Acharonim (Hebrew - sing. Acharon) literally "the later ones", is a term used in Jewish law and history, to signify the leading Rabbis and Poskim living from roughly the 16th century to the present. The acharonim follow the Rishonim, the "first ones". The Rishonim are the Rabbinic scholars between the 13th and the 16th century following the Geonim and preceding the Shulkhan Arukh. As Jewish law is hierarchic and precedent-based, the opinions of the acharonim are valid insofar as they as based on those of a Rishon.
He answers that Tosafot were trying to offer a defense for the people of their generation who had stopped washing mayim acharonim, and thus they presented to reason of Sodomite salt as the main reason, thus allowing for the possibility of declaring the practice no longer necessary.
However, if the reason for mayim acharonim is due to personal danger, then even in war one must continue to wash his hands to ensure that they are free of any dangerous salts.
Since the point of mayim acharonim is to remove the filth from the hands, the water may not be at a temperature that is so high that it actually produces the opposite effect.
The Acharonim (see Pri Megadim Eishel Avraham 254:1 and Eglei Tal Ofeh 8:11) explain that the stringent view believes that the effect of the cooking of a liquid is nullified after it has cooled down.
Acharonim have debated the definition of liquid and solid in this context for centuries.
Some Acharonim (the Bach, Vilna Gaon, and Mishna Berura) believe that a food must be free of any liquid to qualify as a solid.