Measure is equivalent to 4.177 joules per calorie at 16.5° C., on the scale of Joule's mercury thermometer.
10° 15° 20° 2 5° 3 O ° 35° Joules Per Cal.
Expressed In J Oules Per Calorie The Result Is 4.1832, Which Agrees Very Closely With The Value Foand By Rowland As The Mean Over The Range 15° To 20° C. The Value 4.183 Is Independently Confirmed In A Remarkable Manner By The Results Of The Electrical Method Described Below, Which Give 4.185 Joules For The Mean Calorie, If Rowland'S Value Is Assumed As The Starting Point, And Taken To Be 4.180 Joules At 20° C.
By Ohm'S Law, And By The Definition Of Difference Of Electric Pressure Or Potential, We Obtain The Following Alternative Expressions For The Quantity Of Heat H In Joules Generated In A Time T Seconds By A Current Of C Amperes Flowing In A Wire Of Resistance R Ohms, The Difference Of Potential Between The Ends Of The Wire Being E = Cr Volts: H=Ect=Crt=E Z T/R.
Griffiths' Final Result For The Average Value Of The Calorie Over This Range Was 4.192 Joules, Taking The E.M.F.
The Result Found Was 4.191 Joules Per Calorie At 19° C. This Agrees Very Well With Griffiths Considering The Difficulty Of Measuring So Small A Rise Of Temperature At 2° With A Mercury Thermometer.
A Steady Current Of Liquid, Q Grammes Per Second, Of Specific Heat, Js Joules Per Degree, Flowing Through A Fine Tube, A B, Fig.
The Result Calculated On These Assumptions Is Given In The Last Column In Joules, And Also In Calories Of 20° C. The Heatloss In This Example Is Large, Nearly 4.5% Of The Total Supply, Owing To The Small Flow And The Large Rise Of Temperature, But This Correction Was Greatly Reduced In Subsequent Observations On The Specific Heat Of Water By The Same Method.
Assoc. Report, 1899, with a slight modification Specific Heat Of Water In Terms Of Unit At 20° C. 4.180 Joules to allow for the increase in the specific heat below 20° C. This was estimated in 1899 as being equivalent to the addition of the constant quantity 0.020 to the values of the total heat h of the liquid as reckoned by the parabolic formula (5).
This unit is taken as being 4.180 joules per gramme-degree-centigrade on the scale of the platinum thermometer, corrected to the absolute scale as explained in the article Thermometry, Which Has Been Shown To Be Practically Equivalent To The Hydrogen Scale.
The Value 4.180 Joules At 20° C. Is The Mean Between Rowland'S Corrected Result 4.181 And The Value 4.179, Deduced From The Experiments Of Reynolds And Moorby On The Assumption That The Ratio Of The Mean Specific Heat O° To 100° To That At 20° Is 1.043'6, As Given By The Formulae Representing The Results Of Callendar And Barnes.
It Was Proposed By A Committee Of The British Association To Select The Temperature At Which The Specific Heat Was 4.20O Joules, Leaving The Exact Temperature To Be Subsequently Determined.
The energy stored up in the jar in joules is expressed by the value of CV 2, where C is the capacity measured in farads and V the potential difference of the coatings in volts.
If the capacity C is reckoned in microfarads then the energy storage is equal to CV 2 /2 X 19 6 joules or 0.737 CV 2 / 2 X 10 6 foot-pounds.
The unit of heat assumed in the table is the calorie at 20° C., which is taken as equal to 4.180 joules, as explained in the article Calorimetry.
Thisconstant, now designated as Joules equivalent, is the principal experimental datum of the science of thermodynamics.
Moorby, gives 778 as the mean value of Joules equivalent through the range of 32 to 212 F.