I believe this is an early Marklin.  I also think it is an O gauge. It is approx. 7 1/2" long. Stands about 3 3/4" tall.  The cab appears to be tin.  The tank may be brass.  It is heavy at 2.25 pounds.  Has two levers with a ball on each of them in the cab.   Has an 0 embossed on the side of tank.  the wheels from outside to outside is 1 5/8".  That is the best I can tell you.  Hopefully one of you train pros will set me straight on what this is.  Thanks.