[Czerczer (OP)]

Hello all! I am starting to research into various types of distillation, and am curious about a few things. How would I go about figuring out what my glassware can handle as far as negative pressure goes? I am also curious as to figure out how low I can get the boiling point of H2o with my current pump (Welch 1400) Any help pointing me in the right direction is highly appreciated!

[Kryptid]

If you know how good of a vacuum the pump can pull, you can use a phase diagram to determine what the boiling point of water will be at that pressure: http://www1.lsbu.ac.uk/water/water_phase_diagram.html

The lowest you can make the boiling point of water would be 0.01 degrees Celsius at a pressure of 0.006 atmospheres. Below that pressure, you can no longer have liquid water. Instead, ice sublimes directly into water vapor.

[chiralSPO]

As far as the glassware goes:

Low pressures are less risky than high pressures (one can never be more than 1 atm less than ambient), but you still really don't want to implode your glassware!

I recommend using thick-walled borosilicate glass (standard laboratory glassware should be fine). This will hold up well to the pressure difference across the glass, and will also be fine with sudden changes in temperature (not that vacuum distillation is likely to involved that, but be aware that once you start evaporating, it's going to cool down very quickly!)

The primary concern is whether the glassware has any defects that would lead to failure (keep a constant lookout--any minor chips or star fractures, and you should replace the piece (unless you have the equipment and knowledge to repair it).

For maximal safety, you can get glassware that has a polymer coating around the outside that will keep glass shards and dust from going everywhere if a failure should occur. (But this stuff is expensive!)

[Bored chemist]

(standard laboratory glassware should be fine).

Not reliably.
In particular, flat bottomed flasks are not usually safe under vacuum.
(Filtration flasks are made of heavy walled glass)

[evan_au]

A spherical flask will be stronger than a flat-bottom flask.
A cylindrical tube will be stronger than a square tube of the same thickness...

[chiralSPO]

(standard laboratory glassware should be fine).

Not reliably.
In particular, flat bottomed flasks are not usually safe under vacuum.
(Filtration flasks are made of heavy walled glass)

I guess I have been working in a specialized lab too long... I can't remember the last time I used a flat-bottomed flask...

Bored chemist and evan are correct. By "standard laboratory glassware," I meant spherical flasks with ground glass joints, and cylindrical tubes (or combinations thereof; also with ground glass joints).

Something along these lines: https://www.ebay.com/p/Glass-Short-Path-Distillation-Kit-With-Cold-Trap-and-Magnetic-Heating-Mantle-200/3016569763?iid=273446265460&chn=ps

[Bored chemist]

Incidentally, to get back to the OP's question; in science (rather than engineering) there's no such thing as a negative pressure.

[jeffreyH]

The above can also be said for negative energy.

[Czerczer (OP)]

Thanks for all the responses! I need to work on my vocab ha...

[chiralSPO]

Regarding negative pressures (and energies)

These depend a lot on how things are defined. Pressure is force/area, so it can have a negative value if one considers the direction of an absolute force, or if one is considering a net force (as is likely the case here: atmospheric pressure pushing in, and less than atmospheric pressure pushing out results in negative net outward pressure)

Also, as far as energy goes: potential energy can certainly be negative (it is usually set with respect to a relative 0). Convention often has gravitational potential energy 0 at infinity, which means that all gravitational potential energy is negative!