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tions, with the synonyms and several varieties. There is much propriety in presenting some of the changes, observing at the same time that this species had been called in our country, to 1857, C. anceps, Muh. C. laxiflora, Lam., 1789, not of Schk.

Boott, Illus. Car., No. 87, Tab. 89, 1858.

Gray, Man. Bot., p. 524, 1857.
C. heterosperma, Wahl., No. 67, 1803.
C. striatula, Mx., vol. ii, p. 173, 1803.
C. anceps, Muh., Letter to Willd.

Willd., vol. iv, p. 278, 1805.

Schk., Tab. Fff., fig. 128, 1812.
C. plantaginea, in part, Schk., Tab. Kkkk, fig. 195, 1812, not
Lam.

Muh. Gram., p. 242, 1817, not Lam.
C. anceps, Muh. Dewey, Sill. Journ., vol. x, p. 36, 1826.

Tor. Mon. Cyp., p. 414, 1836, and Am. Auth., var. palulifolia, Dew. Carey Ed. 1, and Man. Bot., 1857, and var. plantaginea, Boott, both Schk., fig. 195.

This case shows us the principal cause of the numerous synonyms in Caricography, viz., their being named by different botanists in different places and unknown to each other. In so large a genus, embracing more than eight hundred species, in all quarters of the globe, this multiplication of names may easily occur. This species was named by authors in different parts of the world, who knew not those already given. Hence, all the names were correct and legitimate, except the reference of this species in Muh. Gram. to C. plantaginea. Interesting as is the correction by Dr. Boott, the point attained shows only the author of the original or first name.

Again; where the so-called variety requires as long, or nearly as full a description, as the species itself, there is no objection to giving it the rank of a species, till it is proved that both forms are produced from the same seed or the one changes into the other in growing. In the well known varieties, as some have called them, this proof has not been attained in one case of a hundred. Some have been called varieties and so described for years, when they have been raised to the place of species, and continue to hold their rank. Besides the instance of C. gynandra, already noticed, there are others equally obvious and certain.

For these reasons, it is difficult for me to adopt two of the varieties of this species in Dr. Boott's splendid “ Illustrations," viz., C. styloflexa, Buck., and C. blanda, Dew. Indeed, it needs but little extension of the specific description to comprehend two or three other and admitted species. SECOND SERIES, Vol. XXVII, No. 79. ---JAN., 1859.

ART. XIII.- On the Variable Illuminating Power of Coal Gas;

by WILLIAM E. A. AIKIN, Prof. Chem., &c., University of Marylaud.* (Read before the American Association for the Advancement of Science, at

the Baltimore Meeting, May, 1858.) In common with a large number of our citizens, my attention was directed some short time since, to a somewhat sudden, inexplicable and enormous increase in the amount of our quarterly bills for gas consumed; an increase equal at times to an advance of a hundred per cent over the corresponding quarter of the preceding year. As it would have been absurd to suppose a simultaneous derangement of all the meters over an extensive district, it was obvious that the difficulty could not lie in any error in the registry of the gas, but in its illuminating power, necessarily requiring the consumption of a greater bulk of gas to produce a given quantity of light. Feeling curious to know how this difference could have occurred, I set myself to work to ascertain, if possible, what causes could be acting to diminish the illuminating power of the gas.

It has long been known that the quality of the gas produced from the fat coals is very materially influenced by the circumstances of the decomposition. In the elaborate experiments made some years ago on a most extended scale by Hedley, the British Engineer, as detailed in his report to a committee of the House of Commons, we find this subject most satisfactorily discussed. Below a cherry red heat the products obtained by heating coal in close vessels contains hardly any illuminating material. At that temperature it is furnished most freely, but after having been formed is liable to decomposition, involving a loss of carbon by contact with any highly heated surface in passing through the apparatus. Such decarbonization increasing with the degree of heat, with the extension of the red hot surface, and with the time of contact. Again, the duration of heat is most important, the best gas coming over during the first hour, the quality rapidly deteriorating, until at the expiration of four hours the product is worth very little to the consumer, and after five hours may be considered as worthless. But the bulk of such worthless gas that can still be obtained by pushing the process to completion is very considerable, equal sometimes to of all that passes over.

How far any neglect in the observance of the precautions re. quired to produce a proper illuminating gas, may explain the result the public have no means of knowing. All that we know

* The title of the above paper was accidentally omitted when the list of papers read before the Association was published in the July No. of this Journal.

is that the manufacturers furnish an article which they say is the right article and prepared in the right way, and possessing an illuminating power varying from 14 to 17 candles. That is, their engineer reports, that on trial with a photometer, at stated times, the gas burning from a jet, consuming five cubic feet per hour, gives an amount of light equal in the average to that of 15 patent candles six to the pound. The patent candle being ostensibly a mixture of sperinaceti and wax. Assuming as true all that is claimed by the manufacturers, it can still be shown that the gas even if properly made and correctly tested may be and is furnished to the consumer in a condition of greatly diminished illuminating power, compelling the consumption of a greater bulk to obtain the required light and consequently swelling the record of the meter and the sum total of the quarterly bills. In my trials to determine the specific gravity of our gas by weighing a globe previously exhausted and then filled with it, I obtained a result ranging from •570 to ·580 somewhat below that given as characterizing good gas. But in reality I attach very little importance to this result since the mere specific gravi. ty of such a complex mixture as coal gas can hardly be relied upon to determine its commercial value.

Although good gas certainly has a higher specific gravity than poor, yet the difference could not be taken to represent the true difference in value since the principal components of the mixture hydrogen, carbonic oxyd, light carburetted hydrogen, olefiant gas and other still heavier hydrocarbons having specific gravi. ties, widely different, right vary somewhat in their relative proportions sufficient to affect the illuminating power, without at the same time and to the same extent affecting the specific gravity. The action of chlorine in removing the olefiant gas and other more dense hydrocarbons, the principal light giving materials of the coal gas, showed a per centage of these substances never exceeding 10 per cent. But not having time at the moment to guard against all sources of error in the process, laid it aside. My attention was principally directed to the simple inquiry to what extent will the illuminating power of the gas be impaired by keeping it in contact with water for noted periods. That it does deteriorate when thus kept, or when kept in contact with oil or even close vessels has been long known.

Dr. Ure tells us that gas from oil when first made and with a specific gravity of 1.054 will give the light of one candle when burned from jets consuming 200 cubic inches per hour. But keep the gas three weeks and then to get the same light from the same burner you must supply 600 cubic inches per hour. He adds that with coal gas the deterioration appears to be more rapid. For if such gas when first made will give the light of one candle by the consumption of 400 cubic inches per hour, when kept four days will require the consumption of 460 cubic inches per hour to give the same light. My first attempt to obtain some definite results began on the evening of the 8th ultimo, when I filled a large receiver from the street main and placed it on the shelf of the pneumatic trough, the next evening I filled a second one and put it alongside of the first, the following evening I filled a third receiver, and still the following evening, the 11th inst., I filled a fourth receiver. On the evening of the 12th I was thus provided with four jars of gas, one of which had been standing 24 hours or one day over the pneumatic trough, this I will call No. 1; another, No. 2, had been standing two days; No. 3 had been standing three days, and No. 4 bad been four days in contact with the water. The diminution in volume by such exposure was indicated by a receiver graduated to cubic inches into which I introduced 130 cubic inches of gas on the evening of the 8th; on the evening of the 12th this had lost about 103 cubic inches, indicating a loss of about 8 per cent. of the original bulk.

The effect produced on the illuminating power of the gas by the loss of volume became at once apparent as I proceeded to contrast the value of the flames furnished by the contents of the several receivers, 1, 2, 3, and 4. I used for this purpose the ordinary photometer arrangement, taking the relative intensity of the shadows produced, as a measure of the relative intensity of the light. The candle employed for the comparison was the patent candle already referred to, and the burner was the kind known as fish tail burner, which had been previously guaged, and known to consume a trifle more than 5 cubic feet per hour with the average maximum pressure of the gas works. I need hardly add that the burner was the same in all the trials, and occupied exactly the same position. The burner and the screen on which the shadows fell were not moved at all during the experiments. The only adjustment wanted was to bring the candle nearer to or father from the screen, and by beginning with the most luminous gas the adjustment became simply a gradual withdrawal of the candle.

The capped receiver from which the gas was passed floated freely in a large glass jar, supported in an erect position by the perpendicular sides of the jar, its own weight, with all attachments, making a difference of level between the water around it and that within equal to 34 inches, a little exceeding the ordinary evening pressure in the gas pipes. This difference of level, and consequently the pressure on the escaping gas, was kept uniform by the spontaneous sinking of the receiver as the gas was consumed, a flexible tube communicating between the stop of the receiver and the gas burner. This arrangement gave me a steady, equable flame, which continued perfectly uniform long enough to enable me, after a few trials, to note, very exactly, its true value. The results as first obtained were too startling to be at once believed, but subsequent repeated trials satisfied me that they were very close approximations to the truth. The first trial was with the gas from the street main, which I found equal to 10.71 candles. The same gas, transferred from the pipe to the capped receiver, and burned immediately, gave exactly the same power, 10:71 candles. Gas No.1 was next used, and found equal to only 3.50 candles; Gas No. 2, after standing two days, gave the light of 3.20 candles; Gas No. 3, three days old, was equal to 1.90 candles; and Gas No. 4, four days old, gave the light of 1.75 candles—these quantities representing the average of repeated trials.

It thus appears that the illuminating material of our coal gas is so rapidly abstracted by suffering it to remain in contact with water, that the same volume of gas which to-day will give me the light of nearly 11 candles by standing until to-morrow will give the light of only 3} candles, and if left standing four days will give the light of only 18 candles, while the only means left to the consumer to get the light he requires from this deteriorated gas is to burn more of it, as we have all been doing through the past winter. If we now take into account the well known fact that gas of less illuminating power has less density, and that gas of less density passes more rapidly through a given aperture than gas of greater density, we have another cause operating to increase the consumption. In Hedley's experiments the Argand burner which gave the light of 25 candles when supplied with 3 cubic feet per hour of gas from Welsh cannel coal, with a specific gravity of .737, required no less than 74 cubic feet per hour to give the same light, from the same burner, when the gas was made from the Newcastle coal and had a specific gravity of only .475.

Again, as we diminish the illuminating power of the gas we increase its heating power, and this necessarily brings with it a higher temperature given to the burners, a higher temperature given to the gas passing through them, and again an increased rapidity in the flow. It is thus manifest that the public are placed in a peculiarly unfortunate position, since all the mistakes that are likely to occur in the process of manufacture are mistakes that must inevitably increase the bills of the consumer and the profits of the manufacturer. If the workman fails to raise the heat with proper rapidity, if he overlooks a retort and allows the heat to continue a little too long, if towards the close he allows the heat to rise a little too high, the result is inevitable the product is deficient in illuminating power. Or if on any one day a little more gas is produced than is legitimately required, the surplus remains in the gasometer to vitiate the supply of to

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