Fixer "heavier than water"

[cyrus]

We have all heard of the old "fixer is (denser) heavier than water and will sink to the bottom" line. I thought it was dismissed as a fallacy. But one day I was fixing some reels of MF film in a tall Paterson tank. I added the fixer solution, but ran short of fixer and so immediately added some water to the fixer solution that was already in the tank. (I figured the diluted fixer would still do the job well enough, even if it took longer) Then I was distracted with something else and didn't agitate the tank.

Well, lo and behold, when I removed the center column that held the reels to check the progress of the fixer, the reel on the bottom was obviously clearer than the one on the top. It would seem to support the theory that indeed, the fixer solution sank to the bottom.

[nolindan]

Yes...

If you put a drop of ink in a glass of water it will sit at the bottom and slowly diffuse into the water. If you stir the water the ink will go into solution faster. After the ink is dispersed in the water it will never settle out again as a layer of ink at the bottom of a clear glass of water.

Same with hypo - once it mixes into the water it won't settle out. A good print washer insures it is well mixed because it maintains a good flow of water against the film or print. The concentration of fixer is then uniform throughout the washer.

In your case you poured hypo into the water, where it sank, like the ink. You didn't mix the hypo into the water so it sat at the bottom and slowly diffused in the tank. If you had mixed the hypo into the water then the two reels would have fixed at the same rate.

[cyrus]

Yea but the force of the water being added to the fixer should have mixed them up good! Anyway I hope ur right else I'll have to return my science degree and ask for a refund

[EdWorkman]

Explained by Dr. Henry in his "Controls in B&W Processing"
Brownian movement causes the solution to reach uniformity- if you don't stir it it just takes longer, as Nicholus explained. If not for Brownian movement you might walk into a cloud of say pure nitrogen in a closed room and suffocate, cuz it didn't stayed mixed. No refund.