THE GAS COALS OF OHIO. ‘ 745 
laundries, and for heating residences and places of business ; the harder 
- grades being usually crushed, and the more porous and lighter grades 
used as they come from the gas retorts.’ | 
The Ohio coals produce about 60 per cent. in coke of the weight 
of the coal charged. The best Youghiogheny and Kanawha coals pro- 
duce from 65 to 72 per cent. of the weight of coal charged in retorts. 
A simple analysis cannot determine the value of coal for gas 
purposes ; for, as is shown in the instances referred to, the coal that sends 
off the largest volume of gas leaves behind in the retort the heaviest 
weight and best character of coke. 
For many purposes gas coke, when cost and heat producing power 
are considered, is the most desirable fuel that can be obtained. It is 
light, weighing from 33 to 40 pounds to the bushel. Clean and free 
from the dust and smoke of our soft coals, and unlike oven coke, it does 
not require excessive draft to produce proper and rapid combustion. — 
Containing nearly double the quantity of ash that coal contains, theor- 
etically it should be inferior to coal. But when we consider that the 
volatile portion of coal, as the coal is burnt in the ordinary stove and 
grate, often furnishes but little more than enough heat for its own 
expulsion, and in fact carries off by expansion more units of heat than 
it produces, the value of gas coke as domestic fuel is then fully realized. 
While tar ranks second in value, when disposed of in the crude state, 
it is possible to extract from the tar of a ton of coal, compounds ofa 
value far in excess of all other products—gas, coke and ammoniacal 
liquor. 
The quality of coal tar is largely influenced by the temperature of 
the retort in which the coal is charged. A large volume might be writ- 
ten on coal tar and its compounds, but in this work it will only be 
possible to give a very general description of its characteristics and 
products obtained by its distillation. It is doubtful if it is possible for 
an analysis to be made of coal tar that will show the combination of 
the elements of which it is composed, as it flows from the retorts. An 
ultimate analysis would show chiefly carbon and hydrogen, yet the 
various compounds of these elements cannot be ascertained, as the very 
act of analysis itself destroys and changes their character. About one 
hundred and twenty different compounds are named as being found in 
tar. Coal distilled at a low temperature gives off tar in abundance, 
and the tar is rich in hydrocarbons of the paraffine series. But if the 
