Boiling Points

Everyone has boiled water at some point so everyone has a basic understanding of what is meant by boiling. We put a pot on the stove, go away for ten minutes, and come back to find the water boiling vigorously, ready for the pasta, eggs, or oatmeal to be put in.

To really watch what happens with water we must have a thermometer and some patience. When we put cool tap water into a beaker and place this on the stove and turn on the heat we may see ripples in the water as the water heats. These ripples are called Schleeren patterns and arise from light being diffracted off of the regions of water with different temperatures and hence different densities. This is exactly the same optical effect that gives rise to mirages. Since the water is being heated from below, the lighter, warm water will rise in the beaker causing cooler surface water to flow to the bottom.

At some temperature, usually around 80 oC, small bubbles will be observed on the inner surface of the beaker. Many people confuse this with boiling. These bubbles are the air that was dissolved in the water at room temperature coming out of solution. Air becomes less soluble in water as the temperature goes up.

If we continue to heat the water we will begin to observe bubbles form and collapse on the bottom of the beaker. These are the precursors to true boiling. The water on the bottom surface of the beaker is heated to the point where it converts to vapor, but this vapor cools rapidly as it expands and as it encounters slightly cooler water just above the bottom of the beaker. As the bulk water in the beaker becomes hot the bubbles begin to break free of the bottom and rise. Only when the water in the beaker is uniformly hot will the bubbles rise from the bottom and break free at the top. This is often called a rolling boil and is the point of true boiling. The phenomenological definition of boiling is the existance of sustained bubbles that break free of the surface.

Let's look more closely at this process. The bubbles that form at the boiling point contain water vapor. In order for a bubble to exist the pressure of the vapor in the bubble must be pushing against the water with exactly the same force that the water is pushing back. Assuming that we have a normal beaker and just a few cm of water, almost all of the pressure being exerted by the water is air pressure. Hence for the bubble to exist the vapor pressure must be equal to atmospheric pressure. We define a "normal" boiling point as the boiling point of the liquid at 1 atm, or another way of saying this is that the "normal" boiling point is the temperature at which the liquid's vapor pressure is equal to 1 atm.

In previous notes we have established that vapor pressure is determined by both temperature and by intermolecular forces, it should be no surprise that the "normal" boiling point will reflect the intermolecular forces of the liquid.

Does "Boiling" Mean "Hot"?

If boiling occurs when the vapor pressure inside the bubble equals atmospheric pressure, what would happen if the atmospheric pressure would drop? The simple example of this is the case of a camper who is on the top of a 10,000 ft mountain. While water boils at 100 degrees C at sea level (where the atmospheric pressure is 760mm Hg) the atmospheric pressure at 10,000 ft altitude is about 530 mm Hg. Because the boiling point of water is about 90 degrees C at this altitude., not only will our camper find that his food will cook a little slower than normal, any attempt to boil water to kill germs and pathogens may be unsuccessful since the water isn't getting hot enough.
In fact, water will actually boil at room temperature if you apply a vacuum of around 5 torr to the vessel holding the water!

The above information was gleaned from

SO what does all of this have to do with herbs?

Tinctures are made with solvents, and some herbs are better extracted with solvents, either because steam distillation simply doesn't work, or often times as in Jasmine or Roses, steam temperature (100c) destroys the fragrence.
Most of the time the solvent will be ethanol (drinkable alcohol) but sometimes the solvent used will be someting more toxic, and you'd like to remove it after the extraction process, or perhaps you simply want to concentrate your tincture that you've just made. Either way, boiling the solvent off is a good way to get rid of it, as long as the boiling temperature of the solvent won't hurt your product.

When you are distilling (boiling) things, you can tell what solvent is currently boiling away in your setup, by watching a thermometer that is placed in the vapor of the boiling substance, because each solvent has a unique boiling temperature at sea level.

For example, (at sea level) if it's ethanol (alcohol) that you're boiling off, the vapors will be at 78 degrees C..... if it's water you're boiling off, the vapors will be at 100 degrees C

Now I chose these two solvents (yup, water is a solvent, and a great one at that!) because in the case where they are mixed, a funny thing happens... water and ethanol in particular form something called an azetropic mixture (also known as a constant-boiling mixture) which in simple terms means that the alcohol cannot be separated from the water somewhere around 95% pure ethanol, the mere act of boiling won't remove any more water. That's why you find "Everclear" at a maximum purity of 190 proof, or 95%, because it's impossible to remove any more of the water from it using distillation!!

So when you boil off a mixture of alcohol and water, expect temperatures somewhat different than the individual components alcohol mixed with water will boil at closer to 88-90 degrees C, and depending on the ratio of alcohol and water, the boiling point can be anywhere between 80 and 100 degrees c!!

When you are boiling things at higher altitudes than sea level, just like water, the actual boiling temperatures of solvents will be less than they are at sea level!!!
There are charts and nomographs that you can use to find the corrected boiling temperatures of solvents for your altitude

SO when your thermometer just WON'T go as high as you think it ought to, take a moment and remember that if you live in the mountains, you shouldn't toss your thermometer in the trash, because it's doing it's job perfectly!!

Here are the boiling points of some common solvents used in chemistry:
Consider them all toxic- but the ones labelled "toxic" are REALLY nasty...
DO NOT consider using any of these solvents (but water) in your distillation set unless you are familiar with them and what they can do.
Most are poisionous and very dangerous!!
This information is provided only as a matter of interest !

ACETONE (dimethyl ketone, ketone propanone, propanone)
bp 56.48 C

BENZENE (C6H6, benzol, phenyl hydride, coal naptha) (included for comparison and wouldn't want it anywhere near yourself)
bp 80.1 C,
TOXIC: 3000 ppm vapor considered high concentration, toxic via inhalation or skin absorption as well as oral ingestion, prolonged inhalation of low concentrations also toxic
NOTE: do not confuse with benzine which is a petroleum distillate
Caution: TOXIC: Benzene is a recognized leukemogen (causes leukemia)!

BUTANE (C4H10, n-butane, methylethyl methane, butyl hydride)
bp -0.5 C

CHLOROFORM (CHCL3, trichloromethane)
bp 62.26 C,

DICHLOROMETHANE see methylene chloride

bp aprox 174 C

DIETHYL ETHER (C2H5-O-C2H5, ether, ethyl ether, anesthesia ether, ethyl oxide)
bp 35 C

ETHYL ALCOHOL (ethanol, methyl corbinol, spirit of wine, grain alcohol, Everclear, 95%)
bp 78.32 C,
Drinkable but don't drive after drinking!!

DENATURED ALCOHOL This is Ethanol that has a nasty substance added to it to make it unfit for human consumption, usually toxic.
There have been reports of people using denatured alcohol as a solvent.
NOT a good idea if the result is for human or animal use.
May be ok if it is denatured only with something that will be completly eliminated when the solvent is boiled off (e.g. with methyl alcohol).
If you don't ABSOUTELY know that you can eliminate the denaturant 100%, then NEVER use denatured alcohol for herbal preparations!
Results varying from death to permanent blindness may and probably will result!

bp 175-325

bp aprox 98 C

bp aprox 69 C

ISOPROPYL ALCOHOL (dimethyl alcohol, sec-propyl alcohol, isopropanol)
bp 80.3 C,

METHYL ALCOHOL (methanol, wood alcohol)
bp 64.8 C,
TOXIC !! death to blindness can result from it's ingestion!

METHYLENE CHLORIDE (CH2Cl2, dichloromethane)
bp 39.8

NAPTHA, V.M. & P. (benzine, 76 degree naptha)
bp 100-140 C, AKA lighter fluid

bp 138-165 C,

NONANE (C9H20, n-nonane)
bp aprox 151 C

bp aprox 126 C

PENTANE (C5H12, n-pentane)
bp aprox 36 C

PETROLEUM SPIRITS (petroleum benzine, petroleum naptha, light ligroin, petroleum ether, mineral spirits)
bp 35-180 C,

alpha-TRICHLOROETHANE (CH3CCl3, 1,1,1-trichloroethane, methyl chloroform)
bp 74.1 C,

TOLUENE (C6H5CH3, methylbenzene, phenylmethane, toluol)
bp 110.4 C

TURPENTINE (spirit of turpentine, turpentine gum, turpentine oil)
bp 154-170 C

bp 100 C (212 F)
An amazing solvent that you can actually drink!

(m-xylene) bp 139 C
(o-xylene) bp 144.4 C
(p-xylene) bp 138.3 C