ON THE MANUFACTURE OF GAS. 
133 
fuel, but also a good deal of fresh coal. By successive im- 
provements, however, in mounting and managing the re- 
torts, our gas companies have finally succeeded in effecting 
the production of their gas, by the expenditure of from 
one-third to one-fourth of the coke ; thus reserving for sale 
from two-thirds to three-fourths of the whole. The main 
source of profit to the companies at present proceeds, 
therefore, from the sale of their coke, so that they may, 
with as much propriety, be styled manufacturers of coke, as 
of gas. 
You have properly animadverted on the little novelty in 
Mr. Palmer's patent, too little indeed to resist an action at 
law : but it is surprising that a person who has been so long 
tampering with gas as Mr. Palmer, should be apparently 
ignorant of the first principles on which the illuminating 
power of carburetted hydrogen depends. This subject was 
fully investigated by the illustrious French chemist, Ber- 
thoUet, more than forty years ago. 
The good gaseous products of the decomposition of coal 
in retorts are chiefly two, viz., carburetted hydrogen (of the 
same composition as coal-mine gas) and bi-carburetted 
hydrogen, called also olefiant gas. The latter contains 
twice as much carbon as the former, to which it owes its 
rich illuminating power. Well made coal gas, from good 
Newcastle coal, contains, in its crude state, from ten to 
eighteen per cent, of this superior gas; though a good deal 
of it is abstracted and lost in some gas-works by injudicious 
wavshing ; for olefiant gas is soluble pretty largely in water. 
Berthollet demonstrated, that if pure olefiant gas be 
transmitted through an ignited tube, it is partially decom- 
posed with deposilion of charcoal, and becomes a sub- 
carburetted hydrogen gas. In this way a bright burning 
gas may be so much impoverished of carbon, as to afford 
only a blue flame. Nothing, therefore, can be imagined 
more preposterous than Mr. Palmer's project of improving 
his manufacture of gas by transmitting it through ignited 
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