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## Resolved What is the Maximum Saturation of Epsom Salt at 93.5°F

1. Kane Mantyla
2. Epsom Salt
3. Monday, May 18 2015, 05:11 PM

This question has come up several times so here is a graph showing the saturation of MgSO4• 7 H2O (Magnesium Sulfate Heptahydrate, Epsom Salt) at various temperatures.

Since 1mL of water is 1 gram and the data is grams of Epsom Salt per 100mL of water, the conversion of water to weight, and the conversion of weights to percetage is very simple.

At 93.5°F, 30 grams of Epsom Salt will disolve into 100mL (100g) of water. The maximum saturation is 30%

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I ain't no expert but common sense helped me. Took 100ml of destilled water at 35C. Poured in my epsom salt and found out that about 80g+ dissolved. When putting in more than 90g I could see over a few minutes that tiny little crystals were floating around.

So what does that say ? Every salt tends to absorb water from the air. That's why the epsom salt you buy is mostly MgSO4 x 7 H2O, it means there is 51.2195122% water.

.......................................................................................................................

(M(MgSO4.7H2O) = [24+32+(4x16)+(1x14)+(7x16)]gmol^-1

= 246gmol^-1

M(H2O) = 7X(16+2) = 126gmol^-1

%H2O = (126/246)X100

= 51.2195122%)

.......................................................................................................................

Knowing that checked wiki for the Solubility table: https://en.wikipedia.org/wiki/Solubility_table

It's 42,2g of clear MgSO4 /100ml destilled water at 35C

So now when we know that MgSO4.7H2O has like 51% of water in it. It fits with my test that around 80g+ dissolved in 100ml of destilled water.

So the info on http://www.800mainstreet.com/9/0009-004-solub.html does not add up... maybe they did not use destilled water or something...
1. TheGoD
2. more than a month ago
Responses (2)
0
Undo

In the case of the solubility (melting point) for epsom salt, from what I calculated it requires a temperature of 122 degrees farenheit to disolve 100 ml of epsom salt. So I am going to get an expert to weigh in on this because according to my math WE ARE ALL DOING IT THE HARD WAY OR WRONG. In a float room there is 180-200 gallons of water, there is 900 pounds of epsom salt. Anyone who has filled a room or a tank will tell you that melting the salt and getting it to disovle is a huge part of the whole job.

I have studied the rate at which the USP grade salt melts because I have filled rooms around the country and every where you go you get a different water source to work with. Hey I have been places where the water is green, plus calcium and magnesium.

Anyway the water source places a large part in disolving the salt, and if we are supposed to be disolving it at a temperature of 122 degrees in order for it to become soluable and not greasy, then someone needs to raise the required temperature on the hot water heater because in most states by law the don't set it higher than 104 degrees.

Just to make sure I am going to be contacting the head of horticulture chemistry at Ohio State, Glen Schlueter of Wisconsin, and Scott Webb, the writer for Aqua Magazine who does all the water chemistry for the University of Wisconsin.

Okay everyone let me just start by saying I am not trying to offend anyone, I want everyone in the float industry to be informed and educated, and I have had to search for people who had actual knowledge.

Comment
86-87 degrees is my reference point as well.

A hose can be run directly from the water heater to bypass anti-scald caps.
1. FloatationTanks.com
2. more than a month ago
thanks a bunch for your reply. I would also like to see the input into your calculations.

Just based on experience (800lbs Epsom salt into 180 gallons water at 120 degrees F) that the salt will immediately drop the temperature of the water well below 90 degrees when the water has reached 180 gallons. At this point much of the salts are undissolved and require agitation. I understand the amount of salt into the amount of water is less than maximum saturation (which I don't recommend for floating anyways as it is too "stiff" and causes more neck issues), but I am still able to dissolve it all at about 86 degrees. I do wish I had more precise numbers to perform accurate calculations.
1. Kane Mantyla
2. more than a month ago
Hi Cheri, can you share the basis of the temperature calculation?

Do you filter the water through a carbon filter placed on the end of the hose? I'm curious how many people do this or why they wouldn't. It seems like an inexpensive way to greatly reduce hard water issues, chlorine, etc.
1. FloatationTanks.com
2. more than a month ago
1. more than a month ago
2. Epsom Salt
3. # 1
0
Undo

This is very helpful, Kane, thank you. I'd heard that solubility for MgSO4 falls off a cliff at around 50 degrees F, and therefore people in colder climates needed to keep the float tank room heated so that monster crystals would not form in a tank's external unit and tear up the pump and filters. The external unit is not as insulated or buffered as much as the tank itself, and space heating could be required e.g. in a home tank in an unheated basement.

So basically .. and my guess the line is actually curved not linear? ... you can estimate the number of grams of undissolved Epsom salt per degree of temperature drop. In a tank which has a liner, as you point out, this can be issue depending on how the formation occurs.

And it looks like at 93.5 the water of the Dead Sea is a 5 to 6 percentage points more dense than a float tank. Hmm...

Good stuff, thanks for sharing!

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