What's "dry steam"?

I have a Swiss book which explains the wheel-arrangement notation in use in Switzerland and elsewhere, in which, e.g., a Pacific (counting axles rather than wheels) appears as 2'C1'h2, with the apostrophe indicating truck-mounted rather than on the frame, and 2 the number of cylinders. There are three possible letters preceding the number of cylinders:
n = "nassdampf", literally "dry steam", evidently saturated;
h = "heissdampf", "hot steam", presumably superheated;
t = "trockendampf", "dry steam".
The t rarely appears--does anyone know what "dry steam", as opposed to superheated steam, might mean, and since it apparently never caught on, what the reason might have been?

(I found a listing in Wikipedia, and it seems to be something used in industrial cleaning, but no explanation of how it's produced, and no mention of its use in steam locomotives.)

Dry steam is superheated steam. The higher temperature steam has relatively less free moisture.

Typo in your initial post: "Nass" means "wet" (as your gloss of "Nassdampf" as saturated steam implies).
I've never encountered two distinct words for ... drier ... steam before. Four guesses (and I mean GUESSES): One is more superheated than the other? Certainly the degree of superheat varied with different steam designs, and I suppose some classifier might have thought to distinguish between steam that was only superheated a bit and steam that was MUCH hotter than saturated.
Second guess: a few compound locomotives "resuperheated" steam between its use in the high pressure cylinders and its use in the low pressure cylinders.
Third guess: Heissdampf is steam for heating: so, in passenger engines, the steam which, instead of being used for propulsion, is diverted into steam lines to provide heat in the cars. (No, this one probably isn't it: position of the letter in your example suggests steam that WAS used in the cylinders.)

Any of these make sense in the context of your book?

In the years after 1900 a steam dryer was a try to achieve a cheap "low grade" superheated steam. It soon was a failure.

https://oi25.photobucket.com/albums/c63 ... g~original

The "t",is the abbrevation of "Tenderlokomotive" (Tank-Engine)
For example, a "Bn2t" is a Tank-engine(t) with two coupled, driven axles (B), with "Nassdampf" (="wet steam")(n), two cylinders (2).
https://commons.wikimedia.org/wiki/File ... eim_05.jpg
Or another one, a "2'C1'h4v", is Pacific-Type engine, with leading bogie(2'), three coupled, driven axles(C), a trailing axle(1'), with "Heissdampf" (=superheated steam) (h), with four cylinders(4), working in compound (v).
http://www.uef-dampf.de/-hauptverein/pa ... 18316.html

The steam needed for heating the coaches is called "Heizdampf", from "Heizung"(=Heating), not to be confused with "Heissdampf", although it sounds almost the same. The "Heizdampf" was usually taken out of the main steamdispenser (I don't know the english word for it), where all auxiliary steam was diverted off the boiler. It was NOT superheated and NOT dried, so the steam-coupling hoses between the coaches, as they're the lowest point, had small openings to let the condensing water dripple out. https://www.fotocommunity.de/photo/ich- ... ng/7320521

Allan Hazen, I never noticed the typo. I forgot--always reread after you change anything!
Motorman, I see now that the "v" means compound; I've seen the term Verbundlokomotive and was never able to find a definition.
bengt, your explanation seems the most likely; thank you.

I took another look at the Swiss book (Illustrierte Geschichte der Eisenbahn, Schweizer Buchzentrum, 1976), and there's an asterisk next to Trockendampfbauart stating that it's obsolete; no longer used by locomotives in service--so it looks like it may have been tried and found wanting.