120 



UNDULATORY FORCES. LIGHT. 



[AMJJ.TSIS or oou. OA*. 



iU composition by the following process: Collect a 

 quantity of gas in a graduated tube over quick.-.: 

 introduce a solution of caustic potash, ami agitate it 

 with the gas for some minutes ; then allow the tube to 

 stand for a short time, and observe how much carbonic 

 acid has been absorbed. After this has been done, pass 

 up a concentrated solution of pyrogallic acid in potash, 

 or, better still, a small quantity of the powdery crystals 

 of pyrogalliu acid itself ; shake the tube again, and 

 having allowed it to stand for a few minutes, read off 

 the bulk of oxygen that has disappeared; transfer the 

 gas to another tube over water, and by means of a 

 syringe, or other contrivance, introduce a small quantity 

 of bromine, or its strong solution ; shake the tube for a 

 minute or so, and observe that the bromine is in suffi- 

 cient quantity to give the gas an orange-red colour; 

 after the lapse of four or five minutes, pass up a solu- 

 tion of potash, and shake again. In this way the excess 

 of bromine will be absorbed ; and on allowing the tube 

 to stand for a short time, the amount of condensible 

 hydro-carbon may be determined by the loss in bulk. 

 Transfer the gas to another tube, and agitate it with a 

 solution of dichloride of copper in muriatic acid (this is 

 made at once by mixing equal parts of black oxide of 

 copper and recently precipitated copper, with hydro- 

 chloric acid). After a few minutes, the solution is to 

 be withdrawn, and the gas washed with potash; the 

 loss in bulk indicates the quantity of carbonic oxide 

 present. Lastly, a portion of the residual gas is to be 

 transferred to an eudiometer, and mixed with about 

 twice its bulk of oxygen ; and the mixture is to be fired 

 by the aid of an electric spark. After standing for a 

 few minutes, the loss in bulk is to be observed ; a solution 

 of caustic potash is then to be passed up into the gas, 

 and the absorption of carbonic acid noted. This indi- 

 cates the amount of light carburetted hydrogen present ; 

 and then by subtracting twice this volume from the 

 total amount of diminution caused by the detonation, 

 we obtain a number, two-thirds of which represent the 

 hydrogen of the gas. Lastly, the residual gas, from 

 which the portion for the oxygen experiment was taken, 

 is to be mixed with about four times its bulk of pure 

 chlorine, and exposed for some hours to daylight, or for 

 a moment or two to sunlight, and then washed with 

 potash the residue is nitrogen. In this way we may 

 obtain an estimate of the proportions of the chief con- 

 stituents of coal gas. These, however, vary to the 

 following extent : 



Light carburetted hydrogen, from 35 to 52 per cent. 



Hydrogen ... 25 52 



Carbonic oxide 

 Carbonic acid 



IP 



tygen 



9 

 4 



2 

 8 

 20 



' sperm ; and, consequently, the latter is now almost 

 , always employed. Sometimes the comparison is made 

 with one candle ; Dr. Letheby uses two, and Mr. Evans 

 employs three. A jet of gas composed of hydrogen and 

 olehant gases, inixoJ in the proportion of nine of the 

 former to one of the latter, has been proposed as a stan- 

 dard of constant value ; but the use of it is very inconve- 

 nient : and, lastly, Mr. Lewis Thompson has suggested 

 the employment of paraffiue. 



Finally, it ought to be stated, that whenever the 

 quality of gas is estimated by any of these methods, it 

 ought to be consumed from the burner or jet which is 

 best fitted for its combustion. If this is not attend..! 

 to, a discrepancy to a large extent may arise between two 

 different experimenters. As a rule, common gas requires 

 a larger aperture for combustion than cannel ; and high 

 glasses, or chimneys, are apt to lower the illuminating 

 power of the former, and to raise that of the latter. 

 Different experimenters have exhibited different fancies 

 with regard to this part uf the subject : for example, Mr. 

 Wright prefers a single jet, one-eighth of an inch in dia- 

 meter, for his investigations ; Dr. Fyfe makes use of a 

 Winfield or Aberdeen burner ; and in London, the burner 

 fixed by Act of Parliament is ah Argand of sixteen holes, 

 with a seven-inch chimney, consuming five cubic feet per 

 hour. There is no doubt, however, that in many cases a 

 fish-tail or bat's-wing will afford the best light for testing 

 purposes. We append the following table, to show how 

 much the character of the burner affects the quality of 

 the results obtained : 



Burner. 



Jet five inches high . 

 Small fish-tail . . . 

 Large ditto . . . 

 Small bat's-wing . . 

 Large ditto . . 

 Argand of forty holes 



Nitrogen . 



Condensible hydro-carbons 



The approximative or commercial value of coal gas is 

 determined in several ways : thus 



1st. By meant of the Photometer. This we have al- 

 ready alluded to ; and it is only necessary to say here, 

 that the methods employed are four-fold namely, Count 

 K u in ford's plan, with shadows ; Ritchie's, with his in- 

 strument that has two reflecting surfaces and a screen in 

 a dark chamber ; Wheatstone's, which consists of a me- 

 chanical contrivance, whereby a silver bead is made to 

 revolve in such a manner as to produce a geometrical 

 figure with two outlines ; and, lastly, the plan usually 

 employed, which is that of fiunsen's, with a waxed screen 

 ana a graduated rod a description of which has already 

 been given. Some doubt exists as to the kind of illu- 

 minating standard which ought to be adopted. Originally 

 the standard was a mould caudle of six to the pound ; 

 but there are so many objections to its use that it has 

 long been discontinued. Dr. Frankland employs a com- 

 posite candle; Dr. Fyfe prefers one of wax; and tho 

 standard which is specified in most of the Acts of Par- 

 liament relating to the subject, is a wax candle of six to 

 the pound, burning at the rate of 120 grains per hour. 

 In general, however, it is found, that there are more 

 irregularities with the combustion of wax than with 



In cubic feet. Pw- 



100 



1-98 

 200 

 3-00 

 400 

 4-50 



1-00 



400 



440 

 840 



784 



pom 



per foot. 



1-00 

 145 

 1-53 

 1-46 

 1-87 

 174 



These results were obtained by Dr. Fyfe with cannel 

 gas; and they show that the large bat's-wing produces a 

 flame that, for equal consumption, is nearly twice as 

 powerful as that with the single jet. 



Again, the quantity of gas consumed per hour in the 

 same burner will affect the results ; thus 



Consumption 



Burner. per hour 



In cubic feet. 



Power of gu 

 per foot. 



Argand, with seventy-two holes . . 7~0 . . 6-57 

 . . 5-0 . . 6-60 



3'3 . . 340 

 From which it is manifest, that in ascertaining the illu- 

 minating power of gas, great judgment is necessary, both 

 in the selection of the burner and in the rate of con- 

 sumption, in order to obtain fair and proper results. 



2nd. The Chlorine test is very much appreciated by 

 Dr. Fyfe. It was originally proposed by Dr. Henry, 

 and in his hands it afforded very accurate results. The 

 objection to the test is its inconvenience ; for chlorine 

 takes a long time to prepare, and we are never certain 

 of its being pure. Besides which, it is an unpleasant gas 

 to inhale ; and, escaping into the laboratory, it produces 

 the most serious injury to the brass and iron- work of 

 chemical apparatus. The mode of conducting the expe- 

 riment is this : A quantity of gas is to be let up into a 

 graduated tube over water ; the tube is then to be covered 

 so as to exclude light, and chlorine is to be passed up 

 into it. After standing for ten or fifteen minutes in the 

 dark, the excess of chlorine is to be absorbed by potash, 

 and the amount of absorption read off. The larger the 

 quantity absorbed, the better the gas. This will range 

 from three to twenty per cent. The matters absorbed 

 by the chlorine are the condensible hydro-carbons, which 

 are the illuminating principles of the gas. 



3rd. The Bromine Tett. Many years ago, M. Balard 

 showed that bromine had the power of absorbing ole.li.-tnt 

 zas, and that in this respect, as in most others, it was 

 like chlorine. Lately, Mr. Lewis Thompson has taken 

 advantage of this property, and has made it tiio means 



