VOL. 79, No. 2039 acid. The sodium salt of glycyl-glycine behaves in a manner intermediate between the sodium salt of gly- cine and of £ amino caproic acid. Despite its large dipole moment, the apparent molal volume of isoelec- tric £ amino caproic acid, with its long hydrocarbon chain, changes very little indeed in solutions contain- ing less than 25 per bent. of amino-acid. This type of behavior is also characteristic of most proteins, whose great apparent density in solution diminishes but little even in the concentrations which obtain in biological systems. EDWIN J. COHN HARVARD MEDICAL SCHOOL "EXERGIC" AND "ENDERGIC" REACTIONS' IN the consideration of chemical reactions it is often necessary to distinguish between (a) those processes which occur spontaneously, for example, in a primary cell, that is, which are capable of doing work; and (b) those which require work to be done in order to bring them about, for example, the electrolytic decom- position of water into hydrogen and oxygen. Ther- modynamically, these types of reaction are distin- guished as resulting in (a) a decrease in free energy and (b) an increase in free energy. It is proposed to designate these two types of reac- tion respectively as (a) "exergic," that is, capable of giving out work; and (b) "endergic," that is, taking in work. They are derived from the Greek root "ergon," work. At first it might appear that the need for such terms is met by the customary expressions "exother- mie" and "endothermic." It has long been known, however, that these terms are inadequate to describe chemical reactions, and hence the concept of free energies was introduced. As above noted, the new terms apply to the free energy and not to the total energy of the process. The majority of reactions that are exothermic are also exergic, and most of those that are endothermic are endergic, but the relation is not universal. Thus, Lewis and Randall2 cite a cell in which the reaction Ag(s) +HgCl(s) =AgOl(s) +Hg(l) yields at 2980 K a potential of 0.0455 V (that is, according to the above definition the process is exergic), although the chemical reaction is endo- thermic, with a total heat change, A H298, equal to +1280 cal. In order for the cell reaction to occur Jaken from the surround- rector of the U. S. Graw Hill Book Co., Similarly, it follows that the reverse reaction Hg (l) + AgCl (s) = Ag (s) ± HgCl (s) is exothermic, that is, A H1298 =- 1280 cal.; but ill order for this process to occur in a cell, work equiva- lent to 0.0455 V must be done upon it, that is, the process is endergic. The need for such terms was evidently felt by 11l J. Creighton,3 who states that chemical changes ane called 'exo-electrical' when they develop electrical energy and 'endo-electrical' when they absorb electri- cal energy." His terms have much the samiie meanina 0 as those now proposed, but are somewhat less generao, in their application. No new concepts are involved in the prolpose(l terms. Justification for their use must be found ii their conciseness or pedagogic convenience. Tlle pro- posed definitions are as follows: "Exergic reactions are those which occur Aviti decrease in free energy." "Endergic reactions are those which occur -with ai increase in free energy." \Vr. Bi.l.Ai U. S. BUREAU OF STANDARDS 3 ''Principles and Applications of Electrochemistry, Vol. 1, 2nd ed., p. 8. John Wiley and Sons, New Yvork, 1928. BOOKS RECEIVED BAKER, H. P. Principles of Geometry. Vol. V, Analy- tical Principles of the Theory of Curves. Pp. x+247. $4.50. Vol. VI, Introduction to the Theory of Alg- braic Surfaces and Higher Loci. Pp. ix+308. $4.75, Cambridge University Press, Macmillan. Bulletin of the National Research Council No. 90: P7hy.>- ics of the Earth, Vol. VI, Seismology. Pp. 223. Ni tional Research Council. $2.00. COLLINS, A. FREDERICK. The Amateur Machinist. Pp xiv + 300. 157 figures. Appleton-Century. $2.00. GADOW, H. F. The Evolution of the Vertebral Columo)i. Edited by J. F. Gaskell and H. L. H. H. Green. Pp xiv + 356. 123 figures. Cambridge University Press, Macmillan. $6.75. GLASSER, OTTO. Wilhelm Conrad Rontgen and the EarlIy History of the Roentgen Rays. Pp. x + 494. 96 figure". Charles C. Thomas. $6.00. HENRICI, ARTHuR T. The Biology of Bacteria. Pp. x 472. 112 figures. Heath. $3.60. KOLLER, L. R. The Physics of Electron Tubes. Pp. xiii +205. 67 figures. McGraw-Hill. $3.00. MALLOCH, J. R. Diptera of Patagonia and South Chilo. Part VI: Fascicle 4, Acalyptrata, Pp. 177-391. Illus- trated. Fascicle 3, Ephydridae (Supplement), Syr- phidae, Conopidae. Pp. 117-175. Illustrated. Britisli Museum. PALM, FRANKIAN C. Europe Since Napoleon. Pp. ix- 890. Illustrated. Ginn. $4.00. REID, MARY E. and MARJORIE E. J. CHANDLER. [Fht- London Clay Flora. Pp. viii + 561. 33 plates. 17, figures. British Museum. E 2, 10 s. SEWALL, HENRY. Society and the Natural Law. Pp. 7-9. Badger. $2.00. WEST, CLARENCE J. and CALLIE HULL. Bulletin of 1lb1 National Research Council, No. 91: Industrial Researchl Laboratories of the United States. Fifth editioni. Pp. 223. National Research Council. $2.00. SCIENCE 84
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VOL. 79, No.2039
acid. The sodium salt of glycyl-glycine behaves in amanner intermediate between the sodium salt of gly-cine and of £ amino caproic acid. Despite its largedipole moment, the apparent molal volume of isoelec-tric £ amino caproic acid, with its long hydrocarbonchain, changes very little indeed in solutions contain-ing less than 25 per bent. of amino-acid. This typeof behavior is also characteristic of most proteins,whose great apparent density in solution diminishesbut little even in the concentrations which obtain inbiological systems.
EDWIN J. COHNHARVARD MEDICAL SCHOOL
"EXERGIC" AND "ENDERGIC" REACTIONS'IN the consideration of chemical reactions it is often
necessary to distinguish between (a) those processeswhich occur spontaneously, for example, in a primarycell, that is, which are capable of doing work; and(b) those which require work to be done in order tobring them about, for example, the electrolytic decom-position of water into hydrogen and oxygen. Ther-modynamically, these types of reaction are distin-guished as resulting in (a) a decrease in free energyand (b) an increase in free energy.
It is proposed to designate these two types of reac-tion respectively as (a) "exergic," that is, capable ofgiving out work; and (b) "endergic," that is, takingin work. They are derived from the Greek root"ergon," work.At first it might appear that the need for such
terms is met by the customary expressions "exother-mie" and "endothermic." It has long been known,however, that these terms are inadequate to describechemical reactions, and hence the concept of freeenergies was introduced. As above noted, the newterms apply to the free energy and not to the totalenergy of the process. The majority of reactions thatare exothermic are also exergic, and most of thosethat are endothermic are endergic, but the relationis not universal.
Thus, Lewis and Randall2 cite a cell in which thereaction
Ag(s) +HgCl(s) =AgOl(s) +Hg(l)
yields at 2980 K a potential of 0.0455 V (that is,according to the above definition the process isexergic), although the chemical reaction is endo-thermic, with a total heat change, A H298, equal to+1280 cal. In order for the cell reaction to occur
Jaken from the surround-
rector of the U. S.
Graw Hill Book Co.,
Similarly, it follows that the reverse reaction
Hg (l) + AgCl (s) = Ag (s) ± HgCl (s)
is exothermic, that is, A H1298=- 1280 cal.; but illorder for this process to occur in a cell, work equiva-lent to 0.0455 V must be done upon it, that is, theprocess is endergic.The need for such terms was evidently felt by 11l
J. Creighton,3 who states that chemical changes anecalled 'exo-electrical' when they develop electricalenergy and 'endo-electrical' when they absorb electri-cal energy." His terms have much the samiie meanina0as those now proposed, but are somewhat less generao,in their application.No new concepts are involved in the prolpose(l
terms. Justification for their use must be found iitheir conciseness or pedagogic convenience. Tlle pro-posed definitions are as follows:
"Exergic reactions are those which occur Avitidecrease in free energy."
"Endergic reactions are those which occur -with aiincrease in free energy."
\Vr. Bi.l.AiU. S. BUREAU OF STANDARDS3 ''Principles and Applications of Electrochemistry,
Vol. 1, 2nd ed., p. 8. John Wiley and Sons, New Yvork,1928.
BOOKS RECEIVEDBAKER, H. P. Principles of Geometry. Vol. V, Analy-
tical Principles of the Theory of Curves. Pp. x+247.$4.50. Vol. VI, Introduction to the Theory of Alg-braic Surfaces and Higher Loci. Pp. ix+308. $4.75,Cambridge University Press, Macmillan.
Bulletin of the National Research Council No. 90: P7hy.>-ics of the Earth, Vol. VI, Seismology. Pp. 223. Nitional Research Council. $2.00.
COLLINS, A. FREDERICK. The Amateur Machinist. Ppxiv + 300. 157 figures. Appleton-Century. $2.00.
GADOW, H. F. The Evolution of the Vertebral Columo)i.Edited by J. F. Gaskell and H. L. H. H. Green. Ppxiv + 356. 123 figures. Cambridge University Press,Macmillan. $6.75.
GLASSER, OTTO. Wilhelm Conrad Rontgen and the EarlIyHistory of the Roentgen Rays. Pp. x + 494. 96 figure".Charles C. Thomas. $6.00.
HENRICI, ARTHuR T. The Biology of Bacteria. Pp. x472. 112 figures. Heath. $3.60.
KOLLER, L. R. The Physics of Electron Tubes. Pp. xiii+205. 67 figures. McGraw-Hill. $3.00.
MALLOCH, J. R. Diptera of Patagonia and South Chilo.Part VI: Fascicle 4, Acalyptrata, Pp. 177-391. Illus-trated. Fascicle 3, Ephydridae (Supplement), Syr-phidae, Conopidae. Pp. 117-175. Illustrated. BritisliMuseum.
PALM, FRANKIAN C. Europe Since Napoleon. Pp. ix-890. Illustrated. Ginn. $4.00.
REID, MARY E. and MARJORIE E. J. CHANDLER. [Fht-London Clay Flora. Pp. viii + 561. 33 plates. 17,figures. British Museum. E 2, 10 s.
SEWALL, HENRY. Society and the Natural Law. Pp. 7-9.Badger. $2.00.
WEST, CLARENCE J. and CALLIE HULL. Bulletin of 1lb1National Research Council, No. 91: Industrial ResearchlLaboratories of the United States. Fifth editioni. Pp.223. National Research Council. $2.00.
SCIENCE84
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