I think there was some doubt about its identity. I'm quite prepared to believe that it's a Knox, but I think someone in that book has got it wrong in describing it as a steamer.
Knox's main selling point at that time was its air-cooled gasoline engine, and it was widely advertised as the Knox Waterless. The cars had a very good reputation for reliability, which is probably why Fire Departments were attracted to them. It's not a very good picture, but below is a Knox Waterless set up as a personnel carrier, rather than a chemical truck, from a 1908 magazine. There are many points of similarity to the puzzle car.