Abstract
So far the word of washability has been used only to indicate the relation between the ash content of washed coal and its yield, but it should also have the meaning of the relation between the yield and the contents of sulphur and nitrogen and coke button index of washed coal which are the other variable factors in washing.
The washability curves of 14 Japanese coals and 5 imported coals have been made and the results obtained are as follows:
1) there are close relations between the inherent content of sulphur and nitrogen and the inherent coke button index and those of the original Japanese coals respectively, and
2)the qualities of washed coal increased in general with the exception of some coals with the decrease of the yield.
