Question about Cyanide Gas (for a good cause :-)

Well, I'm still messing with the plot for the Harrison Chapters. It
seems that just when you get going, you slam into some sort of
technical problem. Recently, I sent questions to the TML about
tiny nukes, effects of vacuum on the unprotected. This time I'm
wondering about cyanide gas (I hope the TML-chemists aren't
jumpy tonight).

Here's what I've gleaned so far.

You take NaCN (Sodium Cyanide), mix it with some HCl (Hydrochloric
acid), and whammo, lots of HCN (Hydrogen Cyanide gas). I means lots.
Enough to really ruin everybody's day assuming you're on a
closed air supply (like a starship). Say one bucket of
ingredients per 10,000 tons of displacement affected?

Basically, I need know two things. First, is the above
description correct? Will just mixing the two make HCN and
will it really be a gas (ain't much  good as a liquid)?
And is it really as potent as I'm pretending (one bucket to
10,000 tons seems a little steep, maybe it's just me)?

Second, what does NaCN and HCN look like, smell like, etc? Well,
I guess not many people know what HCN smells like... :-) but you
get the idea. I need lots of adjectives for the story, and I don't
mean the sort you'd find reading an encyclopedia. Anybody
have an ounce of hands-on experience with this sort of
thing? (Don't say anthing self-incriminating, now :-)

Many many many thanks in advance.

[email removed]

PS: If anybody wants the story (to date) emailed to them,
let me know privately. It's too much to put on a mailing list.