176 



NA TURE 



[June 21, 1894 



candles ; and in order to ensure this over so enormous j 

 an area, the gas must be sent from the works test- 

 ing up to from 165 to 17 candles. With seaborne 

 Durham coals of the character most largely used in the 

 metropolis for gas-making, the illuminating value of the 

 gas will be about fifteen candles, and the gas manager 

 has to enrich the gas by from 1 1 to 2 candles before he 

 can with safety send it out for distribution. This enrich- 

 ment is done in several ways : (a; by the admixture of a 

 certain percentage of cannel coal with the original gas 

 coal ; (b) by carburetting the coal-gas with the vapours 

 of volatile hydrocarbons ; {c) by mixing the gas with 

 carburetted water-gas ; {d) by admixture with rich 

 oil -gas. 



Up to four years ago the admixture of a certain per- 

 centage of cannel coal with the Durham coal was the 

 only method of enrichment employed by the metropo- 

 litan companies, and was perfectly satisfactory, as the 

 coal being mixed, the gases came off together under the 

 same conditions in the retorts, and a uniform gas was 

 the result. During the past few years, however, the 

 increase in price of cannel has forced the gas companies 

 to find some other process which should take its place, 

 and the Gas Light and Coke Company tried experiments 

 which led to their largely adopting carburetted water-gas 

 for this purpose. 



When steam acts upon carbon at a high temperature, 

 the resulting action may be looked upon as giving a 

 mixture of equal volumes of hydrogen and carbon mon- 

 oxide, both ol which are inflammable but n'in-kiminous 

 gases. The water-gas is then carburetted, i.e. rendered 

 luminous by passing it through chambers in which 

 oils are decomposed by heat, and the mixture of oil-gas 

 diluted with water-gas is made of such " richness" as to 

 give an illuminating value of 24 or 25 candle-^, and this, 

 mixed with the poor coal-gas, brings up its illuminating 

 value to the required limit. During the winter months 

 the gas supplied by the Gas Light and Coke Company 

 has mos: ly contained about 10 per cent, of the carburetted 

 water-gas. 



This form of enrichment has several serious draw- 

 backs : it increases the percentage of the highly- 

 poisonous carbon monoxide in the gas, and so makes 

 leakage more dangerous, whilst carburetted water-gas 

 burns with a short but very brilliant flame, far shorter 

 than coal-gas, a 22 candle water-gas flame burning from 

 a London argand at the rate of 5 cubic feet an hour, 

 with a flame only 2* inches in height ; whilst a i6-candle 

 flame of the gas supplied up to three years ago gave a 

 flame three inches in height ; and the gas now supplied 

 and enriched with the carburetted water-gas only gives 

 a flame 2=6 inches in height, in order to emit a light of 

 16 candles. 



When a householder lights his gas-burners, he in- 

 variably turns on the gas until he gets the largest possible 

 flane without roaring or smoking, and from the alteration 

 in the composition of the gas which has taken place, this 

 means using far larger quantities of gas than heretofore, 

 so that although an increase in illuminating [)ower is ob- 

 tained, a substantial increase in the quarter's gas bill is 

 also found. 



Another objection to this form of enrichment applies 

 even still more to the admixture of rich oi l-gas with the poor 

 coal-gas, and is that although gases of different gravities 

 mix perfectly well in small vessels, yet when you come to 

 deil with the huge gas-holders used in the modern gas 

 works, stratification of the gas takes place, and even if the 

 enriching gas be mixed with the ordinary gas in the 

 foul mams, so that they may pass through the scrubbers 

 and purifiers together, uniformity in illuminating power 

 is never obtained, and with the London coal gas 

 variations of from 16 to 18 candles in value are found at 

 the testing stations. 



A burner which is giving its best duty with a 16 candle 



NO. 1286, VOL. 50] 



gas, will be very apt to smoke when burning a gas of 

 higher quality, and under these conditions the products 

 of combustion become more injurious to health from the 

 presence in them of a larger proportion of the products 

 evolved during incomplete combustion. 



Enriching gas by the vapours of volatile hydrocarbons 

 enables the manager to bring his gas up to the legal re- 

 quirements as regards the illuminating value at the test- 

 ing stations, which are mostly fixed where the great 

 trunk mains deliver the gas to the districts to be supplied, 

 and it is only under exceptional circumstances that the 

 illuminating value of the gas is ever found to be below 

 the required limit at these points The consumers, how- 

 ever, reap but little benefit from it, as the loss of 

 illuminating value during distribution is very great where 

 this method of enrichment is employed. 



No matter how enriched, change of temperature, and 

 other troubles incidental to distribution generally reduce 

 the illuminating power of the gas to a considerable 

 extent before it reaches the consumers' burners, so that 

 its actual value is far more often fifteen candles, although 

 it may have been tested over sixteen at the station. 



In the big mains the gas iscontinually flowing at a fairly 

 steady rate, and is neither exposed to any great alteration 

 in temperature, nor from the size of the mains to any very 

 great amount of " skin friction," i c. tubbing of the gases 

 against the sides of the pipes ; but as soon as distribu- 

 tion commences, both these factors come into play, and 

 as some of the chief illuminanls of the gas are v.ipours 

 and not permanent gases, lowering of temperature causes 

 condensation of some of them, whilst the power which 

 friction against the sides of the main service pipes, 

 coated with deposited hydrocarbons, has of withdrawing 

 the illuminants from the gas, still further decreases its 

 light-giving value, and anywhere near the dead end of 

 a service, stagnation of the gas during a l.iige portion of 

 the twenty-four hours when gas is not being consumed, 

 adds still further to the trouble, so that even at the testing 

 stations, the influence of the small consumption of gas 

 on Sundays, and consequent stoppage in the manufacture 

 on that day, can be traced in the illuminating value found 

 on Monday morning. 



Coal-gas, as made from Durham coal at the tempera- 

 ture employed in the Metropolitan Gas Works, has an 

 illuminating value of about fifteen candles, and the en- 

 richment of this gas up to the required value costs far 

 more/'o rata than the amount of light obtained from 

 the unenrichedgas. 



This cost has entirely to be borne by the consumers, 

 and the whole practical question to be decided resolves 

 itself into — " Is the game worth the extra candle and a 

 half.^" 



If coal-gas were used for illuminating purposes only, 

 the consumer would be a considerable gainer by having 

 the unenriched gas supplied at a lower price ; and when we 

 consider the amount of gas used as a fuel, and that the 

 quantity so employed is daily increasing, the coU of 

 the enriched gas becomes of the greatest importance. 



The value of one candle in illuminating power in the 

 gas supplied in London at \\d. per candle is ^180,000, 

 and if this calculation be correct, consumers in the 

 metropolis would be saved about /270000 a year by using 

 unenriched coal gas, and probably not one of them would 

 notice the slightest difference in the light emitted by the 

 gas in the burners ordinarily in use. 



In the regenerative burner the increase in illuminating 

 value IS almost entirely due to the rise in temperature 

 causing methane, which forms about 34 per cent, of the 

 coal-gas by volume to become a very valuable illuminant, 

 and as there is just as much or more methane in the un- 

 enriched gas, it is manifest that this increase will still 

 I be found. 



I In the incandescent burner the coal-gas is burnt in an 

 atmospheric burner, and the non-luminous flame is made 



