Molecular Mass

142 NATURE VOL. 229 JANUARY 8 1971 CORRESPONDENCE Billion Confusion "the molar mass of protein X is 25,000 g In Vivo Difficulties mol-I", "the molecular mass of protein SIR,-The use of the terms "in vitro" and SIR,-Teodor Juskiewicz (Nature, 228, X is 25,000 daltons", and "the relative "in vivo" is now deeply entrenched in 297; 1970) referred to the American molecular mass (that is, molecular weight) the scientific literature. They are used practice of using the word "billion" to of protein X is 25,000".) to denote the difference between experi mean 109 instead of 10 12 and he appealed The 14th General Conference of ments performed outside the living to American colleagues not to use the Weights and Measures (CGPM) of the organism (although often with living misleading term parts per billion. International Bureau of Weights and tissue, and those carried out inside the I support Juskiewicz's appeal and Measures, convening in 1971, will con organism. The use of the two terms, suggest that it is time that some agree sider a recommendation approved in 1969 although hallowed by time, sometimes ment was reached to avoid misunder by the International Committee on causes difficulty, especially as editors of standings, which can arise by the use of Weights and Measures (CIPM) to include learned journals differ in the extent of this, at present, equivocal word. the mole as a base unit of the International their tolerance and degree of their To my mind the word "billion" means System of Units (SI), besides the six base pedanticism. Some editors are prepared a million to the power of two, similarly units on which the system was established to accept the terms virtually as the author "trillion" means a million to the power of in 1960 (the metre, the kilogram, the proposes, irrespective of syntactical or three and so on using suitable prefixes second, the ampere, the kelvin, and the scientific niceties. Some turn a blind eye added to the root "-illion" for numbers of candela). The additional base unit is to their suspiciously foreign sound and the type 106n (where n is an integer). needed to introduce SI units for the are prepared to admit them as current There is some need for a simple name "molar" physical quantities (molar English usage. Others, more severe, by for the number 109 which would be volume, molar mass, molar heat capa clapping the terms in itiilics, clearly still preferable to the rather clumsy "thousand cities, molar enthalpy of formation, etc.). regard them as aliens against whom the million". The word "milliard", obviously The appropriate physical quantity corre innocent reader must be warned. familiar to Juskiewicz and, I understand, sponding to the concept that different Hyphens between the two parts of each currently used in France, seems an substances have natural molecular consti term are not usually required, but on obvious choice. Furthermore, this word tutions (the word "molecular" here being occasions have been insisted upon by could form the basis of a system of used in a broad sense to include any the jlJiberal of outlook. Although naming large numbers of the type specified constituent entities, whether strictly "in vitro" and "in vivo" are 1O(6n+3) in the same way that "million" they be molecules, atoms, ions, ion pairs, adverbial phrases (and are only so used has for the 106n numbers. Thus 1015 or other aggregates) has not until recently by cognoscenti) they are now often would be called a billiard and 1021 a been identified by a commonly recognized misused as adjectives. Hence one reads trilliard, and so on. name. The name, "amount of sub of "in vitro experiments" and the even stance", has now been adopted by the more disgraceful "in vitro results". Even Yours faithfully, International Union of Pure and Applied "semi-in-vivo" (hyphenated surely) ex Chemistry, the International Union of periments have recently been threatened. R. M. BOROUGHS Pure and Applied Physics, and the Fowler, unfortunately, wrote before such International Organization for Standard indignities became common, and has 55 Wolsey Drive, ization to define a physical quantity nothing to say on the matter. Walton-on- Thames, proportional to the number of constituent With due awareness of Lord Chester Surrey entities of that substance (molecules or field's famous maxim, I should like to other entities, such as may be specified by suggest the introduction of two new a chemical formula). The proportional words to replace "in vitro" and "in vivo". ity factor is the same for all substances These would be the Simple adjectives Molecular Mass and may be taken to be the reciprocal of "vitral" and "vival" respectively. The the Avogadro constant. A unit for the SIR -Dr Edsall has explained (Nature, new words are short, their derivation is physical quantity, the mole, has long been 22S', 888; 1970) the useful distinctions etymologically pure and their meaning by recognized. The definition given by the past association) is clear, when referring that should be preserved among the CIPM in 1967, confirmed in 1969, and expressions, molecular mass, relative either to the tests themselves or to the included in the draft proposal prepared molecular mass (commonly called "mole results of tests. Moreover, they will for the 14th CGPM introducing fhe mole never need italics or hyphens. Reference cular weight") and molar mass. These as a base unit in the SI, is as follows I : to various technical dictionaries has dis quantities have respective dimensions: mass unity ("dimensionless") and mass The mol is the amount of substance of a closed, perhaps surprisingly, no prior use , I X (amount ofsubstance)- . Thecommon system which contains as .many eleI?entary of such adjectives. Although their intro entities as there are atoms m 0.012 kilogram duction, it is realized, would not be so unit of molar mass (not its dimension) is of carbon 12. traumatic as the introduction of SI units, the gram per mole (symbol, g/mol or nor so subversive as the substitution of g mol-I). Among recognized units of Note: When the mol is used, the elemen tary entities must be specified and may be "retinol" for vitamin A', there are bound molecular mass is the unified atomic mass atoms, molecules, ions, electrons, <?ther to be views in favour of the status quo unit (symbol u), defined as the fraction particles, or specified groups of such particles. and it would be interesting to hear them. 1/12 of the mass of an atom of the nUclid.e 12C (l u= 1.660 53 x 10 - 27 kg approxI If the 14th CGPM accepts the mole so Yours faithfully, mately), and for which Dr Edsall r~om defined as' an SI base unit, then the SI unit of molar mass will be the kilogram J. GREEN mends the simpler name, dalton, WIdely per mole (kg mol- '). This unit is large 19 Vineyard Hill Road, used by biochemists. (His examples of for ordinary chemical purposes and the Wimbledon, different statements expressing the same common unit, gram per mole (l g mo\-I London SW19 fundamental facts should have read: © 1971 Nature Publishing Group NATURE VOl. 229 JANUARY 8 1971 143 = 10-3 kg mol-I), will continue in use as Definition of Intelligence axiomatize the levels of the system inde an accepted decimal sub-multiple of the pendently and use negative feedback to SI unit. However, the SI unit itself is SIR,-Because others (Nature, 228, 1008; control the universality (requisite variety) suitable for expressing values of the molar 1970) have commented on the defini of both individual levels and the system as mass for macromolecular substances. tion of intelligence put forward by a whole. An essential part of the control Thus, one could add to Dr Edsall's Fatmi and Young (Nature, 228, 97; 1970) system is an order : disorder detector, as equivalent statements the alternative: and subsequently extended by myself suggested by H. B. Barlow in his letter. "the molar mass of protein X is 25 kg (Nature, 228, 589; 1970), I would like to This type of system would also imply that mol-I". make some further observations. the original definition of Fatmi and Although the unit of mass, "unified With regard to the letter from P. M. Young would be too broad to draw a atomic mass unit", is outside the SI, it Muller, the process of induction would be valid distinction between men and has been recognized by the CIPM as covered by my own definition, as would machines. useful in specialized fields of scientific "synthetic a priori". However, pro With regard to the letter from H. A. research I . Its value expressed in the SI cesses of reasoning from the part to the Cook. Any system is quantifiable if one unit, the kilogram, is derived by experi whole, from the particular to the general, knows what to measure and how to ment and is therefore not known exactly. and from the individual to the universal, measure it. It is another matter to Although in general one should be chary are not identical and isomorphic pro decide whether such a quantification of proliferating special names, the present cesses, nor are they symmetrical with provides an adequate description of the name for this unit, even when contracted respect to deduction and induction. system as a whole. The information to "atomic mass unit" (the term "unified" If we accept Godel's theorem, a single, theoretic brain model mentioned above distinguishing it from slightly different finite automaton with a phrase-structure implies a physiological symbol-processing earlier units based on 160 and on 0= 16), grammar can be either complete and con mechanism in the brain, which could form is not notably convenient or informative.

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