I weigh an iron block by suspending it from a set of scales in the air. I then submerge the iron in a pail of water (still suspended from the scales). The iron block does not touch the bottom of the pail and I notice that the measured weight goes down when suspended in the water. If I now place another separate metal block in the pail (which sinks to the bottom and raises the water level), the apparent weight of the suspended iron block will