Homebrew PCBs

Jeremy Taylor wrote:
> The biggest problem with phosphoric acid is it's low vapor pressure at room
> temperature,i.e. when heated it evaporates, vaporizes very readily. (faster
> than water)   This result in more irritating fumes than most other etches,
> and is probably the reason very few people use it as such.
> 

I always thought a substance of low vapor pressure would 
evaporate less than a substance of high vapor pressure. I can 
tell you concentrated phosphoric acid (80% wt) at room temp is 
orderless, even when taking a sniff from the bottle. The stuff is 
concentrated by evaporation so I don't know it can evaporate 
faster than water. Its also not extremely dangerous to spill on 
you. As a comparison I would say NaOH is a lot more corrosive you 
your skin than con. H3P04. It takes a few minutes to start 
feeling the pain, and I have sensitive skin.


Adam.