RECENT DEVELOPMENTS IN COAl tTILIZATION 437

 The Rochester Gas & Electric Co. is making a new byproduct— ammonium
thiocyanate—from a combination of the cyanogen, ammonia, and sulphur
in coke-oven gas.23 Ammonium thiocyanate has been found effective as a weed
killer 24 and is a raw material for thiourea resin plastics, which are similar
to transparent bakelite.
 Sniphur from gas.—The recovery of marketable sulphur in the purification
of gas is one of the notable achievements of recent years. The sulphur obtained
by some of these liquid-purification processes is in a very fine state of
subdivision, which has been found advantageous to its utilization as a fungicide.25
 Coal tar and pitch.—The most important recent commercial development
in the treatment of byproduct tar is its partial refining at the ovens, utilizing
the sensible heat of the coke-oven gas for the distillation.26 Hot coke-oven
gases enter a distilling main, where they are showered with a spray of tar.
The hot gases vaporize the tar oils, which are condensed by the cool incoming
tar in heat interchangers. The heavy tar or pitch overflows continuously
from the bottom of the still. The advantages claimed for this process are
low cost, high yields, and flexibility in permitting the removal of only
those fractions which have~a~good~market. The remainder can be utilized as
fuel or charged back into the coke oven. Such recovery units have been installed
on eight coke-oven plants in the United States, with an annual capacity of
36,000,000 gallons of tar. These units produce tar-acid oils, creosote oils,
and a variety of residuals ranging from lightly distilled tars to pitches
melting at 4000 F.
 Some pitch is marketed now in the form of flakes produced on rotating cooled
drums or on water-cooled moving metal belts. Large quantities of pitch have
been used in coating long-distance gastransmission pipe lines, and in the
past 2 years much of this residue has been shipped to Europe for briquet
binders. Such pitch as finds no other market is converted to a lustrous,
dense, extremely hard coke of very low volatile content and almost no ash.
 Marked improvements have been made in recent years in the carbonization
of pitch. One method 27 uses a modified beehive oven, the volatile oils that
distill off serving as fuel for the operation. In another process 28 molten
pitch is sprayed continuously down through the top of a highly-heated byproduct
oven. When the coke has built up almost to the top the entire charge is pushed
from the oven. Recently, the Knowles shallow sole-fired oven has been applied
successfully to coking petroleum pitch.29 The bitumen is sprayed continuously
into the oven, the coke accumulates gradually and, finally, is pushed mechanically
from the oven.
 Manufactured gas as motor fuel.—The question of using gas as fuel
for trucks and automobiles is being raised again in England and
2lShnidman, Louis, Ammonluin Thiocyanste Recovered from Manufactured Gas.
Proc. Am. Gas
Assoc., 1932, pp. 950-976.
2dWeidleIn, E. R., Progress at Mellon Institute during 1931-32. md. and Eng.
Chem., News Ed., vol.
10, 1932, P. 97.
' 5Powell, A. R., Recent Developments in Special byproducts of Coal Carbonization.
Proc. Am. Gas Assoc., 1932, pp. 904—913.
2 Mifier, S. P., Improvements in the Art of Manufacturing and Utilizing Coal-Tar
Products: Jour. Franklin Inst., vol. 215, 1933, pp. 373-399. Weiss, 1. M,
The Distifiation of Coal Tar. Chemistry and Industry, vol. 51, 1932, pp.
248-9.
 2? Barrett Co., Coke and Process of Producing the Same. U.S. Patent 1650126,
Nov. 22, 1927.
 29Koppers Co., Improvements in Coking Bituminous Material. British Patent
337800, Nov. 10, 1930.
 29 Knowles, Alexander S., assignor to Tar & Petroleum Process Co. of
Chicago, Method Of Coking Liquid Hydrocarbons. U.S. Patent 1879983. Sept.
27, 1932.
 Foster, Arch L., Knowles Ovens Solve Residlum-Disposal Problem, Pay Satisfactory
Profit. Nat. Petrol. News, vol. 25, no. 10, Mar. 8,1933, pp. 26-33.