19-4 -23-7 -2.5-9 ;:asblos I "' I ‘ The gas used in_ the -.5-inch experiments was 2772-caiidle standard, for the 1—iiicli series it was 2905, and for the 1.‘_.-inch s -t it vims 28131-candle. V1th 30 combinations of Brenner burners l)r Wallace obtained from 28'2-candle gas at 1 inch pressure an avei'age of 257, and at 1%-inch 25'8-candle power, most of the combinations giving fairly equal results, Of all burners the ordinary fishtails, and they a1'e the most fre- quently used, give the most inferior i'esnlts when used for burning common eo.1l—gas. The results tabulated below are derived from 99 the series of experiments by Mr Pattinson of Newcastle already quoted. The experiments were made with 1410-candle gas, from which it must be remembered 17'86-candle power was developed in Sugg’s improved London Argand :- Cubic {e t 11] ininal' Illuminating Perhouii. - uP0wei-.mg p°;:;.r]'$u{:._“' Fishtail, No. 3, stcatite top 4 3'0 3'75 ,, ,, metal top .... .. 3'5 4'10 5'85 ,, No. 4, stcatite top.... 4'9 5'20 5°31 ,, No. 5, ,, 5'0 7'80 7'80 Batwing, metal top ............. .. 5'0 9'26 9°26 Fishtail, Bray’s, No. 4 ........ .. 4'0 5'02 6'28 ,, ,, No. 8 ........ .. 5'0 11'80 11'80 ,, ,, ,, ........ .. 7'0 14"21 10'15 Batwing, l}ri3iinci"s, No. 4 4'0 10'10 12°62 ,, ,_, ,, .... .. 5'0 11'60 11'60, , Sngg’s, , , .... .. 4 '0 8 '40 10 '50 ,, ,, ,, .... .. 5'0 10'90 10'90 From these experiments it appears that there are burners in com- mon use which, consuming the same amount of gas, differ in light- giving effect from 3'75 to 12'62-candles, one giving more than three times as much light as the other ; -and if we take the best Argand bnriier into account, the range of variation is from 3'75 to 17'80, or as one to ﬁve nearly. Another important deduction from these observations is that large-sized burners as a rule give much more illinninating power than the smaller sizes. Thus a burner passing 7 feet of gas per Iiour will almost invariably distribute more light than two each burning 3'5 feet. Gas Test2'ng.—The universally recognized and practised method of valuing gas is by comparing its light with that yielded by a standard light, which can be obtained as nearly as possible of an unvarying intensity. In making such a photometric,comparison it is essential that the conditions under which the lights to be compared are burned shall be uniform, and that the materials be consumed at a deﬁnite rate. The standard recognized by legislative authority in Great Britain and America is the burning of a sperm candle 6 to the II). consuming at the rate of 120 grains of sperm per hour, compared with gas burning at the rate of 5 cubic feet per hour. The burner prescribed for common gas is the Sugg-Letheby-Argand, in Acts of Parliament deﬁned as a l 5-holed Argand with a 7-inch glass chimney ; and for rich cannel-gas a union or ﬁshtail jet passing 5 feet per‘, hour is employed. The apparatus employed for making the com- parison is generally the Bunsen photometer, or some modi- ﬁcation of that instrument; and the ratio of comparative illumination is established by the well—known principle that the intensity of light diminishes in inverse proportion to the square of the distance from its source. The Bunsen photo- meter consists of a bar of wood 98 inches long, with a candle holder at one end and at the other the standard gas burner. A balance for weighing the candle as it burns, an indexed meter for the gas, and a clock are also provided. The bar is graduated from the centre to each end, and on it is set a sliding holder into which a screen of prepared paper is placed. The screen is so prepared that a spot or disc is more opaque than the remainder of the paper, so that when light passes through it from one side, that particular spot is seen distinctly darker than the rest. Vhen, how- ever, equal amounts of light fall on it from both sides the spot disappears, and the whole surface presents a uniform appearance. Therefore, with both candle and gas burning under the stipulated conditions in a darkened chamber, by moving the screen on the graduated bar from the one light and towards the other till the da1'k spot on the paper dis- appears, the comparative illnminating power of the light is ascertained by the position of the screen on the graduated bar, or by a simple arithmetical calculation. ‘Thus, the lights being 100 inches apart, if at the conclusion of the experiment the screen is 20 inches from the candle and 80 from the gas jet, since 80‘-’ is 16 times 209, the gas is 16- candlc power.