Drying time for wet iron sulfate and salt with some sun

In the previous experiment we showed that a mixture of table salt and iron sulfate can absorb H2O from water ice in a near vacuum.   In this experiment we are testing how long it takes for wet mix of salt and iron sulfate to dry out with partial sun.   On Mars the RSL paths take many days to fade away so we are hoping for a similar result here.

Note this is not in a vacuum and using partial Earth strength sun instead of Martian strength sun.  Mars has far less atmosphere blocking UV.  We live near the ocean so the humidity is far greater than on Mars.  Also, we are not saying that Mars is 50% table salt and 50% iron sulfate but just hope that this mixture makes a reasonable analog for showing the ability to absorb H2O from ice while at low pressure and taking a long time to dry out.    So this is far from an exact simulation of Mars conditions but if it does take many days to dry out that will still seem interesting.

We mixed about 50% table salt and 50% iron sulfate.

We weighed them before and after adding some water.  Note it is far darker where it is wet.

Then put them on a temporary shelf by the window so they can get some sun.  The 2 on the left and the one on the far right are expected to get less sun and dry out slower.  Note that science does not care what your name is or how old you are.

March 13, 9:00 am

We will weigh them each day and record the results in the book and with pictures.  If you click the above picture it gets large enough that you can read the weights in our lab book.    Note that the wet part is spreading out and smoothing out over time.


So it seems iron sulfate can combine with O2 from the air and turn brown.   We are seeing some brown so probably this is going on.

March 13, 1:30 pm

After 4 1/2 hours (3/13/16 1:30 pm) the sun was no longer on the samples and we weighed them.  Note that the color is a much more smooth green now.   The #1 sample gained 0.1.  This could be from absorbing oxygen or from measurement error.  The others on average lost about 0.2 grams. It is not drying out too fast, so it could be an analog for RSL fading.   Ya!  :-)   More measurements coming.

Still first day but 7:30 pm.  So 10 1/2 hours and 6 hours from last measurements.  Samples 3-6 still lost a bit of weight even without sun.

March 13, 7:30 pm

March 14, 8:25 am

March 15, 9:13 am

March 15, 4:00 pm

March 16, 7:30 am

Even after 3 days it would seem drying out is going to take a long time.  Assuming it does eventually dry out, this could show behavior similar to RSL paths.   There is still some chance that the salt in our humid environment just never dries out.   More data coming.

One theory about RSLs is that there is salt in these paths and they change color as they absorb water from the air.  I don't believe this because any particular section of path always suddenly becomes dark as if an avalanche had suddenly made it all dark.   You can get sequences of pictures showing that they fade (assume dry out) over many days but there do not seem to be any sequences of pictures showing them gradually getting darker over any particular section of path.  Even our humid environment with dense air absorbing moisture from the air is a slow thing.  On Mars this would have to be very slow, so if it was happening there should be pictures sequences where they get darker.  Also, there can be one dark path and then suddenly another dark path next to it.  Salt on paths absorbing water would all go at the same time.  So avalanche fits the data better.

At 4 days there is clearly some sort of crystal growth.  It seems this growth is more in the more shaded samples or parts of samples.  I have to wonder if as it grows these crystals there will be more surface area and so it will then be able to dry out.  It could also cause a fading of color on the surface even if the part below was not yet dry.   Interesting.  If you right click to "open image in new tab" you can then zoom in to see more detail.

Since there is some oxidation going on it probably can not return to its original color even when dry.  So I now think we will want to do this again using the resulting mixture as the new starting point.
Again note that if you right click and "open image in new tab" you can then zoom in for more detail.

3/20/16 1:00 pm

3/20/16 1:00 pm sample #1

Zoom of sample 1

3/21/16   8:00 am

3/22/16  5:00 pm

zoom of #4 - click then right click to open in new tab for even more zoom

digital zoom of #4

I thought crystals had to be grown in a solution, I did not know you could grow them like this.  Surprising how it must work.  I guess salt water is flowing up the sides of the crystals and then drying.  To me this is an interesting result.  It seems it could be going on in Mars RSLs too.

Googling I find that when salt is coming out of damp masonry and making crystals it is called Efflorescence.

3/23/16  6:00 pm

zoom of #2

3/24/15  5:50 pm

3/25/16  11:30 am

zoom of #6

3/26/16 11:30 am

zoom of #1

3/27/16  both am and pm

3/28/16 both am and pm

Started weighing both in morning and at night.  It is losing weight (water) during the day and gaining some back at night.

Microscope on sample #1 at 3/28/16 midnight

Results (some even while experiment is ongoing):
1) A mixture of table salt and iron sulfate takes a long time to dry out, well over a week.
2) It seems to need to make crystals to dry out, which takes a long time.
3) It can lose water in the day and gain some back at night