He was saving the coins to keep Schwartz going.

When the last coin went, Schwartz would give out.

It all sounds queer now, but it seemed all right then--and it WAS all right, too.
So we walked on the beach, losing entire track of time.

And after a long interval I came to myself to see Schwartz lying on the sand, and Denton standing over him.

Of course we'd all been falling down a lot, but always before we'd got up again.
"He's give out," croaked Denton.
His voice sounded as if it was miles away, which surprised me, but, when I answered, mine sounded miles away, too, which surprised me still more.
Denton pulled out a handful of gold coins.
"This will buy him some more walk," said he gravely, "but not much." I nodded.