[Byrne]

How is it that BaSO4, a poisonous substance, can be used as a dye in gastrointestinal x-rays?

[Mitch]

I assume this is some sort of radioactive tracer?

[Borek]

pKsp = 10.0

[Borek]

No, it is used as a 'shadow'. You have to drink large amount of slurry.

[Byrne]

I'm not sure I understand these responses...

[Borek]

Think about solubility.

[Byrne]

Think about solubility.

So, since BaSO4 is actually dissolved in solution, its not poisonous even though Ba(s) is poisonous?

[limpet chicken]

Soluable salts of barium are highly toxic, but BaSO4, is very, VERY insoluable, it is about as soluable in water, as PbSO4 is soluable in dilute sulfuric acid, maybe less so, so in other words, you are recieving maybe a few mg/mcg of Ba, if that.

It is used for gastrointestinal x-rays, both by enema (shudders) or orally, as it effectively shows up the soft tissue.

I shudder to think of when its swallowed, what comes out the other end

[jdurg]

Soluable salts of barium are highly toxic, but BaSO4, is very, VERY insoluable, it is about as soluable in water, as PbSO4 is soluable in dilute sulfuric acid, maybe less so, so in other words, you are recieving maybe a few mg/mcg of Ba, if that.

It is used for gastrointestinal x-rays, both by enema (shudders) or orally, as it effectively shows up the soft tissue.

I shudder to think of when its swallowed, what comes out the other end

On the bright side, after ingesting a barium smoothie, if you could get your flatulence to ignite it may wind up having a bright green color to it.  

[limpet chicken]

I have only ever once managed to actually ignite my flatulence "as it comes", using a mapp-gas torch lighte I picked up on holiday

I have managed to fart into a bottle and ignite that though hehehe.

Jdurg, I really doubt it would color the flame though, as there would be no solid barium particulates expelled, and unless there is some obscure, gaseous compound of Ba produced by intestinal flora, then there is going to be no volatile Ba to color the offensive eruption in question.

[Albert]

...and did you know that BaSO4 is soluble only in H2SO4 conc.?

BaSO4 + H2SO4 -> Ba(HSO4)2

When my professor showed me this reaction I was taken aback.

[Alberto_Kravina]

...and did you know that BaSO4 is soluble only in H2SO4 conc.?
BaSO4 + H2SO4 -> Ba(HSO4)2

It is soluble in hot concentrated sulfuric acid (I made the reaction by myself in the lab but the BaSO₄ always precipitated when I cooled down the solution.

By the way: solubility of BaSO₄ in water is about 2.3 mg/L

[Borek]

Once you know that pK_a2=1.99 for H₂SO₄ thats nothing strange.

Alberto: solubility given in mg/L is much less usefull than Ksp information which I gave earlier

[jdurg]

I have only ever once managed to actually ignite my flatulence "as it comes", using a mapp-gas torch lighte I picked up on holiday

I have managed to fart into a bottle and ignite that though hehehe.

Jdurg, I really doubt it would color the flame though, as there would be no solid barium particulates expelled, and unless there is some obscure, gaseous compound of Ba produced by intestinal flora, then there is going to be no volatile Ba to color the offensive eruption in question.

All you need is particulate matter in your flatulence for the effect to be seen.  (It's like throwing a powder of a salt into a flame).  So if your flatulence contains any particulate matter with some of the BaSO4 stuck to it, then it is possible for a color to be seen.  (And as gross as it is to believe, there is a great deal of particulate matter in flatulence).

[Alberto_Kravina]

Jdurg, I really doubt it would color the flame though

A good advice: add some potassium chlorate to the insoluble BaSO₄ and add HCl_conc., after that you'll be able to see the green Barium color. This is a trick to Identify cations with flame tests in insoluble samples without dissolving them.
The only disadvantage: K⁺ has also a flame color, so maybe it might be a bit difficult to distinguish all cations that are in the sample.