50 REPORT—1857. 
On some ane Results attending the Decomposition of Bituminous Coals 
y Heat. By Dr. A. A. Haves, United States. 
When bituminous coal is exposed in proper vessels to a gradually increasing tem- 
perature, at a certain point decomposition commences and continues, while heavy 
hydrocarbon vapours, mixed with the vapours of water and salts of ammonia, escape, 
and may be condensed. 
The proportion of permanent gases formed is small in comparison with the weight 
of the liquids produced, when the decomposition of the coal is carefully regulated. 
In the ordinary rapid breaking up of the composition of coal by heat suddenly 
applied in the manufacture of illuminating gas, the proportion of permanent gases is 
increased, but the heavy fluid hydrocarbons are also formed. This mode of decom- 
position is evidently a mixed one, partaking of the characters of a regulated distilla- 
tion, while at the same moment a more complete destruction of the coal is proceeding 
in some parts of the mass. 
A further decomposition of the fluid products, condensed from either or both of 
these modes of operating, takes place when we again subject them to the influence of 
heat; and this well-known fact is the basis on which improvements in the manufac- 
ture of illuminating gas have been founded,—a secondary destruction of vapours being 
effected in appropriate apparatus, heated to a high temperature. 
This character, which all the bituminous coals exhibit, of passing into carbon nearly 
free from vapours only when heavy fluid hydrocarbons are also formed, has, in a che- 
mical view, been the strongest fact adduced in opposition to the generally received 
opinion that the anthracites and semi-anthracites have resulted from chemical changes 
of bituminous coal, through the agency of the heat of igneous rocks which have dis- 
turbed their beds. The heavy hydrocarbons, represented by ordinary coal-tar, are 
the most indestructible bodies known; and wherever anthracites exist, we should 
expect to find near those products of the chemical changes effected in the coals 
Such is the delicacy of the balance existing between the elements of the heavy hydro~ 
carbons, that no second distillation of them can be effected; they always undergo 
decomposition by heat, with the separation of carbon, which, under any Enown natu- 
ral conditions, would remain to attest their previous presence. 
Considerations of this kind have led me to experiment on the changes which coals 
undergo by heat, where the influencing conditions were not the same as those usually 
seen; and the results of extended trials demonstrate that the bituminous coals may 
be broken up into permanent gases, vapours of water, and ammoniacal salts, while 
carbon remains as a fixed product. 
If we substitute, for the ordinary forms of apparatus used in decomposing coal by 
heat suddenly applied, any modification of form which compels the gas, as it forms, 
to escape from the more highly heated part of the mass of coal, through a small open- 
ing, or, better, a small eduction-pipe, the heavy hydrocarbons do not form part of the 
products which escape. Generally the light, nearly colourless oils of the benzole 
series appear with the aqueous solutions uf the ammoniacal salts, while only an acci- 
dental quantity of carbon is deposited in the eduction-pipe. The carbon left is more 
than usually compact and hard; and such coals as ordinarily produce much water, 
when they form heavy hydrocarbons, afford less than half the usual amount, when 
thus decomposed, under the influence of the constant presence of an atmosphere of 
permanent gases. 
In following the observations at the earlier stage, it was found that the size of the — 
eduction-tube leading the gas from the hotter part of the mass of coal undergoing 
changes, exerted a most marked effect on the composition of the products. It was 
established as a fact, that in an ordinary coal-gas retort, the size of the conduit might 
be varied so as to allow the tar-like bodies to form, or to prevent their appearance at 
leasure. 
< But a more remarkable result was obtained, when, after having prevented the pro- 
duction of heavy hydrocarbon fluids, the influence of reduced size of tube was studied 
in its relation to the composition of the gas afforded by a particular kind of coal. To 
a certain extent, the chemical constitution of the gas formed was found to be under 
control, and the conclusion reached was, that dissimilar permanent gases may be thus 
obtained from the same parcel of coal without a modification of temperature, § 
Any explanation of the change of composition induced in the volatile parts of 
