He dipped a dried blade of grass in the bottle and then let a drop fall from its tip in the water.

The water remained unchanged.
"Now throw a little salt in the water," said the stranger.
Concho did so.

Instantly a white film appeared on the surface, and presently the whole mass assumed a milky hue.
Concho crossed himself hastily, "Mother of God, it is magic!" "It is chloride of silver, you darned fool." Not content with this cheap experiment, the stranger then took Concho's breath away by reddening some litmus paper with the nitrate, and then completely knocked over the simple Mexican by restoring its color by dipping it in the salt water.
"You shall try me this," said Concho, offering his iron ore to the stranger;--"you shall use the silver and the salt." "Not so fast my friend," answered the stranger; "in the first place this ore must be melted, and then a chip taken and put in shape like this,--and that is worth something, my Greaser cherub.

No, sir, a man don't spend all his youth at Freiburg and Heidelburg to throw away his science gratuitously on the first Greaser he meets." "It will cost--eh--how much ?" said the Mexican eagerly.
"Well, I should say it would take about a hundred dollars and expenses to--to--find silver in that ore.

But once you've got it there--you're all right for tons of it." "You shall have it," said the now excited Mexican.