The whole bed was a glowing mass, and the heat which rose from it was so intense that we found it uncomfortable to sit fifteen feet away from it without screening our faces with fans.

Then they began to pound it down more solidly along the middle; as far as possible inequalities in its surface were beaten down, and the coals which protruded were brushed aside." There follows a long and detailed description of further ceremonies, the receiving of gifts, etc., which need not be repeated here.

Now for the trick itself.
"One of the priests held a pile of white powder on a small wooden stand.

This was said to be salt--which in Japan is credited with great cleansing properties--but as far as could be ascertained by superficial examination it was a mixture of alum and salt.

He stood at one end of the fire-bed and poised the wooden tray over his head, and then sprinkled a handful of it on the ground before the glowing bed of coals.