The Wikipedia entry on slack lime gives slaked lime as an interchangeable or alternate common name. Both are hydrated (some water already incorporated) forms of calcium carbonate, that is considered quite safe in normal handling, and having no explosive properties or tendencies. It is safely used in making whitewash (paint) or plaster, and has been used in mortars for bricks but isn't particularly good for that.

It is used as a "floculent" to aid settling out of small particles, and as an "acid reducer" to minimize corrosion in some municipal water supplies.

It is a component in a number of food and cosmetic products, although the Wikipedia entry fails to mention its use in making "lime pickles."

It was used by some in "outhouse pits" and the belief persists that it facilitates the breakdown of the shit pit contents. This, however, has been verified as being a "mythic belief" as "liming" the pit actually preserves the contents of the pit. It does "buffer" the acidity of the contents and reduces the emission of "odorous gases."

I don't see a way that this product might have been applied to produce the results suggested in this thread. A sufficient quantity of lime could raise the pH of the water sufficiently to be harmful to a few fish, but even this effect would be questionable.

An alternate product that was fairly commonly available in the time frame suggested could have been "carbide." Calcium carbide reacts with water to produce ethylene gas (C2H4), and it was used (rarely?) for generating "lantern gas" or "stove gas." Industrially, large generators capable of producing "carbide gas" in large volumes were used in "welding shops" since the ethylene is what is now called acetylene.

Ethylene gas has the property that it will detonate if confined at pressures above a couple of hundred psi. In modern usage, it is always dissolved in a small amount of acetone retained in a porous charcoal filler in the higher pressure tanks in which it is stored, transported, and used for welding. In solution with the acetone it remains inert up to the thousand or so psi at which "acetylene" is commercially available.

It is possible that water entering holes in a jar lid could start a carbide process that would build up pressure at a rate faster than the water could be blown back out, resulting in a rather powerful explosion.

In the 1920s, IIRC, the Trailways bus line had a maintenance shop at Kip, Kansas, capable of containing 6 buses with adequate surrounding work spaces. The shop had a "carbide generator" consisted of a six foot diameter cast iron dome that was "floated" in a tank of water by the gas pressure in the dome. Carbide "rocks" were fed into the water to maintain the generated gas at a nominal and safe pressure.

One day, the dome stuck, and the pressure began to rise.

The only applicable response was well known by all those working there:

     RUN LIKE HELL!!!!

There has never been a Trailways maintenance shop in Kip since that day - or any visible remains of the previous shop requiring picking up the pieces, according to a former father-in-law who ran with the rest of the shop people (and axxording to him, faster than some).

John