Ref. No. 820. "16 Seam," same colliery as above-inch Slack.

1

These tests show that inch slack, i.e., the portion of the run-ofmine coal which will pass through a screen of inch aperture, is more amenable to cleaning than the aggregate run-of-mine coal from the same seam.

From the above results it will be seen that the practice of using slack for brick burning or as boiler fuel and, frequently at the same colliery, of crushing run-of-mine coal for coking is wrong. Slack should be cleaned for coking.

This preferential crushing of the better constituents can be carried a stage further. The -inch slack produced during mining may be about 10 to 15 per cent. of the coal mined. Coals which are not sufficiently amenable to cleaning to be commercially cleanable as run-of-mine coal may be utilized in the following manner. Further preferential crushing may be obtained by breaking the run-of-mine coal to about 1 inch in a toothed roll type of crusher. The crushed coal, screened on sayinch, will give rubble (—11⁄2 inch, + 1⁄2 inch) suitable for boiler firing, and "fines" (-inch) which may be cleaned for coking. Results obtained in this manner from a tramload of coal cut as a face sample are given below:

Ref. No. 552. "16 Seam," Jharia area. Run-of-mine, unpicked. Ash 22-4 per cent.

Crushed to 1 inch, screened on 1 inch aperture screen, this gave the following products :

Rubble, hand-picked

Weight per cent.

Ash per cent

Fines (Ref. No. 551).

Crushed to 1 inch, screened on

inch aperture screen, the

same run-of-mine coal, Ref. No. 552, gave the following products:

It will be noted that hand-picking of material smaller than 1 inch has not been attempted, and that the analysis of the material picked out, ash 57.8 per cent., is an indication of the fact that there is sufficient difference in the appearance of the clean rubble and the rejected pieces to allow of picking by unskilled labour.

The word "fines" is used in the special sense of meaning the portion of the crushed run-of-mine coal which will pass through a screen of the aperture indicated. It will be noted on page 236 that a similar product from uncrushed run-of-mine coal is called "slack”. Hence, fines is made up of slack plus small material produced by mechanical crushing subsequent to mining.

Tests have been done on both 1 inch and inch fines for comparison. The greater cleanability of fines is shown by the following results of tests :

Ref. No. 552. "16 Seam," Jharia area. Run-of-mine, unpicked. Ash 22.4 per cent.

Ref. No. 550. -inch Fines. See p. 238. Ash 19-2 per cent.

These results show that a seam, which may not be commercially cleanable as run-of-mine coal, may be crushed to give rubble for boiler-firing or for general purposes, and fines cleanable for coking. The tests done are sufficient to prove the applicability of the suggestion. Further details, such as the amount of crushing to be done and the mesh of the screen to be used for separating the rubble and fines, may be determined by further tests in special cases, when the particular conditions and the financial details of the proposition can be taken into account.

GIRIDIH.

As Giridih is a small field of good quality coal, samples have not been tested.

BOKARO.

Kargali Seam.

The Kargali seam is a coking coal, which is capable of being cleaned as shown by the following results:

Ref. No. 356. Kargali Seam, Face sample. Ash 22-3 per cent.

Ref. No. 402. Kargali Seam (same colliery as above)
-inch Slack. Ash 20.6 per cent.

Ref. No. 815. Kargali Seam, Top Section. Face sample.

Ref. No. 811. Kargali Seam, Top Section. 1 inch Slack.

Ref. No. 817. Kargali Seam, Bottom Section. Face sample.

Ref. No. 812. Kargali Seam, Bottom Section,-inch Slack.

The above results show that slack from the Kargali seam is amenable to cleaning. The clean product from the Kargali coal has been made into coke of excellent quality.

Bermo Seam.

The coal of this seam is very homogeneous. Heavy liquid separation shows that it is incapable of being cleaned.

BARAKAR AREA OF THE RANIGANJ FIELD.

The coals obtained from the neighbourhood of Barakar in the Raniganj field, have a moisture content of less than 1.5 per cent. and are coking. Results of tests on face samples are given below:-Ref. No. 257. Laikdih Seam. Ash 14.0 per cent.