Assume nothing. Question everything.

When I was still in elementary school and household flashlight batteries were D-cells made using carbon-zinc chemistry, some of those D-cells were set in cardboard tubes that enshrouded a zinc can as in Figure 1 below.

Figure 1 Carbon-zinc D-cell from sixty-plus years ago where the negative post is the zinc can and the positive post is a small tip. Source: John Dunn

I remember taking such cells apart to see what was inside and digging out a center carbon core that connected to the positive post tip. The negative post of the cell was the metal can made of zinc.

I guess that these old battery materials weren’t threateningly toxic, so I got away unscathed for having done that. Doing something like that today, I hate to imagine the possibilities.

In the ensuing decades, I have always naively assumed that the outer cans of D-cells, and other sized cells too, were the negative terminal but I have labored lo these many years under a false assumption.

When two D-cells of a household flashlight recently gave out and I replaced them, for absolutely no reason in particular, I took off the outer cover of one of the used-up cells and got quite a surprise, Figure 2.

Figure 2 In modern alkaline D-cells the can is the positive end of the cell. Source: John Dunn

In these modern products, the can is the positive end of the cell, not the negative.

In terms of the product’s purpose, this difference amounts to nothing significant, but simply finding out this fact drove home to me that some of my lifelong assumptions should not be taken as immutable.

Science fiction writer Robert Heinlein prefaced one of his novels with the quote “Forgive him Caesar for he comes from a far place and believes the ways of his people to be natural law.”

Assume nothing. Question everything. (Many sources.)

John Dunn is an electronics consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York University (MSEE).

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