118 



UNDULATORY FOUCES LIGHT. 



[WASTE I'UODUCTS. 



q"it the retort, they consist of aqueous vapour, Ur, 

 oletiant gas, anil otlu-r rich hydro-carbons, light carl>u- 

 -. hydrogen, hydrogen, carbonic acid, carlxmic 

 oxide, sulphuretted hydrogen, sulphuret of carbon, 

 cyanogen, and ammonia. Only a few of these are 

 required for illuminating purposes, and the rest must be 

 got rid of. Foremost in the order of purification is that 

 which takes place in the hydraulic main. There the 

 most coudensible of the ompyreumatic vapours are de- 

 posited, and they run away into the neighbouring tank 

 as a most fetid' mixture of tar and watery matters. 

 N<-\t to this is the condenser an apparatus which ex- 

 poses the gas to a large extent of cooling surface. We 

 have already described the form of the apparatus, and 

 aid that it causes the condensation of the liquifiable 

 matters contained in the gas. It precipitates tar, water, 

 and ammonia, in combination with sulphuretted hydro- 

 gen, carbonic acid, and cyanogen. In some cases, the 

 gas is made to pass through a vessel containing pieces of 

 coke, over which a stream of water is constantly running. 

 The gas enters at the bottom of the vessel, and, having 

 made its way between the fissures of the coke, it escapes 

 at tlio top. A stream of water runs over the coke in an 

 opposite direction ; and thus the gas is, as it were, 

 washed and scrubbed by the two materials with which it 

 is brought into contact. This apparatus is, therefore, 

 very appropriately named a scrubber. The only impu- 

 rities then left in the gas are ammonia, carbonic acid, 

 sulphuretted hydrogen, cyanogen, and bisnlphuret of 

 carbon. These can only be removed by the aid of 

 chemical absorbents ; and the gas is, therefore, made to 

 pass through a set of vessels which are named par excel- 

 lence, the purifiers. These contain milk of lime, or lime 

 that has been recently slaked. In the former case it is 

 named a wet-lime purifier, and in the latter a dry. In 

 both cases the gas enters at the bottom of the vessel, 

 and it is either distributed in a stream of small bubbles 

 through the liquid, or else it pursues its way between the 

 moist particles of the recently slaked lime. By this 

 contrivance, carbonic acid, cyanogen, and sulphuretted 

 h yi Irogen are extracted from the gas ; these combine 

 with toe lime, and produce a most unpleasant-smelling 

 Compound, which is technically termed bhte-lrilly. In 

 consequence of the loss of ammonia by this process of 

 purifying, and the disgusting nature of the refuse mate- 

 rials, a number of patents have been taken out at various 

 times for the purification of coal gas by other means 

 than that of lime alone. The oxides of iron, in various 

 conditions, have been patented by Messrs. Croll, Hills, 

 Laming, and Lowe ; the common salts of lead have been 

 patented by Mr. Lowe and Mr. Losh; oxy-chloride of 

 antimony, by Mr. Kirkham ; sulphate of iron, with com- 

 mon salt and charcoal, by Mr. Cormack ; sulphate of 

 lime and magnesia, by Mr. Hills; superphosphate of 

 lime, by Mr. Johnson ; muriate of lime, by Mr. Laniint; ; 

 muriate of manganese, by Mr. Croll; and clay, by Mr. 

 Bowditch.* Indeed, it would appear as if all the refuse 

 matters of the arts had been successively tried and 

 patented, in the hope of their becoming a means of 

 extracting the impurities from coal gas. In most cases 

 these substances merely absorb ammonia, and in a few 

 instances they take up sulphuretted hydrogen also. 

 Quitting tho pnriliers, which are charged with one or 

 of the preceding compounds, the gas enters the 

 gasometer, and is in the condition in which it is to be 

 supplied to the public. 



The products of these operations are more or less 

 valuable in every stage of the process. The coke which 

 is drawn from the retort after the extraction of the gas, 

 meets with a ready sale; the ammoniacal li<|imr which 

 floats UTKin the tar in the tanks of the condenser and 

 lr. 'Inuilic main, contains enough ammonia to make about 

 sixteen ounce* of sulphate, t .. I . - .1 nd-a-half of carbonate, 

 or eleven-and-a-half of muriate, from each impel i.-il 

 gallon; and as each ton of Newcastle coals produces 

 from ten to twelve gallons of thin liquor, there is a large 

 !M->uiit of valuable matter generated in tho process. 



Mr. \jn\\r rmplDTn unlphitf of eoppr and ictutr of lead fur >ucb 

 pnrpoMi, in tu* punflen at Bu Laura u! Uw Muwnwn. JUtlor. 



The tar also is made to give up its wealth l.y tho all- 

 powerful aid of chemistry. As it leaves the manu- 

 factory, it is a dark-coloured, heavy liquid, of a most 

 unpleasant odour: but, by distillation in rude in>n 

 boilers, it furnishes naphtha for lamps, dead -oil or creosote 

 for railway timbers, and pitch or asphaltum for a variety 

 <>f purposes. When the richer varieties of cannel coal 

 have been used for the generation of gas, tho tar also 

 contains paraffine, which has already been described ; and 

 it likewise yields, by distillation, an oil which is largely 

 employed for lubricating machinery. Within the last 

 few years a number of patents have been taken out for 

 the management of coal-tar; but as yet we have only 

 begun to nave an insight into the nature of tho many 

 valuable compounds that are locked up in it. Neverthe- 

 less, three classes of bodies have already been discovered 

 in coal-tar; namely, neutral principles, acid substances, 

 and alkaline matters. Among the first are benzole 

 (C"H'>, toluole (C"H S ), cumole (U"H"), cymole (C"ll";, 

 naphthaline (C""J1"), paranaphthaline (C^H"), pyrene 

 (C'W), chrysene (C"H), paraffino (C M H"), and various 

 liquid hydro-carbons, which nave not yet been isolated 

 Among the acid substances, the most important is the 

 acid of creosote, or carbolic acid (C"H*O') ; and of the 

 alkaline matters there are pyridine (C l H'N), pycoline 

 (C"H'N), and its homologue, aniline (C"H 7 N), lutidiiiu 

 (C"H'N), leucoline (C"H 7 N), a new base (C U H"N), 

 and parvoline (C"H U N) : in addition to which, there are, 

 in all probability, other compounds which are isomeric 

 with tho preceding. Now the great and interesting fact 

 which has been developed by the study of these com- 

 pounds is, that they all contain but one element of 

 nitrogen, and that, with one or two exceptions, they rise 

 by regular gradations of two of carbon and two of hydro- 

 gen : first wo have 10 + 5, then 12 + 7, then 14 + 9, and 

 so on. Besides which they are all isomeric, or have 

 exactly the same composition with another series of 

 bases called the aniline series. To the chemist these 

 facts are of the greatest importance, not merely because 

 of their individual interest, but because of their influence 

 on the doctrines of science. At one time it was thought 

 that whenever two things differed in their chemical and 

 physical properties, they must be different also in their 

 composition ; and when Professor Faraday showed that 

 one of the constituents of the fluid obtained by the con- 

 densation of oil gas, was identic!, in its chemical com- 

 position, with another body (olefiant gas), notwithstand- 

 ing that it differed from it in all its physical properties, 

 chemists were hardly able to comprehend it; but ere 

 long the fact was recognised as one of the most conimnn 

 occurrences in tho whole range of chemistry. And thus 

 an examination of the most insignificant of materials, 

 will' of ten furnish results that not only affect the ancient 

 land-marks of science, but also open up a new way to 

 the practice of industry and the acquirement of wealth. 

 Who, for example, could have supposed that so dis- 

 gusting a liquid as coal-tar a liquid which, a few years 

 . the manufacturers of gas knew not how to dispose 

 of would, through the golden key of chemistry, bo 

 made the means of changing the aspect of chemical 

 science, and of opening up new and profitable branches 

 of industry ? Take the crude tar, and submit it to dis- 

 tillation at a low temperature the temperature of 

 boiling-water : it yields a light volatile oil, which is com- 

 monly called naphtha. This consists, in great part, of a 

 valuable ethereal liquid, which we have already described 

 under the name of benzole a liquid which may be used 

 for burning in lamps, for dissolving resins, and for manu- 

 facturing a rich perfume (uitro-benzole), which has the 

 delicious odour of the essential oil of bitter ahn< 

 By continuing the distillation at a somewhat higher 

 temperature, there passes over an oil which is heavier 

 than water. This is called dead-oil ; it contains the 

 naphthaline, paraffine, creosote, and various liquid hy- 

 dro-carbons, which have not been sufficiently well studied, 

 but which perhaps contain mines of chemical Health. 

 Tho dead-oil is largely employed for the preservation 

 of timber, and for lubricating machinery : mid lastly, 

 that which remains in the still ia asphalt or pitch. As 



