Boltzmann Suggested That A Diatomic Molecule Regarded As A Rigid Dumb Bell Or Figure Of Rotation, Might Have Only Five Effective Degrees Of Freedom, Since The Energy Of Rotation About The Axis Of Symmetry Could Not Be Altered By Collisions Between The Molecules.
For Diatomic Or Compound Gases Clerk Maxwell Supposed That The Molecule Would Also Possess Energy Of Rotation, And Endeavoured To Prove That In This Case The Energy Would Be Equally Divided Between The Six Degrees Of Freedom, Three Of Translation And Three Of Rotation, If The Molecule Were Regarded As A Rigid Body Incapable Of Vibration Energy.
Hence it may be inferred that this value is typical for diatomic molecules.
If two monatomic molecules, having energy of translation only, equivalent to 3 degrees of freedom, combined to form a diatomic molecule with 5 degrees of freedom, the energy lost would.
If two diatomic molecules, having each 5 degrees of freedom, combine to form a molecule with 6 degrees of freedom, we should have n = 2, or the energy lost would be 2pc per unit mass.
An early step accomplished by Ostwald in this direction is to define ozone in its relation to oxygen, considering the former as differing from the latter by an excess of energy, measurable as heat of transformation, instead of defining the difference as diatomic molecules in oxygen, and triatomic in ozone.
The Well Known Experiments Of Regnault And Wiedemann On The Specific Heat Of Gases At Constant Pressure Agree In Showing That The Molecular Specific Heat, Or The Thermal Capacity Of The Molecular Weight In Grammes, Is Approximately Independent Of The Temperature And Pressure In Case Of The More Stable Diatomic Gases, Such As 112,02, N2, Co, &C., And Has Nearly The Same Value For Each Gas.
For A Diatomic Gas, The Molecular Heat Would Be Nearly Five Calories, Or The Atomic Heat Of A Gas In The Diatomic State Would Be 2.5.
This Is The Value Of The Minimum Of Atomic Heat Calculated By Perry From Diatomic Hydrogen, But The Observations Themselves Might Be Equally Well Represented By Taking The Imaginary Limit 3, Since The Quantity Actually Observed Is The Mean Specific Heat Between O° And 182 5° C. Subsequent Experiments On Other Metals At Low Temperatures Did Not Indicate A Similar Diminution Of Specific Heat, So That It May Be Doubted Whether The Atomic Heats Really Approach The Ideal Value At The Absolute Zero.
In 1855, reviewing the various substances that had been obtained from glycerin, he reached the conclusion that glycerin is a body of alcoholic nature formed on the type of three molecules of water, as common alcohol is on that of one, and was thus led (1856) to the discovery of the glycols or diatomic alcohols, bodies similarly related to the double water type.
Alcohols are classified on two distinct principles, one depending upon the number of hydroxyl groups present, the other on the nature of the remaining groups attached to the carbon atom which carries the hydroxyl group. Monatomic or monohydric alcohols contain only one hydroxyl group; diatomic, two, known as glycols; triatomic, three, known as glycerols; and so on.
Changes of the first and second kind, according to our views of the constitution of molecules, are probably of very rare occurrence; in fact, chemical action appears almost always to involve the occurrence of both these kinds of change, for, as already pointed out, we must assume that the molecules of hydrogen, oxygen and several other elements are diatomic, or that they consist of two atoms. Indeed, it appears probable that with few exceptions the elements are all compounds of similar atoms united together by one or more units of affinity, according to their valencies.
Oxygen, nitrogen, hydrogen and carbon monoxide have the value 1.4; these gases have diatomic molecules, a fact capable of demonstration by other means.
But that it may be given by the ordinary diatomic molecule is exemplified by oxygen, which gives in thick layers by absorption one of the typical sets of bands which were used by Deslandres and others to investigate the laws of distribution of frequencies.