She nodded.
"Can you speak for him?"
"You talk, I hear, he reads me. I read him and I can speak."
* * * * *
"Okay, then," said Lou Graham. "Now we build a Le Clanche cell. Ask
Harla does he recognize carbon. A black or light-absorbing element.
Carbon is extremely common, it is the basis of life chemistry. It is
element number six in the periodic chart. Does Harla know carbon?"
"Harla knows carbon."
"Now we add zinc. Zinc is a light metal easily extracted from the
ore. It is fairly abundant, and it is used by early civilizations for
making brass or bronze long before the culture has advanced enough to
recognize zinc as an element. Does Harla know zinc?"
"He may," said Teresa very haltingly. "What happens if Harla gets the
wrong metal?"
"Not very much," said Lou. "Any of the light, fairly plentiful
metals that are easily extracted from the ore will suffice. Say tin,
magnesium, sodium, cadmium, so on."
"Harla says go on."
"Now we make an electrolyte. Preferably an alkaline salt."
"Be careful," I said. "Or you'll be asking Harla to identify stuff from
a litmus paper."
"No," said Lou. He faced Teresa and said, "An alkaline substance burns
the flesh badly."
"So do acids," I objected.
"Alkaline substances are found in nature," he reminded me. "Acids
aren't often natural. The point is that an acid will work. Even salt
water will work. But an alkaline salt works better. At any rate, tell
Harla that the stuff, like zinc, was known to civilized peoples many
centuries before chemistry became a science. Acids, on the other hand,
are fairly recent."
"Harla understands."
"Now," said Lou Graham triumphantly, "we make our battery by immersing
the carbon and the zinc in the electrolyte. The carbon is the positive
electrode and should be connected to the start of our electromagnet,
whereas the end of the winding must go to the zinc. This will place the
north pole to the left hand."
"Harla understands," said Teresa. "So far, Harla can perform this
experiment in his mind. But now we must identify which end of the steel
bar is north-pole magnetic."
"If we make the bar magnetic and then immerse it in acid, the north
magnetic pole will be selectively etched."
"Harla says that this he does not know about. He has never heard of it,
although he is quite familiar with electromagnets, batteries, and the
like."
I looked at Lou Graham. "Did you cook this out of your head, or did you
use a handbook?"