“Oh, I guess you’re right—you most always are,” Dick admitted, making a wry face. “But I’m going to hold you to that coming-back promise before we leave this part of the country. I want to see where this cave goes to.”
Having settled it that way, they packed and struck out for one of the tungsten prospects they had found some ten days earlier, reaching it in good time to pitch a sort of semi-permanent camp near-by.
Wolframite, scheelite, ferberite and huebnerite, all mineral combinations from which the metal tungsten is obtained, occur in a number of curiously different formations, sometimes in the limestone, sometimes in the red sandstones and shales, sometimes in veins whose walls are granite or gneiss. What the three young prospectors had found, or believed they had found, in this first location was a vein of scheelite—which is the tungstate of calcium—lying along a “fault” contact between vein walls of granite and gneiss.
It was a good-sized vein, big enough to be pretty valuable if it were really scheelite, and they ran another test on it to make sure, before they should waste any labor on the “discovery” work required by law—namely, the sinking of a shaft or the driving of a tunnel for at least ten feet on the vein.
The test, in which Larry handled the blowpipe and Dick and Purdick made the notes, seemed entirely successful. The creamy yellowish ore fused with considerable difficulty in the blowpipe flame, as the book said it should; powdered, it dissolved freely in hydrochloric acid, leaving a greenish-yellow residue, and this residue, rubbed with a knife-blade on a bit of paper, changed at once to a bluish-green color.
“That’s the stuff,” said Dick. “Now try it with the phosphoric acid.”
Larry poured a little of the dissolved ore into a glass tube with a closed end, added phosphoric acid, and held the tube in the flame of the alcohol heating lamp. When the mixture began to give off the fumes of volatilization, he took the tube from the flame and let it cool. In a minute or two the test sample turned a beautiful blue.
“Right, again,” said Dick. “That’s what it ought to do. Now dissolve it in water and see if the color will disappear.”
Larry added the water, and immediately the blue color vanished.
“Check once more,” Purdick said, with his finger on the place in the mineralogy book where the various steps in the test were set forth, with their results. “Now a pinch of the iron powder.”