Re: [Phys-L] Temperature for the calorie?

["Anthony Lapinski" <alapinski@pds.org>]

I think the conversion (1 cal = 4.18 J) came from Joule's paddle wheel
experiment. A mass was allowed to drop, which was connected to a device
that mixed the water and increased its temperature.

I think the US is the only country with food labels that only list
Calories = 260. I have international food packages that say Energy = 130
kcal = 540 kJ...

Phys-L@Phys-L.org writes:
> On 01/27/2016 09:13 PM, I wrote:
>
> > Nobody in their right mind uses calories
>
> By that I meant small calories.  Obviously big Calories are still in
> use for food labels at present ... but even so, the FAO recommends
> gradually transitioning to joules.
>  http://www.fao.org/docrep/meeting/009/ae906e/ae906e17.htm
>
> That report makes sense to me.  It also says:
>
> > > Although not generally realized nutritionists actually have been 
> > > measuring energy in joules
>
> If/when it is necessary to convert:
>
> > > The Committee on Nomenclature of the International Union of 
> > > Nutritional Sciences concluded that most nutritionists use the 
> > > thermochemical calorie which equals 4.1840 J exactly.
>
> > > The thermochemical calorie actually approximates a "17° calorie"
> > > in contrast to the "15° calorie".
>
> which is as close as we are going to get to an answer to the 
> student's original question.
>
> ==================================
> Also I said:
>
> > I have no idea where the 4.184 J value comes from.  There is probably
> > some interesting history, but I don't know it.
>
> For some history, see
>  James L Hargrove
>  «Does the history of food energy units suggest a solution to "Calorie
> confusion"?»
>  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2238749/
> and references therein.
>
> > > The original published source defined the Calorie as the quantity 
> > > of heat needed to raise the temperature of 1 kg of water from 0 to
> > >  1°C.
>
> Hargrove makes a self-contradictory recommendation about the big
> Calorie.  He tries to equate (by definition) the 15 °C value with
> a joule-based value.  You can't have it both ways (unless you're
> going to redefine the joule, which would be absurd).  You can
> equate approximate values, but you can't equate definitions.  In
> any case, neither of these values agrees with what FAO recommends.
>
> I vote for the FAO approach.
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