The analysis, technical valuation, purification, and use of coal gas

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CHAPTER I. Condensation of G^ 1

CHAPTER n.

Purification of Gas 11

CHAPTER ni.

Light-Measuring 41

CHAPTER IV.

Place of Testing Gas 76

CHAPTER V.

Test Candles — the Standard for Measuring Gas-light . . . .90

CHAPTER VI.

Test Burners . 106

CHAPTER Vn.

Testing Gas for Sulphur 135

CHAPTER Vin.

Testing Gas for Ammonia 162

CHAPTER IX.

Condensation by Bromine 206

CHAPTER X.

Gravimetric Method of taking Specific Gravity of Gas .... 224

IV CONTENTS.

CHAPTER XI.

PAQB

Carburetting or Naphthalising Gras 242

CHAPTER XII.

Acetylene 282

CHAPTER XIII.

Explosions of Gas. Gnawing of Gaspipes by Rats 292

CHAPTER XIV.

Pressure as related to Public Lighting 295

THE

ANALYSIS AND USE OF COAL GAS.

CHAPTER I.

CONDENSATION OP GAS.

When coal is put into retorts for distillation it contains water, and a considerable quantity of additional water is formed during distillation. This water takes up ammonia, sulphuretted hydrogen, carbonic acid, cyanogen, &c., and also a part of the volatile light-giving hydrocarbons to which coal gas owes much oiF its luminosity.

During the distillation a quantity of impure hydrocarbon oils are formed, which are well known under the name of gas tar. Both this tar and the anunoniacal liquor must be separated from gas when it leaves the hydraulic main, or the whole of the purifying and storing apparatus would become filled with them. They are removed by a process of cooling the gases and vapours, commonly known by the name of " condensation," The apparatus employed for this purpose is called a " condenser," and the forms in most general use are shown in the annexed figures.

\m fitiif

J

III "^5 s^

The condenser is essentially a quantity of iron pipes, wliich are in communication at the bottom with an iron chest-like receiver, into which the tar and ammoniacal liquor fall, and from which they run into subterranean stores, like large wells. The condenser acts by transmitting heat from the gas and vapours within to the external air or water in contact with its outer surface, and by this the gases and vapours are cooled so as to separate the one from the other. The vapours become fluids, and fall into the wells ; and the gases pass on to be purified, stored, and used. About ten feet of condenser-surface for each thousand feet of gas made per day is allowed by the best engineers, but very wide departures from this proportion are familiar to all who are acquainted with gasworks as they exist in fact.

Hitherto principles of science seem to have had but Uttle connexion with condensation ; but if the gas were reduced to the " proper temperature" before it passed on to the scrubbers or purifiers, the true object of purification has generally been considered as accomplished. An engineer has thus expressed the general

PRINCIPLES OF CONDENSATION. 3-

aim and opinion : " Still further to separate all condensable vapours before allowing the gas to pass to the purifiers, a set of condensers, or coolers, is provided, through which the gas is made to circulate until it is reduced to a temperature bearing some approximation to the surrounding atmosphere." There could be no more mistaken practice than the one commonly adopted, for it is in the power of most engineers to make a coniuderable difierence in the illuminating power of all the gas they manufacture, by the adoption of a better mode of condensation. The increased illuminating power obtained by a superior method of condensation is obtained ahnost without cost for material, whereas, when gas is improved by the use of cannel coal, the cost for material is considerable. If a quantity of the lighter hydrocarbons are withdrawn from tar and sold with gas, the tar will probably become of less value, and the difference between its present value and its value in the future (if reduced) might be called the cost of the material for producing the extra light; but, even so, the extra light would be produced far more cheaply than by other means at the command of a gas manufacturer.

So few people are conversant with the principles involved in this question, that I propose to consider some of its details, in order to make the matter clearer. The proper object of condensation is the removal from gas of substances produced in the distillation, which, for some reason, are not useful for the purpose of illumination, and the retention in the gas of all the sub^ stances which are useful as illuminants and can be distributed with the gas. Water and most of the compounds which the water holds in solution are useless, and cannot be distributed with the gas. These, therefore,

b2

NAPHTHA IN GAS.

should be removed. The heaviest hydrocarbons (tar) are useful as illuminants, but cannot be distributed with the gas, and therefore they should be removed. But the gases and the lighter hydrocarbon vapours are useful, and can be distributed ; and therefore no more of these should be removed than is absolutely necessary to effect a proper removal of the compounds which must be removed, because they are useless as light-givers, or cannot be distributed. Of all substances, the most useful as light-givers, when burnt with gas, are the vapours of hydrocarbons, and therefore every pains should be taken to keep in the gas the largest possible quantity of these vapours. All the light hydrocarbons, known as " coal naphtha," have been obtained by the distillation of gas tar, and consequently have been separated from gas by the process of condensation now used in our gasworks. If gas be passed over this naphtha, it gradually disappears, and the gas which passes over the naphtha acquires considerably greater illuminating power than it possessed before its passage over the naphtha. This simple experiment shows, first, the illuminating value of the naphtha which was removed from the gas during the manufacturing process, and, secondly, the power of the gas to take up and transport so much of the naphtha as to acquire considerably greater illuminating value, when the naphtha is presented to it alone, without the presence of any other substance which acts antagonistically to the gas. Some published experiments made in the City Laboratory show that four grains of naphtha added to a cubic foot of common London gas increase its illuminating power 25 per cent., and 10-77 grains added to a cubic foot of the same gas increase its illuminating power 77 per cent., so that a gas manufacturer's aim should be to keep

HEATT OILS DC GAS. 5

in his gas the largest portion of this vapour which his coal will furnish, and he can distribute. I never yet saw common gas which would not take up, and cany during its distribution, four or more grains per foot of suitable hydrocarbon vapour. At present most manufacturers of gas take the best means with which we are acquainted for removing hydrocarbon vapours from gas. They cool their gas and hydrocarbon vapours down to 60"* or 70"* F. (and in some cases lower), as quickly as they can, and the form of condenser which will do this most quickly and certainly is the one generally preferred. No suspicion seems to cross their minds that they are enabling the tar {i.e. the heavier oils) to dissolve out from the gas, and carry down with it the vapours of light hydrocarbons which they ought to retain in their gas with the utmost sedulity. To understand this it is necessary to understand something of the nature and properties of the complex substance called gas tar. The following Table does not profess to be complete, but it will suffice to give as much information as is necessary to enable an attentive person to understand the subject of " condensation," though he may have no chemical knowledge. It is arranged according to the boiling-points of the substances contained in it.

This Table includes all the heavy hydrocarbons which form tar, as well as the lighter and more volatile ones, such as benzole, and it may be objected by some persons that heavy oils cannot be carried by gas. This is a mistake. I have obtained from the gas supplied to my house a quantity of oil so heavy, that is, of such high boiling-point, that a Florence flask in which it was distilled, softened and partially lost its shape before the oil could be driven over. These heavy oils were obtained by passing the gas over carefully fractionated

6 SEPAKATION OF LIGHT AND HEA^T OILS.

pure light coal oils. The gas deposited a portion of its heavy oil, and took up the light instead. I have likewise fractionated oils obtained from the syphon wells of street mains, and have found them to contain the whole aeries of hydrocarbons, up to the very heavy ones I have mentioned above. I have likewise passed gas at common atmospheric temperatures over hydrocarbon oils boilmg from 220° F. to 280^ F., and the wMe was taken up ; so that, in any inquiry as to the power of gas to take up and carry the hydrocarbons which form tar, we must not confine our^ view merely to benzole, and other hydrocarbons of still lower boiling-point, but must extend it at least to those which boil as high as 400° F.

Mere inspection of this Table will show the most unskilled person that benzole will boil and pass away as vapour at 36° F. below the boiling-point of water, whereas another neutral fluid hydrocarbon, caj)royle, requires to be heated to more than 183° F. above the boiling-point of water before it will boil and pass away in vapour like the benzole. It seems obvious then that, if we wish to keep the vapour of benzole in gas, and to separate the caproyle from it, we ought to keep all the substances produced in distillation at a temperature slightly above 176^ F. and below 395° F. It seems as obvious that if the whole products of the distillation ^are cooled down quickly to 60° F. or 70° F., that all, or nearly all, the substances condensable at that temperature will be condensed and removed from the gas as fluids or solids, according to their habitudes. Mere inspection of the Table would lead to this ; but it would iiot lead unskilled persons further. Those acquainted with the subject are aware that it is capable of leading „much further, and to very useful conclusions. It is

^"^eut^cific gravity.

H

Hexelene

Heptylene .' .714

Benzole .

Butyl .

Toluole .

Cnmole

Amyle

Cyniole

Caproyle Naphthalin

•882 •705

•872

•774

•96

•853

•921

1^028

•756

1^048

1-081 raraiia2)hth:

]Vlotaiia])hth)

Chrysene

Pyreiie

Paraffin

Specific gravity of vapour.

3-397

2-698 4-070 3182

3-666 4-992 4151

5^897 4528

4-519 514 6-78

*:w^^^'^'^^^*" r*^ CAemW Society, 2nd series, vol. iv.,

[To face page 6.

p. 3 JG.

J warren's condenser.

known that mere distillation is incapable of separating the various classes of hydrocarbons from each other; that those of low boiling-points carry over with them portions of others of high boiling-points, while the latter retain some of the former, although they have been heated considerably above the boiling-points of the lighter compounds. So much is this the case, that I never 3ret examined a sample of commercial benzole ■yvithout obtaining naphthalin from it, though the latter boils at 410^ F., and the former at 176° F. ; and I have no recollection of meeting with a sample free from some portions of the less volatile fluids, caproyle, c3^mole, &c. These substances dissolve in, or unite chemically with, each other (I think there is strong evidence that the latter is the fact), and we must resort to a carefully conducted artificial process to separate them. Mr. Warren's condenser will explain how this is best accomplished. That gentleman uses an ordinary condensing coil of pipe, but instead of keeping it cool he keeps it hot, and instead of sending the vapours into the top, and allowing the condensed fluids to descend, he sends them into the bottom of the coil and compels them to ascend. The coil is heated to the boiling-point of the volatile substance which he wishes to separate, and the mixed vapour from the retort is sent into the lower part of the coil. In its passage upwards the vapour is distilled, the more volatile compound passes on to be condensed into fluid in the ordinary manner, and the less volatile ones condense in the heated pipe and fall back into the retort. This beautiful arrangement points out what ought to be done in condensing gas. The hydraulic main ought to be kept at a proper temperature, and to be prolonged sufficiently to allow the less volatile bodies to condense and pass away to the tar

8 INFLUENCE OF HEAVY OILS ON UGHT ONES.

well) and the more volatile to go forward with the gas ; or, what is much better, a special apparatus, kept at a regulated temperature, should be interposed between the hydraulic main (in this case kept hot, of course) and the purifying apparatus, in which the gas and lighter hydrocarbons might be separated from the heavier bodies, and so a larger proportion of hydrocarbon vapour might be distributed with the gas; in other words, the gas might be made more iUuminating. • If thus separated, there would be no difficulty in distributing all the light hydrocarbon vapour which the tar would give up, as may be proved by the well-known process of pouring naphtha into the mams, which the gas picks up on its passage and carries to the consumers. Gas, at common temperatures, can take up and carry a considerable quantity of the vapour of the lighter hydrocarbons, if they he hrowghJt into contact vnth it after liaving been separated from the heavy ones ; but the power of the heavy to carry down the light is greater than that of gas to carry them on, and hence all fall together in the present system of condensation, to the great detriment of the gas. The loss of light which gas sujffers upon being passed through cold heavy oil, and the inability of the same oil when heated to act upon it, will illustrate this. I have passed gas through heated heavy coal oil boiling about 400"* F., and have foxmd its illuminating power identical with its illuminating power before it was passed through the oils. It gave up nothing to them, and it took up nothing from them. I have also passed gas through the same kind of oil at ordinary temperatures, and have had its illuminating power reduced to less than 1 candle for a consumption of 5 ft. an hour, whereas before passing the gas through the oil it had an illuminating power of

UGHT OILS UPHOLD NAPHTHALIN. 9

13 candles. The cold oil had dissolved out of the gas nearly all its illuminating matter. In the present method of condensation this is imitated in a great measure. All the oils, the water, and the gas are cooled together, and thus an opportunity is afforded to the heavy oils to dissolve out the light ones from the gas, whereas the heavy oils should have been condensed, first, at such a temperature that they could not damage the gas, and then the gas and the lighter vapours should have been cooled to the temperature proper for purification.

This method of condensation would probably tend to lessen the deposition of naphthalin in gas mains, which now causes so much trouble. It is well known that naphtha poured into mains obstructed by naphthalin will dissolve it, and that deposition cannot occur at ordinary temperatures in the presence of a considerable quantity of the vapour of the lighter hydrocarbons. It seems probable, therefore, that the presence in gas of as much hydrocarbon vapour as the suggested process would keep in it would enable it to uphold its naphthalin in a state of vapour by diminishing the tendency of the naphthalin to crystallise. If it will accomplish this, it will be a great boon to those engineers who use Newcastle coal and very high heats. I should expect it to contribute to this end in another way. The heavier compounds which form tar have a strong affinity for naphthalin at high temperatures, and as they condense are apt to carry down the naphthalin with them, I should expect, therefore, that by the fractional condensation which I have suggested so much naphthalin would be removed from gas by the heavier compounds which would separate in the "hot condenser," that the vapours of the lighter oils would be able to uphold

10 ORDLVARY CONDENSATION.

the remainder, and thus stoppage of mains would become a very rare thing, if not a thing unknown. It is impossible for me here to state at length the reasons for this expectation. It must suffice to say that a large and long experience leads me to it, and I shall be much surprised if it do not prove in some measure correct. After gas had undergone the removal from it of all which the hot condenser could remove, it would pass through the ordinary condenser as at present; but it would be wise to keep its temperature as high as is consistent with efficient purification. Now, gas is generally over-condensed in order that it may not measxire more at the station-meter than can be avoided, in other words, may not make the leakage appear more than it appears at present. This is unwise, and almost makes one wish that all gas companies were like one or two of the largest ones, without station-meters. If gas be measured at, say, 90° F., and then cooled in the storing and distributing apparatus to, say, GO"" F., every one knows that it becomes diminished in bulk by the cooling* But this makes no difference whatever in the rental received for what passes the consumers' meters. This is the same whatever be the temperature at which the gas passes through the station-meter, and a board of directors would manifest signal ignorance of their business, if they found fault with an engineer for doing that which really improved their gas without cost. The apparent though not real increase in their leakage ought not to be considered. I dare say there are boards capable of complaining of such a procedure, instead of commending it as they ought to do ; but when they foimd that the money received for gas bore the same relation to a ton of coals as ever, I cannot think any men would be unreasonable enough to adhere to their objection.

CHAPTER 11.

PURIFICATION OF GAS.

This subject is best treated historically. It may be divided into five periods. The first period, extending from the time when gas began to be used as an illuminating agent to 1808, when Winsor first used what he called lime-water for purifying from sulphuretted hydrogen. The second, extending from 1808 to 1815, when Clegg introduced machinery to stir up the mixture of lime and water which was then used in purification ; when, in fact, the term purification became, for the first time, applicable. The third, from 1815 to 1817, when Phillips introduced the practical improvement commonly called dry-lime purification. The fourth, from 1817 to 1849, when Hills introduced his revivified oxide of iron. The fifth, from 1849 to 1860, when I introduced the use of heated lime, to render all sulphur compounds removable, and removed them by lime or alkalis. During the first period there was hardly any attempt at purification until Winsor tried his process. He washed the smoke, as he called it, with water before it was burned for the purpose of illumination. In the year 1806, a person named Heard, who.

12 heakd's and winsor's purification.

it is stated, had been an assistant to Winsor, was very near introducing an excellent system of purification. When his gas was produced, he tried to purify it by passing it over lime ; but whether the lime was slaked or not I am not sure. Unslaked lime would be nearly useless ; but even if he were so unchemical as to use his lime unslaked, the water introduced with the gas would slake it partially, so as to render it useful in a measure. The mistake he made was in passing the gas over and not through the lime ; for although when passed over it the particles of gas which happened to come in contact with the lime would be purified, yet the major part would pass away from the purifying vessel without coming into contact with the lime. This rendered the process practically useless for removing the sulphiu^etted hydrogen. In addition to lime, he used the fixed alkalis, alkaline earths, and also the oxides of iron, manganese, zinc, copper, lead, &c. If he had passed the gas through the purifying material, he would have done] at that early period of the history of gas-lighting nearly all which was done up to 1860.

In 1808, Winsor made a great improvement, for he passed the foul gas through a vessel which was perforated with small holes, and filled with lime-water or cream of lime, which he said withdrew the sulphur and other offensive substances. He also proposed to put lime into his retort, but he made the mistake of placing it at the bottom instead of at the top of his charge, a mistake which it seems difficult at this day to account for. There is no question, however, that his experiments brought the impurities in the gas better into contact with the milk of lime than they had been brought before, and consequently what he did was a great step in the history of purification. In the year 1808, Henry

CLEGG's IMPRROVEMENTS. 13

and Clegg put up still better purifying apparatus for using milk of lime; and Taylor patented his mode of purifying gas made from bones and animal matter (I cannot see why he should not also have included that naade from coal) from sulphuretted hydrogen by lime and water, and then from ammonia by dilute sulphuric or hydrochloric acid.

In 1815, Clegg's practical skill improved the purification greatly. He introduced apparatus to stir up the milk of lime, instead of allowing the lime to settle at the bottom of the vessel as it had done up to that time. By stirring up the lime the gas was brought more effectually into contact with it, and consequently was better purified than it had been before. In fact, he really effected a very complete purification of gas from sulphuretted hydrogen and carbonic acid ; and if it had not been for one serious drawback, the purification by wet lime, well agitated, would have remained until this day the best process for removing the particular compounds from gas which it is adapted to remove. This drawback was the large amount of refuse left by the process, and the pressure it threw upon the retorts. The latter could now be overcome by using an exhauster ; but the former was invincible, and sufficed to cause rejection of the process. The refuse was icalled " Blue Billy " by the workmen, and Blue Billy can hardly be mentioned in the presence of old gas engineers without awaking recollections of troubles and prosecutions which they have long since consigned to forgetfulness.

We have lately heard much about ammonia as an allpowerful substance for removing sulphur compounds from gas, and more than one person has shown a disposition to claim its use as an original discovery. It will

14 Phillips's dry lime purification.

surprise many to be told that so long ago as 1817 a person named Wilson actually suggested and patented this very substance as a purifying agent. He tells us that he set free ammoniacal gas from gas liquor by means of lime, and mixed the ammoniacal gas so freed with coal gas between the retorts and the gasholder, and then caused the mixed gasea to pass through a perforated plate placed under the surface of water ; that is, he made a solution of ammonia, and washed the gas therein, to remove sulphuretted hydrogen and carbonic acid, together with cyanogen and certain other compounds, of which, I dare say, he knew nothing, but which would be removed notwithstanding.

A great practical advance in purification was made in this year by Phillips, of Exeter, who introduced what is commonly known by the name of " dry lime purification," but for which improvement the use of gas must have been greatly restricted. We are indebted to this improvement for the non-production of that offensive substance called " Blue Billy." Phillips freed gasworks from this nuisance by lessening the amount of water employed with lime when it was used as cream in wet-lime purifiers. He slaked the lime with water, and afterwards added to it just so much more water as made it moist enough to form a ball in the hand upon gentle pressure, and in this state it was used upon sieves or trays, and the gas passed through it. He thus describes his invention : "I take any quantity of well-burnt lime, and pour water on it till it falls to powder. I then mix it with a further quantity of water, in order to bring it into such a state that the particles of lime may adhere slightly to each other, but not to such a degree as to prevent the free passage of the air between. This mixture must be placed six inches deep, more or less, on

movable perforated shelves, in a vessel the top of which is guarded by a water-joint, and underneath is a pipe, to allow the passage of the gas that way, so as that the gas may pass from the bottom of the vessel to the top through the perforated shelves and lime mixture, or from the top to the bottom, as may be found most convenient, the purification being effected by the gas being caused to pass through the layers of lime mixture. But where the quantity of gas to be purified is very large I arrange a set of these vessels, consisting of five, or nine, or more, according to the size of the gasworks, each vessel containing one or more shelves."

This process was soon adopted by gas companies in all the large towns, and it remains to this day the process by which nearly all the gas of the world is* purified, except in London and a few of the very largest towns and cities. Phillips patented his discovery in order to obtain remuneration, but the invention is said to have cost the unfortunate patentee his life. He thought, and thought reasonably, that he had a right to be paid for his invention by those who availed themselves of it to save expense and avoid prosecution for nuisance, and consequently he proposed that all companies which used his process should pay him a royalty for its use. But the companies, in a spirit of cupidity which will ever disgrace them, used the power of the purse to put down and defraud a poor but deserving man, whose invention was rendering them a great and essential service. I am informed that they used the process, then combined together and subscribed large sums of money to resist PhilHps's claim. As soon as he attempted to enforce the claim by law, he was met by their formidable combination, and, worn out by the harass of legal proceedings, he died. His widow then

16 palmer's purification.

abandoned the proceedings, and accepted any small sum which the gas companies were willing to give her for doing so. These facts are not within my own knowledge. My informant was one of those who, on behalf of the gas company in which he was a principal shareholder and director, entered into the unjust combination with the other companies.

It was not till 1849 that Hills introduced his process of using revivified oxide of iron for removing sulphu. retted hydrogen from gas, but in 1818 a person named Palmer was not far from it. He proposed to purify gas by passing it through red-hot iron. This process could not be made effectual, as a large quantity of the light-giving matter of the gas was destroyed by its passage through the red-hot iron, while but little purification was effected. I mention him because he seems almost to have got at the notion of revivification of oxide of iron. He tells us that when one of his purifiers is thrown out of connexion, it does not need to have its contents removed, but they can be revived by the action of the air.

He describes his process thus: "The purifier is to be kept moderately red-hot, and is to be filled with fragments or refuse clippings of sheet iron, or any oxide of iron, at a minimum of oxidation, such as common clay or argillaceous iron ore, or finery cinders, or black oxide of iron ; and when so filled and treated, the gas must pass through it, which will effect a partial decomposition of the sulphuretted hydrogen, and will be completely effected by passing into a box or cistern of cold water. When one of the purifiers is thrown out of action it need not have its contents removed^ but its doors must he left open to expose it to the action of the atmosphere^ and as it is still kept red-hot^ it willj before the second puri-

CR0LL*8 PROCESS. 17

fier becomes saturated^ he again competent to purify the gas^ If Palmer had changed the method of his purification to a cold process instead of a hot one, and had exposed his foul . material to the air, he would have anticipated Hills ; for having got so far, the phenomena with which he would have become familiar must have led him the rest of the way to purification by revivified oxide of iron.