Council Committee on Nomenclature, Symbols and Terminology

A recurrent theme in reports from this Council Committee on Nomenclature, Terminology and Symbols (NTS) dating back at least a decade, regards the pending and unquestioned need to redefine the kilogram and the mole. NTS began its active participation in this issue with two goals:

1) to understand what is being done; and

2) to understand what it means to the practice of chemistry. 

The Conférence générale des poids et mesures (CGPM) is an inter-governmental conference of official delegates of member nations and the assigned supreme authority for all actions on weights and measures. At its 2011 meeting, the CGPM endorsed the concept of redefining all of the SI base units on physical constants deemed “invariants of nature,” a concept they had begun aggressively advocating for the kilogram since 2005. What immediately emerged as a corollary with NTS was a third goal 3) to influence establishment of valid, comprehensible, usable definitions, objectives that have been evaded by the international group. In regard to goal 3 a specification of the “Four Laws of Terminology” was introduced in NTS during the past year, modeled after the “Four Laws of Thermodynamics.” Particular significance is paralleled in the Zeroth Law of Thermodynamics, which defines the notion of temperature under certain conditions, and the Third Law of Thermodynamics which implies that one can only reach a temperature of zero Kelvin in an infinite number of steps. 

The Laws of Terminology

Zeroth Law of Terminology
Definitions exist, although not necessarily for everything

First Law of Terminology
Definitions must be exact and understandable

Second Law of Terminology
Definitions must be unambiguous and exception-free

Third Law of Terminology
The number of people understanding a definition approaches zero as the number of words used to satisfy the First and Second Laws of Terminology becomes infinite


(That Third Law is similar to the tongue-in-cheek definition of an “expert”: Experts are persons who know more and more about less and less until eventually they know everything about nothing.)

NTS has been tackling the intricate issue of the CGPM redefinitions owing to their opaqueness, inapplicability, and contradiction of the criteria for acceptable definitions of base quantities, criteria that justly recognize the need for easy understandability, realization everywhere, and invariance. (See Karol, P.J. Weighing the Kilogram. American Scientist, 2014, 102, 426-429; online at:, where it was demonstrated that

the proposed definition of the kilogram will actually involve a weight, rather than a mass, and as such is not “invariant”).

Note that the impact on quantitative chemistry will be negligible, but understanding what is being done, particularly from the point of education, has acutely retrogressed. More importantly, the sponsoring institutions which include the International Bureau of Weights and Measures and the National Institutes of Standards and Technology, whose proficiency is in making measurements and evaluating standards, do not have either the expertise or uncompromised judgments on definitions. That should be in the hands of scientists, not metrologists.

The proposed redefinition of the kilogram, a breach of the CGPM’s own requirements and also now of the First and Third Laws of Terminology, would read as follows:

“The kilogram, kg, is the SI unit of mass; its magnitude is set by fixing the numerical value of the Planck constant to be equal to exactly 6.626 069 … X 10-34 when it is expressed in the unit s-1 m2 kg, which is equal to J s.”

The redefinition will force the classical, easily understood concept of mass into the quantum realm, the only physical quantity so encumbered. Minimal progress towards realizing (mise en pratique) the redefinition in relation to the Planck constant has been noted by the CGPM. Data do not yet appear to be sufficiently robust to move forward, a euphemism for unresolved lack of agreement among metrology labs using multimillion dollar watt balances that depend on the Earth’s gravitational constant, definitely not an invariant of nature. Continued effort on improving the data has been encouraged such that a resolution that would replace the current definition with the above revised CGPM definition could be adopted at the 26th meeting. 

At the August 2014 ACS National Meeting in San Francisco, the symposium “Redefining the Mole and Kilogram – Impact on Chemistry” was sponsored by NTS, and co-sponsored by the Division of Analytical Chemistry and the International Activities Committee. Among the presentations was one by this author, “The new SI kilogram:  misère en pratique” enumerating the fallacies of the CGPM definition.  

An even shoddier example of poor definition is “amount of substance,” the SI base quantity representing the mole:

“Amount of substance is a quantity proportional to the number of specified elementary entities N in a sample.  The proportionality constant is the same for all substances, and is the reciprocal of the Avogadro constant NA, so that amount of substance is defined by the equation n = N/NA. The entities may be atoms, molecules, ions, electrons, other particles or specified groups of particles.”

At the San Francisco symposium, NTS member Carmen Giunta presented data in his talk “Defining the mole and kilogram for chemistry education” documenting that chemists by and large simply do not use the so-called physical quantity term “amount of substance” for the mole. And likely never will.

The NTS is involved in a “David and Goliath” battle and encourages active participation by the troops.

Paul Karol, Former Chair, Council Committee on Nomenclature, Terminology and Symbols