>My only problem is diluting the 90% formic down to>50% using a hydrometer...
>... Does anyone have a simple dilution table for formic dilution?  

I recall that one litre of formic added to one litre of water yields one litre
of the diluted acid.  There is little observable heat or bubbling and it is
like adding water to water, not at all like diluting nitric acid.

A decade or so ago, I collected some info on formic and presented it at
http://www.honeybeeworld.com/formic/default.htm  

Many of those links may be dead by now, but there are links to pictures
of our crew preparing formic pads at
http://www.honeybeeworld.com/diary/2000/diary101000.htm#Formic
and other useful material.

Since there are no significant volume changes, no table is needed.  
Dilutions can be predicted with sufficient accuracy using simple math.

Working with formic is best done outdoors the cool of early morning and
a light breeze.

Water buckets should be nearby as well as baking soda to neutralize
any acid that is spilled.  The water should be coloured with a few drops
of food colouring since formic looks just like water and, in  a panic could
be mistakenly used for flushing a spill.

Short-term contact with the acid is not painful unless it reaches an open cut or
sensitive areas like the eyes.  The eyes need protection and splash-proof
googles are recommended when handling the acid or acid-soaked pads.

Dipping hands into the acid, then washing immediately with water does
not seem to be harmful.  Having acid leak into gloves and sit on skin is
will result in serious burns if not discovered within minutes, so wearing
gloves is not advisable IMO.

If carried in vehicles, it should be carried separate from passengers and
in containers which are not prone to leakage or spilling.

In handling, the fumes can be quite overpowering.  I doubt that anyone
is likely to willingly breathe fumes strong enough to do damage, but
it is possible to get an accidental whiff that is most unpleasant if
precautions are not taken.

Some use chemical masks and that is probably wise and even mandatory
on some cases, but we never did.

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