# How much salt/other product add to water so a medium acorn floats?

MarcBergmansAs
I have a lot of acorns in my pebbles.
I'm looking for a way to sort these out quickly.
I was thinking of the possibility that something floats on water and another material does not.
If I use plain water, most of these acorns will sink too.
So my questions is how much salt or other product should I add to 1 liter of water so that a medium sized acorn floats on it.

Thank You in advance

## Answers and Replies

Gold Member
Hi and welcome to PF. As you haven't specified the density of the most dense acorns then it's impossible to say. That means you would need to do some experiments (I doubt you would find that information on the WWW). The most suitable experiment would be to use a salt solution in which you add more and more (measured amounts of) salt until the heaviest acorn you have starts to float.

Experimental detail: there will be a significant volume of gases inside the acorns, which will gradually leave as water soaks into them, This will affect their overall density. They may even out-gas if they are about to sprout. So have a large number of acorns and take them out / dry them off .

Once you have found the minimum amount of salt for floating them all, you can look at your records to find how much salt you added.

russ_watters
Richard R Richard
Most dense wet woods have a density less than ##1250 kg/m^3##
Less dense natural stones ##2400 kg/m^3##
Therefore a saline solution with intermediate density can buoyancy separate acorns from pebbles.
Wet acorns are not comparable to the densest woods.
The variation in density of saline solutions is linear with the increases in salinity, the saturation of salt in the water occurs after 35% by weight or approximately 350 g per liter, since the variation in the volume of the water to add salt does not affect too much to calculate, so densities of ##1300kg/m^3## are easily achieved, the temperature does not alter the results if you use sodium chloride.
For economic reasons it is better to experiment with dilutions of lower concentration ##200g/l## seems a good criterion
You could develop the following experiment
• In an empty container, place another container with a lid that closes it at the root, without modifying its capacity, fill the internal container with tap water, until one more drop overflows it and spills,
• Weigh about 100 acorns or any other quantity, put the acorns in the container, the water will spill, put the lid on allowing all the acorns to sink into the water
• Remove the container and weigh the spilled water,(discounts the weight of the container), the weight ratio of acorns to weight of water will give you an idea of the average density.
The saline solution should have a higher salt to water ratio than the previous ratio, so that you can achieve efficient separation.
$$(\dfrac {weight\,of\,acorns} {weight\,of\,spilled\,water} -1) \cdot 1000 <x$$
## x ## = grams of salt per liter to dissolve
in case of negative, you could separate them with fresh water, or tap.

Lnewqban
Gold Member
The possibilities are endless. You could
• water the whole thing for a few months, then pluck the saplings out by hand,
• put shovelsful in your oven at 500F and the acorns would burn off, leaving only pebbles,
• let loose an army of squirrels to collect the acorn and stash them in the only available bolt hole in a tree, which has a back door for you to open and empty into the trash,
• study meteoromancy until you can summon a hurricane to whisk away the acorns, leaving only pebbles.

And I just realized I am making the huge assumption that it's the pebbles you're interested in preserving, not the acorns.

If it's the acorns you want to preserve, that's a whole nother kettle of worms.

...how much salt or other product should I add to 1 liter of water so that a medium sized acorn floats on it.
Consider the opposite approach:
Start with a litre of salt and keep adding water to it until the acorns sink.

phinds and sophiecentaur
Gold Member
Remove the container and weigh the spilled water
There is huge inaccuracy in actually identifying the 'spilled water'. Surface tension will make it nigh on impossible to say when the can is properly full (not over- full) of water. Also, when the water spills over, some of it will wet the sides and that's lost.
A Eureka Can (relic of my 1950s School `Science) is a bit better than an open can but water still sticks in the spout. My Physics Master was very down on the method!
Weight measurement is potentially much more accurate and the density of a large volume of salt water will can easily be found , using a decent kitchen scales to find the mass of added salt.

But, in any case, the OP wants to separate acorns from stones so that involves some sort of implied measurement and, once you have your salt solution that works, you can use it for the next lot and the next.

Slightly less invasive on the acorns could be to do it 'dry'. Using a leaf blower and dropping a mixture past the nozzle will separate the acorns from similar sized pebbles without getting them wet. A pre- and post filter with two suitable sized sieves will further increase the accuracy.

Alternatively, once all the wrong sized stones were eliminated, the mixture could be agitated until the stones fall to the bottom. (Another dry [= better] method)

As this is a real Engineering Problem, it would be necessary to specify the sort of accuracy needed -( i.e how many lost acorns) would be acceptable.

Richard R Richard
Hello @sophiecentaur , I agree with you, I have been very rudimentary in my method, but great precision is not necessary either, to be sure of the separation efficiency the percentage of salt in solution is increased and the problem is solved, the idea was that Look for a home method to determine the density of acorns, to establish a minimum concentration of salt in solution.
Suppose that salt is an expensive resource, then we should try to limit its use, although in reality for me the disadvantage of the method is that the separation method probably leaves traces of salt in the product and has at the exit of the separation only inedible salty acorns.
So at least after the separation a washing would come, to try to remove the salt from the surface of the acorn.

Gold Member
So at least after the separation a washing would come, to try to remove the salt from the surface of the acorn.
I agree with you too. The recipients may or may not be too fussy. However, I think you could consider the 'dry' alternative. No salt costs involved as long as you have a 'leaf-blower' or equivalent and a sieve / netting etc to do initial size selection. From your question, I suspect you are an owner of animals (or at least a friend) so my 'out-door based suggestions might be worth considering and practical for you.

Lucky pigs / deer / unspecified cuddly animals.

Gold Member
A few things I still think are unanswered yet crucial to finding valid solutions:

1. What is the end product? (What needs to be preserved? What can be sacrificed?)
• An acorn-free pile of pebbles,
• A pebble-free pile of acorns,
• Two piles: one of acorns, one of pebbles.
(eg. are solutions that destroy the acorns viable?)

2. Is it a given that the acorns are not broken and are generally water resistant? (Otherwise, all your density and buoyancy ideas go out the window).

Last edited:
sophiecentaur and Ibix