Contributed by: Jim Webb <jnw4347@email.unc.edu>
A container filled with clear or dyed liquid contains a non-water-soluble substance (the "lava") that's just a little bit denser (heavier), and has a greater thermal coefficient of expansion, than the liquid around it. Thus, it settles to the bottom of the container. A heat source at the bottom of the container warms the substance, making it expand and become less dense than the liquid around it. Thus, it rises. As it moves away from the heat source, it cools, contracts a bit, and becomes (once again) heavier than the medium. Thus, it falls. Heavy, light, heavy, light. Sounds like a Milan Kundera novel. (Actually, to be more precise: dense, less dense, dense, less dense.)
Contributed by: Jim Webb <jnw4347@email.unc.edu>
Use mineral oil as the lava. Use 90% isopropyl alcohol (which most drugstores can easily order) and 70% isopropyl alcohol (grocery-store rubbing alcohol) for the other ingredient. In 90% alcohol the mineral oil will sink to the bottom; slowly add the 70% alcohol (gently mixing all the while; take your time) until the oil seems lighter and is about to "jump" off the bottom. Use the two alcohols to adjust the responsiveness of the "lava."
This mixture is placed in a closed container (the "lava lamp shape" is not required, although something fairly tall is good) and situated over a 40-watt bulb. If the "lava" tends to collect at the top, try putting a dimmer on the bulb, or a fan at the top of the container.
To dye the lava, use an oil-based dye like artists' oil paints or a chopped-up sharpie marker. To dye the liquid around it, use food coloring.
Two suggestions for better performance: 1) Agitation will tend to make the mineral oil form small bubbles unlike the large blobs we're all used to. The addition of a hydrophobic solvent to the mixture will help the lava coalesce. Turpentine and other paint solvents work well. To make sure what you use is hydrophobic, put some on your hand (if it's so toxic you can't put it on your hand, do you want to put it in a container that could break all over your room/desk/office?) and run a little water on it. If the water beads, it should work fine. 2) For faster warm-up time, add some antifreeze or (I've not tried it) liquid soap. Too much will cloud the alcohol. Keep in mind that the addition of these chemicals may necessitate your readjusting the 90% to 70% alcohol mixture.
The patent itself is not very specific as to proportions of ingredients. The solid component (i.e., the waxy-looking stuff that bubbles) is said to consist of "a mineral oil such as Ondina 17 (R.T.M.) with a light paraffin, carbon tetrachloride, a dye and paraffin wax."
The medium this waxy stuff moves in is roughly 70/30% (by volume) water and a liquid which will raise the coefficient of cubic thermal expansion, and generally make the whole thing work better. The patent recommends propylene glycol for this; however, glycerol, ethylene glycol, and polyethylene glycol (aka PEG) are also mentioned as being sufficient.
This mixture is placed in a closed container (the "lava lamp shape" is not required, although something fairly tall is good) and situated over a 40-watt bulb. If the "lava" tends to collect at the top, try putting a dimmer on the bulb, or a fan at the top of the container.
Several non-water-soluble chemicals fall under the category of being "just a little bit heavier" than water, and are still viscous enough to form bubbles, not be terribly poisonous, and have a great enough coefficient of expansion. Among them: Benzyl alcohol (Specific Gravity 1.043 g/cm3), Cinnamyl Alcohol (SG 1.04), Diethyl phthalate (SG 1.121) and Ethyl Salicylate (SG 1.13). [The specific gravity of distilled water is 1.000.]
Hubscher recommends using Benzyl Alcohol, which is used in the manufacture of perfume and (in one of its forms) as a food additive. It can be obtained from chemical or laboratory supply houses (check your yellow pages); the cheapest I could find it for was $25 for 500 ml (probably 2, maybe 3 regular-sized lava lamps' worth). An oil-soluble dye is nice to color the "lava"; Hubscher soaked the benzyl in a chopped up red felt-tip pen and said it worked great. [Benzyl alcohol is "relatively harmless", but don't drink it, and avoid touching & breathing it.]
Hubscher found that the benzyl and the water alone didn't do much, so he raised the specific gravity of the water a little bit by adding table salt. A 4.8% salt solution (put 48 grams of salt in a container and fill it up to one liter with water) has a specific gravity of about 1.032, closer to benzyl's 1.043. I find that the salt tends to cloud the water a bit. You might want to experiment with other additives. (Antifreeze? Vinegar? Glycerin?)
This is put into a closed container and placed above a 40-watt bulb, as above. Either way, I would suggest using distilled water and consider sterilizing the container by immersing it in boiling water for a few minutes.. algae growing in lava lamps is not very hip.