# Hoke-isms



## badastro (Sep 10, 2007)

I thought I'd share something.

Hoke describes sulfur dioxide as having "an extremely evil smell" haha :lol: 

It is quite evil. There are few things that have that strangling choking smell. After working with SMB, I know what sufur dioxide smells like and I can even smell it in preserved fruits like apricots. Disgusting


----------



## lazersteve (Sep 10, 2007)

Astro you are right about this one,

The only smells that I dislike more is a run off between hot ammonia or nitrous oxide fumes. I guess they are so vile to keep us from breathing them!!!! :lol: :lol: I get the willies everytime I work with nitric acid. One day I hope to have a process that requires zero nitric acid. Even with a good fume hood and or my respirator I don't like the stuff.

Chlorine runs a close third for me.


Steve


----------



## badastro (Sep 10, 2007)

Hoke mentions precipitating platinum before gold in mixed solutions. Is this advisable?

She also says to dilute the solution with several volumes of water before precipitating platinum with ammonium chloride. This goes against what others have said about using only concentrated solutions. Who's right?


----------



## lazersteve (Sep 10, 2007)

Astro,

I've only precipitated very small amounts of platinum from solutions which did not contain dissolved gold. In these instances I could not get precipitation from dilute solutions. The water solubility of the resultant salt almost dictates the solution must be concentrated. Can you give a page number of the Hoke book for reference so I can look it up? 

Harold would be the best member to answer this one in my opinon.

As for gold precipitations, if the solution is concentrated the gold will literally plate out onto the vessel when the SMB is added. For this reason I always dilute my auric chloride 2-3 times over with water before adding SMB.

Steve


----------



## Harold_V (Sep 10, 2007)

lazersteve said:


> Harold would be the best member to answer this one in my opinon.



Real simple. Platinum and palladium refuse to precipitate from dilute solutions. Keep them as highly concentrated as is possible for the best results. Someplace in Hoke's book you should read a statement to that effect. It's been years, so my memory has dimmed. 

This is something you can prove for yourself. Dissolve a small amount of platinum, then split it in halves after filtering. Leave one half well concentrated, then dilute the other by several volumes. Introduce ammonium chloride and tell me which one works best. 



> As for gold precipitations, if the solution is concentrated the gold will literally plate out onto the vessel when the SMB is added. For this reason I always dilute my auric chloride 2-3 times over with water before adding SMB.
> Steve



That doesn't often occur if the vessel is very clean, although I have seen the entire surface covered as if it was plated. After precipitation, a sheet would peel off the surface, aided by a plastic policeman. 

My solutions were heavily concentrated when I re-refined---I started with about a liter of gold chloride that contained roughly 17-19 ounces, then added enough ice to the 4,000 ml cylinder to bring it near the top. SO2 was then percolated through the solution, with the gold precipitating progressively. When the operation was finished, the 4 liters of solution were quite warm, and the gold was down. 

I think if you use this bit of logic, you'll know which metal should be precipitated first. It all revolves around drag down, and your ability, or lack thereof, to wash the precipitant.  

Gold powder can be washed endlessly, so you can, for all practical purpose, eliminate drag-down of other elements. That isn't true for the platinum group, which is precipitated as a salt-------which is very soluble in water. Washing the salts is not easy without dissolving them. I strongly advise that gold be precipitated before platinum------and considering that the process for palladium begins with ammonium chloride, platinum will come next, with palladium being last. 

Harold


----------



## Noxx (Sep 11, 2007)

Yes Chlorine and SO2 are the worst (for me) I have the impression that the smell stay even after exposure... Very annoying. 

And when I eat apricots, I know that I'm eating SMB at the same time... Should not be so good for the health lol.


----------

