745 GEOLOGY OF OHIO. 
4 
retorts are highly heated the richer hydrocarbons, if formed at all, are 
broken up in the retort, some of the carbon taking the form of pitch, 
coke or graphite, and the hydrogen with a portion of the carbon, 
escaping in a gaseous state, probably as marsh gas. It is also quite 
probable that the tendency to break up the paraffine series is much 
greater under pressure than when free to escape as soon as generated, 
or when generated free from any pressure. 
The quantity of tar to be derived from a ton of coal in gas-works 
varies largely, not only with the heats of the retorts, but much more 
with the character of coal. The Ohio coals, so far as we have been 
able to ascertain, give five to seven per cent.; best Youghiogheny, 23 
to 5 per cent., while some grades of Boghead cannel have yielded 
nearly 33 per cent. of tar, and the Leshmahago cannel, 20 to 25 per 
cent. | 
From coal tar is distilled benzole, creosote, naphtha, carbolic acid, 
anthracene, analine, alizarine, and numerous other products of great 
value in the mechanic arts and sciences. The last named compound, 
alizarine, or as it is sometimes called, artificial madder, was not known 
to be a constituent of coal tar until about 1869. At that time it would 
sell for $100 per ton. In two years time the demand had so increased 
that it was worth $2,500.00 per ton. 
In 1879 it was estimated by competent authority that the aniline 
and alizarine dyes were manufactured from coal tar to the value of 
nearly $16,000,000.00, but none of it made in this country. And even 
at this late day the gas manufacturers of Ohio are, so far as the writer 
has been able to ascertain, making little or no effort to profit by the 
experience of their European confreres. It is doubtful if more than 
$60,000 to $75,000 is obtained per annum for all the gas tar made in 
the State, while at an expenditure of not to exceed $50,000 for plant, it 
is estimated by George Shepherd Page, of New York City (probably the 
ablest authority in this country on this subject), more than twice the 
profits might be had from the tar, and that without attempting to 
manufacture any of the more costly dyes. | 
In a paper read before the American Association of Gas Engineers, 
in October, 1880, Mr. Page gives an estimate of the comparatively crude 
products that may be obtained from the tar of 265,000 tons coal. The 
quantity of coal is so nearly the estimate of the quantity used per annum 
in the gas-works of the State that it is here presented : 
