Working with a caking coal Wright obtained the following results: - Analysis of the tar showed that the increase of the specific gravity was due to the increase in the quantity of pitch, which rose from 28.89 to 64.08% in the residuals; whilst the ammonia, naphtha and light oils steadily fell in quantity, the creosote and anthracene oils doing the same, but to a smaller extent.
This arrangement has the effect that the salts, as they separate out, slide down the sloping part and arrive in the central channel, which is not exposed to the fire-gases, so that they quietly settle there, without caking to the pan, until they are fished out by means of perforated ladles.
The property of caking or yielding a coherent coke is usually absent, and the ash is often very high.
Very important distinctions-those of caking or non-caking-are founded on the behaviour of coals when subjected to the process of coking.
The caking property is best developed in coals low in oxygen with 25 to 30% of volatile matters.