hold on...

say 0.5 US gal of 100 proof vodka (50% alc), and say tank has 45
litres of water, final conc. of alcohol will be:

1.8 % (v/v) alcohol. which will depress freezing point by not much
(not going to do the delta T calc.)

say its 180 proof vodka, 90% etoh, then final conc when added to 45
litres of water will be :

3.2% (v/v)

you need 10% (v/v) to get a -4 C freezing point depression.

Half a gallon of vodka, at any available strength will not work

alistair

On 13-Mar-11, at 12:47 PM, Jim Arnott wrote:

> A half gallon of vodka comes to mind....
>
> Jim
>
>
> On Mar 13, 2011, at 8:56 AM, Mark L. Hineline wrote:
>
>> Next weekend I'm going to be on the Colorado Plateau for three
>> nights.
>> Daytime temps in the 50s, nighttime down into the 20s.
>>
>> Are there any tricks to keeping the water tank happy and unfrozen?
>>
>> Mark