ALCOHOL

n. A?lko-ho?l. Deriv., Ar., al-kochl, a callyzium, from kachala (Hebr., käkhal), to stain or paint. Lat., alcohol (m. or n.; gen., alcoho'lis). Fr., alcool. Ger., Alkohol. It., alcool, alcol, Sp., alcohol, Also written alcaol and alkohol. 1. Antimon: or its trisulphide (used in the East as a pigment for the eyebrows). 2. A fine powder used as an application to the eyes. [San ays GIS) 3. A OR, finely divided powder. “ A. est pulvis subtil is sim us,* [B, 50.] 4 Hence, from the sense of tenuity thus acquired, the e ence or inner principle of anything. 5. In its common acceptation, the e ence or spirit of wine, a. vin i. Common or ethyl a. [See ETHYL a.] 6. In chemistry, a generic term (first used in this sense by Dumas and Péligot in 1834 or 1835) for a series of comounds of which ethyl a. is a type, and which may be regarded as Rerived from the hydrocarbons by the replacement of one or more atoms of hydrogen in the latter by one or more molecules of hydroxyl; or they may be considered as formed by the substitution of a univalent, bivalent, or trivalent hydrocarbon for half the hydrogen in one, two, or three molecules of water (H,0). The a’s.ccordingly, the general formula (CaHm)’OH, (CpHq)’(OH)o, (C:Hr)”/(OH)s, ete., being designated as monatomic, diatomic, tri. atomic, etc., according to the number of hydroxyl moleeules which they contain, and receiving their specific names from that of the radicle (CaHm, etc.) combined with the hydroxyl (e. g., C,H,.0H, ethyl a., CsH,.(OH)s. glyceryl a. X analogues of the inorganic hydrat ota a, and, like the latter, they red basic properties. On oxidation they are converted into aldehydes, ketones, and organic acids. [B, 2,3, 4, 39, 50.) See also GLYCOL. GUYCERIN, CARBINOL, and PHENOL, and for the individual a’s see the major list—Absolute a. Lat., a. absolutum on absolutus). Fr., alcool absolu, Gr., wa erfreier (oder absoluter) Alkohol. It., alcool a oluto. Sp., a. absoluto. Syn.: anhydrous a. Ethyl a. deprived of water. See ETHYL a.—Albuminous a. A solution of white of egg in ordinary (ethyl) a. [B, 97.] — A. absolutum, A. absolutus. Absolute a. See ETHYL a.—A. aceti. Fr., alcool de vinaigre. Ger., E igalkohol. Acetic acid. [B, 48.]—A. æthere us ferratus. See Tinctura FERRI CHLORATI e@there a.—A. alcalisatum, A. alkalis a tum. 1. Nearly absolute ethyl a. obtained by the dehydrating action of pota ium carbonate upad ordinary a. [B, 97.) ETHYL A. 2. An alcoholic solution of potash. 1B. 119.]—A. ammoniac ale a rom at i cum, A. ammoniac a tum a rom at is a tum. See Spii 8 AMMONIÆ aromatic us.—A. ammon iæ auisatum. See tus AMMONIA an is at us—A. ammoniz et guaiac i. See Tinctura GUAIACI ammon i at a.—A. ammonia tum, A. ammonia tum a rom at i cum, A. ammonia tum fœtidum. See Spiritus ammonim, Spiritus AMMONIÆ aromatic us, and Spiritus AMMONIÆ fœtid us.—À. amylicum [Br. Ph.]. See AMyL a.—A. a rom at i cum. See SPIRITUS aromatic us.—A. a rom at i cum ammonia tum. See Spiritus AM- MONIÆ aromatic us,—A. a rom at i cum sulphur i cum. ACIDUM SULPRURICUM a rom at i cum.—A. aromatic us ammon i at us. See Spiritus AMMONLE aromatic us.—A. camphor a tum. See Spiritus CAMPHORE.—A. camphor a tum crocatum. See Agua pestilential is—A. camphor at us, A. camphor at us debilior. The equivalents for the teinture de camphre concentré and teinture de camphre faible of the Fr. Codex. [B.] See Spiritus CAMPHORÆ.— A. castor i a tum. Tinctura CASTOREL—A. concentrati imum. Very strong ethyl a. See ETHYL a.—A. cum aloe, A. cum aloe perfoliata. See Tinctura ALOES—A. cum a rom at i bus compos it us. A eye rere nl corresponding to the tinctura cinnamomi compos it a of the old Lond, Ph. [B, 97.] See TINcTURA. aromatic a.—A. cum a rom at i bus sulphuric at us. See ACIDUM SUL- PHURICUM a rom at i cum.—A. cum citro aurantio. See Tinctura AURANTII.—A. cum crotone cascarilla. RILLÆ—A. cum ferri sulphate tart a riz at us. See Tinctura MARTIS aperitiva.—A. cum guaiaco officinal i ammon i at us. See Tinctura avatact ammoniuta.— A. cum opio. See Tinctura opi1.—A. cum rheo. See Tinctura RHEL—A. cum succi no. See Tinctura sUCcINL—A. cum suiphate ferri tartar is at us. See Tinctura MARTIS aperitiva.—A. cum tartrate pota æ ferratus. See Tinctura FERRI tartar is at a.—A. dehydrogenatum, A. dehydrogeuatus. Aldehyde.—A. dilutum, A. dilutus. Dilute a. “See under ETHYL a.—A. ethylicum (Br. Ph.]. Absolute a. ETHYL a.—A. ferrat See Tinctura FERRI cHLorID I.—A. ferratum æthereum. See Tinctura FERRI CHLORATI etherea.—A. ferratus. See Tinctura FERRI CHLORID I.—A. formic arum distill a tum. See Spiritus FORMIC ARUM. » fortius. Stronger a.; a title official in several pharma copæias, See ETHYL 4.—A. helenii compos i tum. See SpIRITUS carminativus—A. fodii. See Tinctura tov1.—A. juniper i compos i tum. See Spiritus JUNIPER I compos it us.—A. lamp. See under Lamp.—A. mart is. See Alcoholized mon (Ist def.).—A. methyl i cum. Methyl a.—A. nitrico-ætherenm. Nitrous ether; ethyl nitrite. {B, 97.]—A. nitricum. See Spiritus ÆTHERIS NITROSI.—A. nitricum be regarded as ( See Tinctura casca- | æthereum. See A. nifrico-wthereum.—A. ot crystallization. Fr., alcool de cris tallis at i on. Ger., Krystallisationsalkohol. It., aicool di cristallizzazione. Sp., a. de cristalizacién. A. which unites molecule by molecule with a crystalline substance, and, like water of crystallization, helps to maintain the crystalline form of the latter. Thus sodium ethylate, when crystallized from an alcoholic solution, contains 2 molecules of a, of crystallization, C,H,O.Na +2C,H,0, and in this form consists of colorle acicular crystals, but when deprived of its a. of crystallization becomes a white amorphous: powder, Both methyl a. and ethyl a. unite in this way with salts. fey ë of sulphur. See under SuLPHUR.—A. of the fatty series. See Fatty a.—A. opii dilutum. See Tinctura opi simplex.—A. ota æ. An alcoholic solution of potash. [B, 87.]—A. radicle. under RanicLe.—A. rectificati imum, A. rectificatum. Rectified a. By See ETHYL a.—A. salviæ vulnerarius. See under SALVIA.—À. saponatum. See Tinctura saponis.—A. serpylli compos i tum. See À. SERPYLLI compos i tum.—A. sulfurico-æthereum. See À. sulphurico-wthereum.—A. sulfur is. Sce A. of SULPHUR—A. sulphuric a tum. See MrxTURA sulfuric a acid a.—A. sulphurico-æthereum. Impure ether mixed with ethyl a. {B, 97.]—A. sulphurico-æthe rens ferri, A. sulphurico-æthere us mart i at us. See Tinctura FERRI CHLORATI Œthere a. —A. sulphur i cum. See Mrxtura sulfuric a acid a.—A. sulphur i cum æthereum. See À. sulphurico-ethereum.—A. suiphuricus cum ferro. See Tinctura FERRI CHLORATI cet here a.—A. suiphuris. See A. of suLpuuR.—A. terebinth inæ. il of turpentine. [B,97.]—A. thermometer. See under THERMOMETER.—A. vin i. 1. The name (meaning spirit of wine) by which ethyl a, was known before the term a. was sonlied to that substance exclusively. (Para cels us (B, 50).] See A. 2. In the old editions of the Sp. Ph., urified spirit obtained by the re-distillation of a, vin i commune, fs 97.]—A. vin i alcoholizatum. Stron; ethyi a. (B,97.]—A. vin i commune. Rectified spirit. [B, 97.]—-Aldehyde a. Fr., alcool-aldéhyde. Ger., Aldehydalkohol. A substance which has at once the structure and properties of an a. and an aldehyde. Aldol, CH,.CH(OH).CH,.C(H):O, is an example, containing the molecuie C(Ïl):O characteristic of the aldehydes, and being converted into a monobasic acid on oxidation, while it also contains a molecule of alcoholic ny apoxyl (OH). The aldehyde a’s may be regarded as glycols whose conversion into aldehydes has been incompee they being intermediate in structure between ordinary aldedes and double aldehydes. [B.]—Ammioniated a. See Spiritus AMMONLE.—Amylic a. See AMYL 4.—Anhydrous a. Fr., alcool anhydre. Ger., wa erfreier Alkohol. It., alcool anidro. See Absolute a.—Aqueous a. See Hydrated a—Aromatie a. Fr., alcool a rom at i que. Ger., a rom at is cher Alkohol, It., alcool aromatico. Sp., alcohol aromdtico. An a. the radicle of which contains phenyl or one of its homologues. The aromatic a’s proper are derived from the series of hydrocarbons homologous with benzene by the substitution of hydroxyl for an atom of hydrogen not in direct connection with a carbon atom of the benzene nucleus. Their constitution is, therefore, expre ed by the general formula, CeHe-ChHzn(OH), in which the hydrogen of the benzene-residue, CgH,, admits of further replacement by various radicles. The aromatic a’s may also be regarded as derived from the series of monatomic alcohols of the fatty series by the substitution of phenyl or any univalent radicle of the aromatic series for hydrogen. Thus, benzyl a., CeH;-CH,(OH), ay be regarded as methyl a. in which phenyl replaces hydrogen. ‘The aromatic a's are isomeric with the monatomic phenols, which are, indeed, frequently cla ed under the same head. {B, 4.] See also Aromatic aLYcoL and PHENOL — Caustic a. Fr., alcool caustique. It., alcool caustico. Sp. catistico. Sodium ethylate. [B.|—Common a. Lat., a. vin i, spiritus rectificatus. Fr., alcool ordinaire (ou vinique). Ger., gewohnlicher Alkohol. Rectified spirit; the ordinary ethy] a. of the shops. See ETHYL a.—Condensed a. A term sometimes applied to saccharine and amylaceous substances, regarded as derivatives of the a’s. [L, 63.._—Dehydrogenated a. Lat:,a. dehydrogenatum (seu dehydrogenatus). Fr., alcool déshydrogéné. Aldehyde. [B.]—Deodorized a. yl a. from which odorous and coloring matters have been removed by filtration through charcoal. [B, 14.|—Diacid a. Fr.,alcool bi-acide. Ger., zweiwerthiger Alkohol. See DrA- TOMIC A.—Diatomic a, Fr., alcool biatomique. Ger., zweiatomiger Alkohol. It., alco old i a to mico(o biatomico). Sp.,a. diatémico. ‘An a. formed by the substitution of a bivalent organic radicle for half the hydrogen in 2 molecules of water, or by replacing 2 atoms of hydrogen in a hydrocarbon by 2 molecules of hydroxyl. There are 8 sets of diatomic a’s: 1. The glycols, derived from hydrocarbons of the fatty series. 2. The aromatic glycols, derived from the glycols by the substitution of phenyl or its homologues for hydrogen. 3. The diatomic phenols, derived directly from hydrocarbons of the aromatic series. The last are often considered as forming a up distinct from the a’s proper. The diatomic a’s are also called ihydric a’s, diacid a’s, and dibasic a’s. because they contain 2 molecules of hydroxyl replaceable by acid radicles, forming two sets of derived salts or compound ethers, and on oxidation giving rise to both monobasic and dibasic acids. [B, 2, 4, 6.}—Dibasic a, Fr., alcool bibasique. Ger., zweibasischer Alkohol. ” It., alcool dibasico (0 bibasico). Sp.,a. dibäsico. See Diatomic a—Diglucosie a. Fr, aia diglucosique. us penoric (tent a cla eeanese tomic a’s including sugar and gum. S olyglucosic a.—Dihydrie a. Fr., alcool bihydrique. Ger., dihydrischer Alkohol. It., alcool biidrico. See Diatomic a.—Dilute a. Lat., a, dilutum, spiritus dilutus(seu tenuior). Fr., alcool ditué. Ger., verdiinnter lkohol (oder Spiritus). It., alcool diluto. Sp., @. débil. Ethyl a. containing more or le water. See ETHYL a.—Diprimary a. 5 alcool di-primaire. Ger., diprimärer Alkohol. A diatomic a. in which the two alcoholic hydroxyl molecules are united to the two terminal carbon atoms of the hydrocarbon chain, e. g., — Hy—CH,—CH,(OH). [B,4.]— Disecondary a. Fr. aicool di-second a ire. Ger., disekun ärer Alkohol. A diatomic a. in which both the alcoholic hydroxyl molecules are united to carbon atoms which are themselves combined each with 2 other carbon atoms, e. g., O, no; 07, not; O$, whole; Th, thin; Th?, the; U, like oo in too; U*, blue; U%, iull; U4, full; U*, urn; U®, like ü (German). 20 —CH,(OH)—CH, OH)—CH. B, 4.|—Ditertiary a. Fr., al- | and isopropyl methyl carbinol) and to secondary hexyl a. (iso- Ce e “Gekcdttentidter alkohol À diatomde & in which | butylmethyWearbinol). [B.J-Pyroligneous a. Fr., esprit’ pyro- D e eT een S ofher carbon, atoms, | [K.] Hoct Hoa ee Lat epiritus rectiftealia, a. rectipcatum. Ern i 3 n atom: J e %, n A VD C © | Kicnalinectité. Gerrectificérter* AlkoNoli(oder Getel Maar tcac? e 9 GH YOCOM—COMK GH. [B,4.]—Druggist’s a, Ordinary a. prepared by distillation as it is kept in the sho) [B, 14.|—Fatty ar An a. aeived from a hydrocarbon of the fatty series, BI Hex a basic a., Hexacid a., Hexatomie a., Hexhydric a. Er., alcool hexabasique (ou hexatomique, ou hexhydrique). Ger., sechs basis cher (oder sechs atom i ger, oder hexahydrischer) Alkohol. It., alcool e abasico (0 e a to mico, 0 e aidrico), An a. formed by relacing half the hydrogen in 6 molecules of water by a sexvalent Bydrocarbon, or by sul eta o) molecules of hydroxy] for 6 hydrogen atoms in a hydrocarbon. The hex atomic a’s comprise nearly all of the saccharine proximate principles, such as cane and milk-sugar; and their anhydrides constitute starch, cellulose, glycogen, etc. ' [B, 2.]—Hydrated a. Fr., alcool hydraté. Ger.,wa eriger Alkohol. It., alcool idrato. Sp. a. hidratado. Syn.: ueous a. Ethyla. still containing water from which mere distillation will not free it. [B.]—Iso-a. Fr., iso-alcool. Ger., Isoalkohol. It., iso-alcoot. An a. derived from a hydrocarbon which does not present the normal form, 7. e., contains carbon atoms which are directly united with more than 2 other carbon atoms, e. g., isobutyl a., CH,—C(CH,)H—CH,(OH), where the second carbon atom is directly united with 3 other carbon atoms., 4.)—Monacid a., Monad a. Fr., alcoul monacide. Ger., einwerthiger Alkohol. See Monatomic a. —Monatomic a. Fr., alcool mono atom i que. Ger. einatomiger Alkohol. It., alcool mono a to mico. Sp., a. mono atémico. Ana. formed by the substitution of a univalent hydrocarbon for half the hydroen in 1 molecule of water, or by replacing 1 atom of hydrogen in a fiydrocarbon by a molecule of hydroxyl. e monatomic a’s comrise 8 varieties: 1. Monatomic a’s of the fatty series derived from ydrocarbons of the fatty series. 2. Aromatic a’s (q. v.). 3. Monatomic phenols derived directly from the aromatic hydrocarbons. ‘The last are by many. reearded as distinct from the a’s proper. The monatomic a's are called also monacid, monobasic, and monohydric a's, because they contain but 1 molecule of hydroxy] replaceable by acid radicles, and hence form but one set of saline derivatives(compound ethers), and by their oxidation give rise to but one set of acids which are monobasic. [B, 2, 4,6.] See PHENoL.—_Monobasic a., Monohydric a. Fr., alcool mon obas i que (ou monohydrique). Ger., einbasischer (oder monohydrischer) Alkohol. It., alcool monobasico (0 monoidrico). Sp., a. monobasico (6 mono hid rico). See Monatomic a—Normal a. Fr., alcool normal. Ger., normaler Alkohol. It., alcool normale, Sp.,a.normal. Ana, in which the hydrocarbon from which it is derived presents the normal form,. e., consists of a chain of carbon radicles no one of which is directly connected with more than 2 other carbon radicles. [B, 4.]—Pent a basic a., Pent a hydric a. Fr., alcool pen tab as i que (ou pentahydrique). Ger., fünfbasischer (oder pentahydrischer) Alkohol. It., alcool pentabasico (0 pent aid rico). Sp., a. pentabdsico (6 pent a hid rico). See Pentatomic a.—Pentatomic a. Fr., alcool pent atom i que. Ger.. fiinfatomiger Alkohol. It., alcool pent a to mico. Sp.,a. pent atômico. Ana. formed from 5 molecules of water by the substitution of a quinquivalent radicle for half the hydron; or derived from a hydrocarbon by replacing 5 hydrogen atoms y 5 molecules of hydroxyl. Instances of such a's are pinite and GUcECHES [B, 2.._—Pentylic a. See AmyL A.—Polyatomic a., olybasic a., Polyhydric a. Fr., alcool Oly CLOT ig we (ou poly: basique, ou polphuarique)) Ger., mehratomiger (oder mehrbasischer, oder polyhydrischer) Alkohol. It., alcool pol i a to mico (o libasico, o politdrico). Sp., a. potiatémico (6 polibdsico, 6 pol i- Krarieo). Ana. derived from a hydrocarbon by replacing more than 1 atom of ny crogen by an equivalent amount of pyctoxy or formed by the substitution of a compound radicle for half the hydrogen in more than 1 molecule of water. [B.] See Diatomic a., Triatomic a., ete—Poly glucosic a. Fr., alcool polyglucosique. A hex atomic a. which may be porarded as derived from 2 or more molecules of glucose (C,H,20g) by the subtraction of a number of water molecules which is Ye by one than the number of molecules of glucose, They have, accordingly, the general formula NCgHy204—(0—1)HO = +y, and are designated as diglucosic, trigtucosic, etc., according as n= 2, 3, etc.; but only the diglucosic a’s are known. {B,2]—Primary a. Fr., alcool primaire. Ger., primdrer Alkohol. It., alcool primario. A monatomic a. in which the alcoholic hydroxy] is united to a carbon atom which itself is connected with only one other carbon atom, i. e., is united to the terminal carbon atom in the chain of radicles of which the hydrocarbon is composed. Such a's have evidently the general formula CH,(OH)—CH,— CH,—etc., or CnHan + 1.CH,(OH), and they may be regarded as methyl a. (carbinol) in which a single hydrogen atom is replaced by a univalent hydrocarbon. See CAR- BINOL. The primary a’s are converted by oxidizing agents into aldehydes (g. v.). [B, 4.|—Primary-secondary a. Fr., alcool primaire-second a ire, Ger., primär-sekundärer Alkohol. A diatomic a. in which one of the alcoholic hydrox yl molecules is united with a terminal carbon atom of the hydrocarbon chain, the other with a carbon atom which is itself combined with two other carbon atoms; e, 9., alpha oxy propylic a., CH,—CH(OH)—CH,(OH). [B, 4.]— Primary-tertiary a. Fr., alcool primaire-tertiaire. Ger., primédr-tertidrer Alkohol. A diatomic a. in which one of the alcoholic hydroxyl molecules is united with a terminal carbon atom of the hydrocarbon chain, the other with a carbon atom which is itself combined with three other carbon atoms; e. g., primary-tertiary isobutylene glycol, §F2>c(oH)-cH,om. [B, 4] — Pseudo-a. Fr., pseudo-alcool, alcool d'hydra tat i on. Ger., Pseudoalkohol. A variety of a. so called by Wurtz on account of the facility with which it can be decomposed into water and the corresponding olefine, and which may, therefore, be regarded -as the hydrate of that olefine, The term is particularly applied to the two secondary amyl a’s (propylmethylearbinol rettificato. Sp., a. rectificado. Ethyl a. concentrated by distillation. See ETHYL a.—Secondar, Fr., alcool second a ire. Ger., sekundärer Alkohol. It., alcool second a rio. An a. in which the carbon atom which is in combination with the alcoholic hydroxyl is also in direct combination with two other carbon atoms; e. ÿ. dimethyl carbinol, CHs — — CH. Such a's have the general formula CmHu — — CpHq, and may be regarded as derived from methy] a. (carbinol) by the substitution of two univalent hydrocarbons for 2 hydrogen atoms. See CarBINOL. The secondary a’s on oxidation give rise to the ketones (q. v.). [B,2,4.] See also Disecondary a. and Primary-secondary a—Secondary-tertiary a Fr., alcool second a ire-tertiaire. Ger., sekunddr-tertidrer Alkohol. A diatomic a. in which the 2 alcoholic hydroxy] molecules are united with 2 atoms of carbon which are themselves combined directly with 2 and with 8 other carbon atoms respectively; &. g., beta iscamylene glycol, Gy?>C(OH) — — CH. [B, 4.]— Standard a. Ethyl a. of a sp. gr. of 0°825 in which Sikes's hydrometer registers zero at 60° F. commercial term, [B,2.)—Stronger a, Lat., a. fortius. See ETHYL A.—Tertiary a. Fr., alcool tertiaire. Ger., tertidrer Alkohol. It., alcool terziario. An a. in which the carbon atom with which the alcoholic hydroxyl is united is also in direct combination with 3 other carbon atoms; e. g., trimethyl carbinol, GH c(OH) — CHs. Such a's have the general formula CHy” SEn C(OH) — Crh, and may be regarded as methyl a. (carbinol) in which 3 atoms of hydrogen are replaced by 3 univalent radicles. {B, 2,4.] See also Ditertiary @., Primary-tertiary a., Secondary tertiary a., and Carpi not.—Tetrabasic a., Tetracid a., Tetra hydric a., Tetratomic a. Fr., alcool tétrabasique (ou tétrahydrique, ou tétratomique). Ger., vier basis cher (oder tetrahydrischer, oder vier atom i ger) Alkohol. 1t., alcool tetrabasico (o tet raid rico, o tetra to mico). Sp., a. tetrabdsico (6 tetra hid rico, 6 tetratömico). Ana. derived from 4 molecules of water by replacement. of half the parogen by a quadrivalent hydrocarbon, or formed by the substitution of 4 molecules of hydroxy] for 4 atoms of hydrogen in a hydrocarbon. Erythrite is an ep of such an a. ib. 2,4.) —Thio-a. Fr., thio-alcool. Ger., Thioalkohol. See MERCAPTAN.— Triacid a., Triatomic a. Fr., alcool triacide (ou tri atom i que). Ger., dreiwerthiger (oder dreiatomiger) Alkokol. It., alcool tri a to mico, Sp.,a. tri a to mico. An a. formed by the substitution of a trivalent ‘hydrocarbon. for half the hydrogen in 8 molecules of water, or derived from a pyaiorar pod by re] lectes 3 atoms of hydrogen by 3 molecules of hydroxyl. Such a’s have the general formula CaHm- (OH)3, and Corie two cla es: 1. The glycerins, derived from hyrocarbons of the fatty series. 2. The triatomic phenols, derived from hydrocarbons of the aromatic series. The latter, however, are by many not included among the a's. The triatomic a’s are also called tribasic and trihydric because they contain 3 molecules of hydroxy] replaceable by acid radicles, and should theoretically give rise to 3 sets of saline derivatives (ethers) and to monobasic, dibasic, and tribasic acids. Few of these derivatives, however, are actually known. [B, 2, 4,6.] See also GLYCERIN and PHENOL—Tribasic a. Fr., alcool tribasique. Ger., dreibasischer Alkohol. It., atcool tribasico. Sp., a. tribdsico. Triatomic a.—Triglucosie a. Fr., alcool triglucosique. See pol up ucosic a—Trihydric a. Fr., alcool trihydrique. Ger., trihydrischer Atkohol. It., alcool triidrico. Sp., a. trihidrico. See Triatomic a.