Found it, and as simon said, geeks3d: http://www.geeks3d.com/20091109/download-the-powder-toy-physics-game/

I have version 4.5 in a backup somewhere......If I ever find it I will post it

this link has all versions from the first to 45.1
https://powdertoy.co.uk/Download/Older.html

or you could go to the home page, click on ''other platforms'', then ''browse'' and finally ''older releases''.
so you should have passed every version so far

@little-ditch
no that only goes to 25 not any lower

i sure i have an old one somwhere, but not sure what ver.

i compared my old one to the oldest one hosted and found the one i already had didnt have plant/acid

@Simon
ohh so thats what they are