Derby answered willingly.  “I can give you a general idea.  I was forced into inventing a new method of mining on account of the quicksands, which are found all through our mines at home.  Taking a suggestion from the oil wells, I bored just such a well down into the sulphur beds.  Ordinarily the sulphur is brought up in powder or rock form, and refined in vats on the surface, so that not only do the miners have to go down into the sulphurous heat, but the caldrons in which the sulphur is refined give out gases that are unendurable to human throats and lungs.  In our mines, the sulphur is now refined sixty or a hundred feet below the surface of the ground, and pours out in an already purified state, at the top of the well.”

Sansevero looked incredulous.  “But sulphur is almost impossible to liquefy.  Unlike metals, it congeals again when it has been heated beyond the proper temperature.  Also it corrodes any metal it touches, so that a pipe would be eaten away immediately.”

“To get over those difficulties is exactly what I am trying to do by my new process,” Derby answered.  “The sulphur is melted by hot water sent down the pipes, followed by sand, and then sawdust—­the sand to carry the heat to the cooler edges, and the wet sawdust to check the heat at the center.”

Even the princess drew nearer and laid her hand on her husband’s arm as Derby made his explanation.  Sansevero trembled with excitement.  “But according to that,” he cried, turning to his wife; “our mine would be practicable!” Then to Derby:  “I ought to explain to you that we have a sulphur mine in Sicily, near Vencata.  So far as I know, the sulphur does, as you say, lie in a bed some twenty meters down.  Above it are rock and alluvial soil.  The volcanic neighborhood makes the temperature below ground higher than can be borne, yet we know that the sulphur deposit is immense.”

“Give me more details.  From what you say, it sounds as though this mine of yours might be exactly what we are looking for.  Does Mr. Randolph know of it, or that you are the owner?”

“No; no one knows it excepting one small group of sulphur owners.  I unwisely went into it on the advice of—­some one who is very good at all these things; yet the best are liable to mistake.  Other mines in the neighborhood, owned by friends of mine, have brought in a fortune.  Ours has, so far, been a failure.”

The talk lasted until luncheon was served.  Giovanni put in an appearance, and Derby was pressed to stay.  As di Valdo and the American met, there was a barely perceptible coldness under the Italian’s good manners, while Derby’s greeting showed a momentary curiosity.  Two more sharply contrasted beings could hardly have been brought together.  But gradually Giovanni also became interested in the mining plans, and, as the reason for the American’s coming to Europe very evidently was business and not the pursuit of the heiress, Giovanni’s affability became genuine.