[jeffreyH (OP)]

As helium is heavier than hydrogen would the liquid forms separate and if so which would be on top?

[CliffordK]

My guess is that the two would be reasonably non-polar, so they would likely mix, but it may take some mixing or shaking.

The density of liquid helium is 125 grams per liter.
The density of liquid hydrogen is 70 grams per liter.

So, at least initially, the hydrogen would layer above the helium.

[jeffreyH (OP)]

My guess is that the two would be reasonably non-polar, so they would likely mix, but it may take some mixing or shaking.

The density of liquid helium is 125 grams per liter.
The density of liquid hydrogen is 70 grams per liter.

So, at least initially, the hydrogen would layer above the helium.

The reason I asked was because of the work of Kamerlingh Onnes. Especially as shown here;

http://iopscience.iop.org/0953-8984/21/16/164222

This is counter-intuitive as are the properties of helium as a Bose-Einstein Condensate when expressed as a superfluid.

[CliffordK]

The reason I asked was because of the work of Kamerlingh Onnes. Especially as shown here;
http://iopscience.iop.org/0953-8984/21/16/164222
This is counter-intuitive as are the properties of helium as a Bose-Einstein Condensate when expressed as a superfluid.

From the abstract:

the helium-rich vapour phase sank to the bottom, having become heavier than the hydrogen-rich liquid phase.

So, at around the BP of Hydrogen (-252.9° 20.25K), the Helium should be a gas (BP -268.9°C, 4.25K), they found that the liquid hydrogen formed a layer above the gaseous helium.

Since the density of liquid helium is about twice that of liquid hydrogen, apparently the super cooled gaseous helium is at such a high density (relatively speaking) that it is also greater than hydrogen.

At below the BP of Helium (at 1 ATM), say 4K, one would also expect the helium to form a layer below the hydrogen.

Found this abstract:

The solubility of helium in liquid hydrogen has been measured as a function of temperature and pressure. It was found the solubility varied from 0.59 mole % for T=26.8°K and 1.98 atm partial pressure of helium to 11.1 mole % for T=19.8°K and 7.0 atm partial pressure of helium.

This seems to be measured at high pressures, and at temperatures above the 1ATM BP of helium and/or hydrogen, but they are not being listed as miscible, although 11 mole percent is quite high.

This may be temperature dependent as apparently around 0.9K, ³He and ⁴He undergo a fluid/superfluid separation and form distinct layers.

[jeffreyH (OP)]

Thanks for the info. I think the liquid helium would settle below the liquid hydrogen. Simply because of the recorded density differences.

[CliffordK]

Ahhh...  I think I found the answer.

YOU CAN'T!!!  (at least at pressures near 1 ATM).

I was focusing too much on the BP.  One should also consider the MP.

Hydrogen:

Boiling point    20.271 K, -252.879 °C, -423.182 °F
Melting point    13.99 K, -259.16 °C, -434.49 °F
Triple point    13.8033 K, 7.041 kPa

Helium:

Melting point    (at 2.5 MPa) 0.95 K, −272.20 °C, −457.96 °F
Boiling point    4.222 K, −268.928 °C, −452.070 °F
Triple point    2.177 K, 5.043 kPa

So, at 1ATM, 4K, Hydrogen is a SOLID, while the Helium is a liquid.

At higher temperatures, the helium is a gas, while the hydrogen is a solid.

So, now what one has is different phases:
14K to 20K, Helium is a gas, Hydrogen is a liquid.  Gaseous Helium is only partly soluble in liquid Hydrogen.

5K to 14K, Helium is still a gas, Hydrogen is a solid.  Obviously they wouldn't mix.  The cool thing is that if liquid hydrogen floats on gaseous helium, then solid hydrogen (density, 86 gm/cubic decimeter) may also float on gaseous helium.

1K to 4K, Helium is a liquid, Hydrogen is a solid.  Solid Hydrogen would float on liquid Helium.

< 1K, Helium is a superfluid.  Hydrogen is still a solid, and they still won't mix, the hydrogen should still float in the helium, but the helium should form a thin film over the top of the hydrogen block.

So, really, to run your experiment with liquids, you would have to run it at very high pressures.  Perhaps 100 ATM?  1000 ATM?  Based on the experiment cited above, I'd guess that at high pressures, one could achieve both liquid hydrogen and liquid helium, and since more helium gas dissolves in liquid hydrogen, the two may be close to miscible at pressures high enough to liquefy the helium (assuming the hydrogen remains a liquid).

Ahh, found some further reading (same article, second link should be direct to the PDF).
http://adsabs.harvard.edu/full/1977ApJS...35..221S
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1977ApJS...35..221S&defaultprint=YES&filetype=.pdf

Anyway, a lot of the discussion seems to be at relatively high temperatures, and very high pressures, but depending on the conditions, hydrogen and helium will either mix relatively well, or partly separate. 

[Soul Surfer]

The point of the paper was that the density of helium gas (not liquid) was great enough to sink in Liquid hydrogen.  This is plausible because of the very little attraction of helium atoms for each other and the incredibly low boiling point of Helium