PETROL 291 



with additional hydrogen. They are represented by the formulae 

 C 6 H 12 , C 7 H 14 , C 8 H 16 , etc., and their boiling points range from 

 about 69 C. to near 250 C. Beside the naphthenes Russian 

 petroleum is believed to contain small quantities of benzene and 

 toluene. 



The " cracking " of petroleum for the purpose of producing a 

 very volatile or gaseous mixture of hydrocarbons, which when 

 burnt give a luminous flame, has for many years been practised, 

 at first especially in the United States, as an auxiliary to the 

 manufacture of common coal-gas. 



The gas with which towns are supplied now consists to a large 

 extent of a mixture containing gas distilled from coal by heating 

 it in retorts, together with what is known as " water-gas." The 

 latter is a mixture of carbonic oxide and hydrogen formed by 

 passing steam through masses of red-hot coke, the temperature 

 being maintained by substituting air for steam when the mass 

 has cooled below a certain point. The introduction of air gives 

 rise to carbonic oxide which remains mixed with the nitrogen of 

 the air. As all these gases, carbonic oxide, hydrogen, and 

 nitrogen together, yield a mixture which burns with a non- 

 luminous flame a small quantity of petroleum is injected which 

 being " cracked," as already explained, by the heat furnishes the 

 light-giving ingredient required. Large quantities of petroleum 

 are consumed in this way. 



Fig. 101 facing page 300 gives a view of the carburetted 

 water-gas plant on the works of the " Gas Light and Coke 

 Company " in London. 



In the year 1911 the amount of oil used by this Company for 

 carburetting the water-gas amounted to 13,401,101 gallons. As 

 it seems probable that the present high price of coal will be 

 maintained the consumption of petroleum in gas-making will 

 doubtless continue to increase. 



At this point a glance may be taken at the following table 

 which displays an estimate of the output of crude petroleum 

 over the whole world. From this it appears that the largest 

 amount by far comes from the United States, while Russia 

 follows with a yield of less than one-third of the American. In 

 the next few years this proportion will probably be disturbed to 

 some extent. 



