When did "Zinc Current" come into (and leave) usage as a term for polarity?

[Gyro]

Ok, one for a quiet Sunday.

Does anyone know when the term "Zinc Current" was in usage as an indication of polarity. I've got an old telegraph Galvanometer which refers to sending or receiving a "Zinc Current" on the dial. Obviously the Zinc electrode would be negative one in the Leclanche cells or whatever they were using to power it. Being a Post Office (UK) telegraph instrument dates it to a certain extent too.

I've searched the web (far too many references to Zinc mining etc) and old tegraphy books but have never seen the term used. Does anyone have any references?

The photos below is taken from my reply to the 'What's your oldest peice of working technology' thread, back in 2015 - Now that's a thread that definitely needs resurecting! https://www.eevblog.com/forum/chat/what's-your-oldest-peice-of-working-technology/msg793702/#msg793702

[hexreader]

Google      zinc current telegraph

My guess it is the current that flows through zinc plate to ground

[Gyro]

Sure, lots of good hits for telegraphy and cell types, I was looking more for references for 'Zinc Current' being used as technical terminology (rather than positive/negative) - assuming that it wasn't an instrument maker's quirk.

[Nusa]

Zinc current and Copper current. I've seen both terms used in print many years ago, in material that was even older than I am. Can't give you a reference, sorry.

[Gyro]

Thanks Nusa. I did wonder if 'Copper current' might be the partner term.

I suppose this might tie up with the time that 'Positive' and 'Negative'  came into common engineering usage - alternatively it might be related to the (possibly?) more limited but specific training given to Telegraph staff, rather than general Electrical engineers. Something that matched up more clearly with the equipment they were working with.

[Nusa]

Google, including the quotes to eliminate single-word results: "zinc current" "copper current"

You'll get a bunch of book and patent references circa 1900ish. Have fun.

[Gyro]

Thanks, I did try that before but kept getting a lot of 'Zinc current price' type results. However '"Zinc Current" Galvanometer' is yielding some useful stuff (including this thread on eevblog!) I must surely have tried all sorts of such strings in past years though, weird... and slightly embarassing! 

[Gregg]

It could be a reference to zinc carbon battery polarity; the zinc case being negative in today's terms