CHAPTER XXI.
NOVEMBER 21st to 24th .-- There was assuredly no time to be lost before we ought to leave Ham Rock reef.

The barometer had been falling ever since the morning, the sea was getting rougher, and there was every symptom that the weather, hitherto so favourable, was on the point of breaking; and in the event of a gale the "Chancellor" must inevitably be dashed to pieces on the rocks.
In the evening, when the tide was quite low, and the rocks uncovered, Curtis, the boatswain, and Dowlas went to examine the ridge which had proved so serious an obstruction, Falsten and I accompanied them.

We came to the conclusion that the only way of effecting a passage was by cutting away the rocks with pikes over a surface measuring ten feet by six.

An extra depth of nine or ten inches would give a sufficient gauge, and the channel might be accurately marked out by buoys; in this way it was conjectured the ship might be got over the ridge and so reach the deep water beyond.
"But this basalt is as hard as granite," said the boatswain; "besides, we can only get at it at low water, and consequently could only work at it for two hours out of the twenty-four." "All the more reason why we should begin at once, boatswain," said Curtis.
"But if it is to take us a month, captain, perhaps by that time the ship may be knocked to atoms.

Couldn't we manage to blow up the rock?
we have got some powder on board." "Not enough for that;" said the boatswain.
"You have something better than powder," said Falsten.
"What's that ?" asked the captain.
"Picrate of potash," was the reply.
And so the explosive substance with which poor Ruby had so grievously imperilled the vessel was now to serve her in good stead, and I now saw what a lucky thing it was that the case had been deposited safely on the reef, instead of being thrown into the sea.
Picric acid is a crystalline bitter product extracted from coal-tar, and forming, in combination with potash, a yellow salt known as picrate of potash.