Specific Gravity Conundrum?

[Red Letour]

I had a vintage lamp working nicely on the suggested Epsom salt mixture, but wanted to see if going to a propylene glycol mix instead would give the lava a better motion. So I foolishly bought a small refractometer and measure the specific gravity of the working solution, which was about 1.033. I figured that if I started with the new mix at a similar point, the lava would cycle similarly.

Nope.

The glycol mix wouldn't float the lava at all, at that same specific gravity. And right now it is barely teasing the lava, with the s.g. somewhere way above 1.06, which is the top of my scale.

So, I'm confused. How can the lava not float, in a fluid which has a higher s.g. and is 'thicker' than the last fluid it was floating in?? I thought the whole game was about relative density, and if that was the same, the floating should be the same.

What am I missing here??

(And yes, if I do kick it up high enough, the lava will float, and it does "ooze" better.)

[Tim Gill]

What exactly are you using in the lamp to change the densty of the water - PG and epson salts or just PG

Also I am assuming you are using surf as no surf and this will not brake the wax up enough to allow it to flow

i do have experience with both PG and salts but i do not use a refractometer or similar - i just add, take out and aggust as required until the flow is how I like it.

[Red Letour]

Tim-

 Just distilled water & PG this time around. I did add a very small amount of surfactant tonight, after observing the way that "just a drop" can turn a hot lamp into a swarm of bees in a prior (Epsom salt) fill. Tonight it was one drop of liquid hand soap diluted into 10ml of water, and then about 1/2 ml of the diluted surfactant as a start. (Yes, I plan to cautiously add a bit more.)

Had two lamps, both Epsom salt fills, tired surfactant in one but not the other. The one with no surfactant at all is the one I was comparing sg with, and that had no flow problems. The one with one drop of Dawn became a bee hive when it got really hot, which is how I know it can work without any surfactant, and "should" already be working at the same sg, even without surfactant.

[Tim Gill]

How has the lamp with very little surf in it worked out, you could probably sort the other out by dumping the water and redoing it again if its annoying you enough.

It is interesting though as i have not had the same issues - I use dawn or most of the time or the gookit surf which is less strong then dawn the gookit is better as you can control it more as you have to use more of it then where as dawn it has to be no more then 1-2 drops.

[Red Letour]

If the surfactant was the only problem with the glycol mix, after some time a huge glob of wax would still rise up. Instead, most of it stays at the bottom and what does rise, doesn't quite hit the top or stay there for any length of time, it just cycles back down again.

There is something wrong and I'd have to guess the wax just isn't buoyant in the water/pg mix. I'm tempted to add some Epsom salt water to see what that does.

[Tim Gill]

It could also be that its not getting hot enough, if it is though then adding some more PG to make the wax float all the way to the top would be a good idea.

[Red Letour]

Could certainly be, but it was hot enough to make the cycle work before I changed the fluid. I can swap out the base for another one that is working and make sure. It would nice nice if it was that simple.<G>

I did change the socket and bulb in a gen-you-whine Mathmos TelStar so I could "adjust" the heat by changing the bulb. There's a wide variety of bi-pin bulbs available (25-30-35-40 etc. watt) as opposed to the unobtainable 30W minispots they specify for it. The 25W minispots that are on the US market, just don't cut it.