temperature at which the pellet has collapsed due to softening to one-half its original height. It must be noted, however, that while this arbitrary temperature is of value in grading coals as to their probable clinkering tendency, the loss by clinker formation in the

boiler fires can only be governed by the length and position of the softening range which in turn governs the nature of the fusion.

(f) Calibration of the Instrument.

For a new instrument with a platinum rhodium couple of unknown milli-voltage temperature scale, a most ready means of

calibration presents itself. Test cylinders of pure metals or standard substances having sharply defined melting points are placed in the furnace "A" in the usual position for an ash cylinder, and the fusing curve developed as described in the previous paragraphs. Since the Fusiometer was designed primarily for the investigation of coal ash fusion, its working temperature range will be between 1900° F. and 3000° F. It has, therefore, been considered sufficient, in calibrating this particular instrument, to develop two points only, and for this purpose nickel and copper were selected.

It will be noted in Figure 6 that the copper point is sharply defined, the two curves substantially checking and showing a very short softening range. The nickel point is also sharply defined, but this metal appears to have a longer softening range in comparison to copper.

The following illustrations show curves developed from a number of ash tests, using this instrument, together with Boiler House reports in regard to the nature and extent of clinker formed under actual operating conditions.

TESTS NOS. 6983 AND 7101-(Figure 7)

Both of these coals, which were mined in Middle Pennsylvania, were tested under Rust Boilers with Taylor Stokers, using a forced draft equivalent to two inches of water in the ash pits. The laboratory results were as follows:

No. 6983. This coal burned freely, with a long flame, the only undesirable point being the formation of large clinkers, which did not, however, cause a serious amount of trouble.

No. 7101.-Proved so troublesome on account of clinker formation, that the remaining cars of this shipment were rejected. Required 45 minutes to clean fires after six hours running.

It is rather interesting to note that although there is less than

100° F. between the final softening temperatures of these two ashes, the one having the higher melting point (Test No. 7101, Figure 7, Curves No. 3 and No. 4), gave the most trouble in the boiler room. From the shape of the curves and the nature of the final pellet fusion, the latter ash has a long fusing range, a high viscosity throughout the range, and finally forms a close gummy clinker,

difficult to remove from the dead grates of a boiler fire box at cleaning periods.

In like manner, for Test No. 6983, Figure 7, the dip in curves No. 1 and No. 2 indicates low viscosity of the meld and the formation of a porous clinker, easily broken up and removed from the fire box.

These two samples illustrate the wide variation in viscosity of meld, between ashes fusing at approximately the same temperature, and the futility of using only the relative ash fusing temperatures to grade coals as to their probable freedom from clinkering trouble, without considering also viscosity and length of softening range.

TESTS NOS. 7124, 7137, 7142, AND 7155-(Figure 8) These coals were mined in Middle Pennsylvania, except No. 7142, which was a slack gas coal from West Virginia.

No. 7124. Free burning long flame coal-burning at a high temperature. The writer witnessed one cleaning of the fire after six hours' operation, at which time it required only the dumping of the back grates to completely clean the fires, this operation consuming two minutes. At other periods it was claimed that this coal gave considerable trouble. This could readily occur at 2500° F. due to the high viscosity at this point, as shown by curves 7, 8, and 9, Figure 8.

No. 7137.-A very undesirable fuel on account of the radical clinkering quality of the ash. A tough, gummy clinker formed requiring from twenty to forty-five minutes to remove at fire cleaning periods.

No. 7142.-Free burning long flame coal which burns at a very high temperature. Not entirely satisfactory on account of clinker formed, which, however, can be handled. The combustible loss in the ashes from this coal was high.

No. 7155.-Free burning coal, forming a soft not very troublesome clinker.

HIGH FUSING ASH FROM MIDDLE PENNSYLVANIA DISTRICTS

(Figure 9)

These coals were all given a trial under Rust Boilers with Taylor Stokers, under forced draft, using a pressure in the ash pit equivalent to two inches of water. The following analyses were made on the several samples, while curves obtained from fusion tests are shown in the illustration.