# If I pour seawater on my path, will it freeze?



## Just the One (8 Jan 2010)

Can anyone living by the sea do a test for me. 

Can you go get a bucket of sea water this evening, throw it on a path and see if it freezes. Also, leave some in the bucket and see if it freezes.

I am trying to find out if the salt content is high enough to resist freezing and/or will it disolve frozen paths.


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## addob (8 Jan 2010)

*Re: a test for those living by the sea*

There was ice yesterday morning on the beach in Sandycove if that helps answer your experiment.


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## messyleo (8 Jan 2010)

*Re: a test for those living by the sea*

I noticed the ice on the beach at sandycove today as well.


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## Brendan Burgess (8 Jan 2010)

*Re: a test for those living by the sea*



jaybird said:


> I live at the beach, but oddly enough I won't be on the shore this evening in the minus 7 temps with freezing fog collecting sea water to see if it freezes.



Great post  

When the roads are clear, I will drive down to Sandymount and get a bucket of water and check it out. 

Brendan


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## onq (8 Jan 2010)

I know it might sound utterly foolish, but is there some reason the Government needs to import grit and salt, when mixing sea sand and brine and spraying it on the road should surely do the trick?

Is there sone unusual reason we couldn't do this short term even, until we get in new stocks - 10 days lead-in apparently?

Surely there are tankers to spray the brine and we have plenty of trucks from which energetic lads with shovels could artistically strew the roads with crescents of sand?

Is this utterly off the wall or wha?

Mind you I have to say that it took two applications of salt and boiling water to clear my steps this morning at a mere -3 and Meath yesterday was -7.5

ONQ.


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## Damo (8 Jan 2010)

I'd love to know the answer to this. My 9 year old son came up last night with the idea of using sea water on the roads - shows a bit of lateral thinking at least!!


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## GarBow (8 Jan 2010)

Answer without the frostbite


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## Brendan Burgess (8 Jan 2010)

Sea water freezes at around -2 degrees,so it would make the problem worse.

http://www.waterencyclopedia.com/Re-St/Sea-Water-Freezing-of.html

Brendan


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## elcato (8 Jan 2010)

They actually used beach sand in the eightees for this. I cant be certain but I believe a mixture of sand and salt caused bad corrosion to vehicles and they may risk being sued by the SUV brigade if you catch my drift.


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## onq (8 Jan 2010)

Perhaps I'm missing this but let me get this straight:

The received wisdom is that:

i) Don't use sea water because it isn't salty enough

How salty does it need to be to actually help?
Everything was frozen solid north of the M50 yesterday when I was in Meath, including the approaches to the M50 interchange when travelling back at around 12.30pm.
Even the slip road right at the ronudabout had ice on it and it was definitely salted and gritted to a good level.
Salted and gritted roads were frozen at o degrees on Wyattville Estate in Killiney/Ballybrack as I went as far as the Cherrywood roundabout on Wednesday night to get a feel for the Meath trip.

What do people think happens to a salt spray when its spread on 24-50mm packed snow?
If it makes any impression at all it'll dissolve into it and I can hardly believe it'll stay much saltier than seawater.

ii) Don't use seashore sand because it will cause corrosion

There are two types of sand we were thought in our materials course.
Sea sand and river sand which is sharp-edged.
Desert sand which gets rounded by friction.

I'm presuming the grit we get is a mixture of sharp sand and stones.
Well, there are plenty of quarries in Ireland, and one guy was on the news last evening offering to sell the required stuff if the Council's wanted to buy.

So what is going on with this salt and grit thing?
Is is that they can't stand to see an Irish firm make a profit?
Do we have a secret understanding with the Eastern Bloc to buy their sand and gravel?

I'd just like to know.

Ta.

ONQ.


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## onq (8 Jan 2010)

elcato said:


> They actually used beach sand in the eightees for this. I cant be certain but I believe a mixture of sand and salt caused bad corrosion to vehicles and they may risk being sued by the SUV brigade if you catch my drift.



Surely it cannot be any worse than the mixture on the roads now?

Waitaminnit - the eighties, you say.

Sure most cars back then were rustbuckets anyway.

"They're all like that sir".



ONQ.


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## onq (8 Jan 2010)

http://www3.hants.gov.uk/roads/highway-information/winter-salting/road-salt.htm

*How Road Salt Works*

_Rock salt is used for treating roads, footways and cycletracks and although it has a gritty appearance it is not "grit". The salt works by lowering the freezing point of moisture on the road surface. Before salt can become effective, it needs to be crushed by the traffic and dissolve. It is less effective at temperatures below minus five degrees centigrade (-5°C) and has virtually no effect below -10°C. 
  The County Council uses wetted salt on its road network. This system uses brine which is sprayed onto dry salt as it is discharged from the vehicles. With this system the salt is a more effective deicing agent as it goes into solution faster and remains on the road surface longer than dry salt because it is not blown around by the wind.
  Less wetted salt needs to be used to give the same results which is of benefit to the environment.
  The white appearance of a well salted, dry road surface should not be mistaken for frost and it is normally safe for traffic movement. Often, even when dry, residual salt will itself attract moisture and can give the road surface a damp appearance, but the salt should prevent the moisture from freezing.
  There is no such thing as an absolutely safe road surface._
_The presence of salt will not always guarantee an ice-free surface so concentration and care is always necessary when driving in winter._


So there you go:

They even say they use brine  - unsure of the concentration relative to seaqate.
They say brine is MORE effective than dry salt which can be blown off the road surface.

I can confirm that from trying to scatter table salt on the path on Wednesday morning.
The salt blew all over the place - it went everywhere except for the path until the wind died down.
But you can imagine that when there's any wind, unless it melts in fairly quickly, it'll just end up at the sides of the road with all the slush and heaped snow where it'll do little good.

FWIW

ONQ.


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## cobalt (8 Jan 2010)

_Anything_ dissolved in water will depress its freezing point. The compound's efficacy at depressing the freezing point depends on a few things; generally, the lighter the molecule and the more it ionises (divides into smaller fragments) when it dissolves, the more effectively it will reduce the freezing point.
Sodium chloride is a pretty light molecule and it splits into two ions when it dissolves, so it's fairly good. 1% of sodium chloride reduces the freezing point by 0.576 degrees centigrade, and you can scale that relationship up/down, _i.e._
pure water (0% sodium chloride) freezes at 0 degrees C
1% solution of sodium chloride in water freezes at -0.576 degrees C
2% solution of sodium chloride in water freezes at -1.152 degrees C
0.5% solution of sodium chloride in water freezes at -0.288 degrees C
_etc._

So if the prevailing temperature outside is -7 degrees (for example), you will need more than 12.2% (calculated as 7/0.576) of sodium chloride dissolved in order to prevent water from freezing.

The other issue, of course, is getting the salt to dissolve! The lower the temperature, the more difficult that is. It's obviously easier to have salt as a preventive measure to stop water from freezing, rather than trying to treat water that's already frozen.

Assuming sea water has a typical salt concentration of 3.5%, it would freeze at just under -2 degrees centigrade (calculated as -0.576 x 3.5). But the sea would actually need to be even colder than that in order to freeze hard because the motion of the waves militates against freezing.
Here's seawater just on the point of freezing.

As I said, anything that dissolves in water can depress its freezing point, but they vary in how effective they are. For example, table sugar (sucrose) reduces water's freezing point by only 0.047 degrees for every 1% of sucrose. Therefore you'd need a theoretical concentration of 148% sucrose (which is obviously impossible!) to get water to stay liquid at -7 degrees.

Incidentally, just like dissolving anything in water lowers its freezing point, so too it raises its boiling point. That's why salt is added to water when cooking pasta _etc. _It's not just a flavour thing - it actually allows the liquid to reach a higher temperature. If you were just boiling food in plain water, it could only go to a maximum of 100 degrees (then it evaporates), whereas with salt (or anything else) dissolved in it, it can be brought to a higher temperature to cook food faster. Just as with the freezing point depression, the extent to which the boiling point is elevated depends on the concentration of what's dissolved (the higher the concentration, the higher the boiling point) and the nature of what's dissolved.


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## cobalt (8 Jan 2010)

..


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## Vanilla (8 Jan 2010)

Excellent post, Cobalt. Good clear explanation.


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## mystry4all (8 Jan 2010)

In the Netherlands, Even the Sea is frozen and we can walk on it


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## eddie7 (8 Jan 2010)

anyone on the titanic would have been able to answer that question....


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## AlbacoreA (9 Jan 2010)

http://en.wikipedia.org/wiki/North_Pole


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## sunrock (9 Jan 2010)

Pouring sea water on roads is a crazy idea. It would just turn to ice so we would have big sheets of ice on the road.The salt % would be diluted with contact with the ice/sludge on the road.If this was a solution it would be done in all the freezing coastal areas of the world.Put 4grams of salt in a liter of water and leave it outside and see if it freezes.


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## sustanon (9 Jan 2010)

Snow in Florida today. Ireland has mild winters due to the gulf stream, if the gulf is pumping snow and freezing conditions into Florida, then Ireland can kiss the temperate air supply from the gulf goodbye. Time tor Ireland to freeze according to it's latitude. Before you know it you'll have to buy snow tyres in the winter, stock salt for iced roads, equip every gritter with a plough, require citizens to keep their portion of the sidewalk clear, own a snowblower, and a snow shovel, drive large trucks and SUV's out of practicality, park the beemer and MX5 for the winter, wear snow shoes for fun, learn to ski, snowboard, and icefish...!

I live 10 degrees further south than Ireland in the US and we got 48 inches of snow in 3 days, just a fact of life, but we equip for it. Atlanta is going through the exact same problems as Ireland right now, they don't even own a single snow plough truck.


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## AlbacoreA (9 Jan 2010)

Its a little different in a Micra and a Ford 4x4 truck. 

Global warming. Who the heck named that anyway?


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## colin79ie (13 Jan 2010)

The bay where I live (in the west) froze over to the point it could be walked on. (I didn't!) Last time was 1982.


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