Page:Encyclopædia Britannica, Ninth Edition, v. 14.djvu/208

 196 L A C L A C of the institutions have separate titles given to them either by the author or by a later editor. The first, De Falsa Religione, and the second, De Origine Erroris, attack the polytheism of heathendom, show the unity of the God of creation and providence, and try to explain how men have wandered from truth into polytheistic error. The third book, De Falsa Sapientia, describes and criticizes the various systems of prevalent philosophy, showing how b.i33less and contradictory they are. The fourth book, De Vera Sapientia et Eeligione, insists upon the inseparable union of true wisdom and true religion, and maintains that this union is made real in the person of Christ, The fifth book, De Justitia, maintains that true righteousness is not to be found apart from Christianity, and that it springs from piety which consists in the knowledge of God. The sixth book, De Vero Cultu, describes the true worship of God, which is righteousness, and consists chiefly in the exercise of Christian love towards God and man. The seventh book, De Vita Beata, discusses, among a variety of subjects, the chief good, immortality, the second advent, and th 3 resurrection. Jerome tells us that Lactantius wrote an epitome of these Institutions, and such a work was discovered in the royal library at Turin in 1712 by C. M. Pfaff; it is doubtful, however, whether this MS. is the epitome of Lactantius. Besides the Institutions, Lactantius wrote a treatiss, De Ira Dei, addressed to one Donatus and directed against the Epicurean philosophy; an argument for the wisdom and goodness of God as exhibited in the creation and preservation of the world, De Opificio Dei sive de Formatione Ilominis; and a very celebrated treatise De Mortibus Persecutorum, which describes God s judgments on the persecutors of his church from Nero to Diocletian, and has served as a model for numberless subsequent writings of a like nature. De Mort. Persccut. is not included in the earlier editions of Lactantius; it was discovered and printed by Baluze in 1679. Many critics do not believe it to be the work of our author, and ascribe it to an unknown Lucius Cagcilius (see the work of Ebert above quoted). Jerome speaks of Lactantius as a poet, and several poems have been attributed to him : De Pkenice, Symposium, De Pascha ad Felicem Episcopum, and De Passione Domini. It is extremely probable that all these are the productions of a much later age. MS3. of Lactantius are very numerous; a very complete catalogue of thes3 and of the earlier printed editions will be found in Le Brim and Lenglet Dufresnoy s edition, 2 vols. Paris, 1748. The best editions besides Dufresnoy s are those of Walch, Leipsic, 1715; of Biinemann, Leipsic, 1739; and in Migne s Patrotogia Latina, vols. vi. and vii. A new edition is promised in the Vienna Corpus Script. Eccles. Latin. LACTIC ACID, a chemical term, which, though origin ally invented to designate the particular acid contained in sour milk, has now, through the discovery of other acids isomeric with and very similar to that acid, acquired a generic, in addition to its original specific, meaning. 1. Lactic Acid properly so called, Fermentation Lactic Acid, Ethylidene Lactic Acid. Scheele (Transactions of Stockholm Acad., 1780) was the first to isolate this acid (from sour milk) and establish its individuality. About twenty-four years later Bouillon Lagrange, and, independ ently of him, also Fourcroy and Vauquelin maintained that Scheele s new acid was nothing but impure acetic. But this notion was combated by Berzelius, and finally refuted (in 1832) by Liebig and Mitscherlich, who by the elementary analyses of lactates proved the existence of this as a distinct acid. Iu the article FERMENTATION (vol. ix. p. 97) it is explained how lactic acid is produced from milk-sugar and from ordinary glucose by &quot;lactic fermentation.&quot; The most convenient process for the preparation of the acid is Bensch s. A solution of &quot;invert- sugar&quot; (see vol. ix. p. 96) is produced by dissolving 6 parts of cane-sugar and T i th part of tartaric acid in 35 parts of boiling water and allowing to stand for tvo days. There is then added Tgth part of. foul cheese, 8 parts of sour milk, and 2^ parts of carbonate of zinc, and the mixture kept at 40 to 45 C. for eight to ten days. The sugar, C B H 12 6, ferments into lactic acid, C 3 H 6 3, which, by the carbonate present, is converted into lactatc of zinc. But part of the lactate is invariably lost through &quot; butyric fermentation &quot; with evolution of hydrogen, which latter converts part of the sugar into mannite, C 6 H ]4 6. The fermented liquid is heated to boiling, strained clear, and allowed to cool, when the lactate of zinc separates out in crystalline crusts, which are purified by recrystallization from hot water. The free acid is obtained by decom posing the hot aqueous solution of the salt with sulphuretted hydro gen and filtering off the sulphide of zinc. The filtrate is evaporated on a water bath to a syrup, which is treated with ether. JVIanuite and other impurities remain, and the acid passes into the nitrate, from which the ether is easily expelled by distillation, and subsequent evaporation in an open basin. What ultimately remains is a thick colourless syrup, which, in ordinary chemical parlance, goes as lactic acid, although it is at best only an approximation to the hydrate, C 3 H 6 3 .H 2 0. The extra H 2 is easily enough removed by continued evaporation, but no portion of it can be thus got rid of without the acid C 3 H 6 3 itself suffering dehydration into lactic anhydride, C 6 H 10 5, and lactidc, C 6 H 8 4 , by successive subtractions of H 2 from 2C 3 H 6 3. The behaviour of lactic acid solution to basic reagents and of the acid itself to alcohols (in the presence of dehy- drators) is strictly that of a monobasic acid C 3 H O 3; i.e., so much lactic is strictly equivalent to one molecule of acetic acid, and as the latter is proved to be CH 3 .COOH, lactic acid must be assumed to be (C 2 H 5 0) COOH. But the radicle C 2 H 5 O (unlike the CH 3 of acetic acid) still contains one hydrogen atom, which, although not replace able by metals, can be replaced by acid radicles such as acetyl C.,ILjO or, conjointly with the oxygen atom, by Cl,Br,I. Thus, for instance, lactic ether, (C 2 H 5 O)COOC 2 H-, when treated with chloride of acetyl, C 2 H 3 O.C1, gets con verted into acetyl-lactic ether,[C 2 H 4 (C 2 H 3 O)0]COO(C 2 H 5 ), with formation of hydrochloric acid. By the action of hydriodic acid the same H conjointly with the O of the radicle is replaced by iodine with formation of water. In a word, lactic acid, besides being an acid analogous to, for instance, acetic acid, CH 3 COOH, is at the same time an alcohol analogous to ordinary spirit of wine, C 2 H fj .OH, as shown by the formula HO C 2 H 4 COOH. This two fold character of our substance explains the readiness with which it passes into anhydrides. Lactic acid the acid acts upon lactic acid the alcohol; the replaceable H in the former unites with the OH of the latter, and the two rests combine into an ether which is lactic anhydride. Thus : (CJi 4 OH) COO Lactic anhydride. The slanting lines show the mode of combination after the reaction. The anhydride, as we see, still contains an OH and COOH, and a repetition of the group within its molecule leads to lactide, C H 8 4. This latter body- could be presumed to be formed from one molecule of lactic acid : HO(C S H 4 )COOH == (C 2 II 4 )COO + H. OH; but the vapour density determination proves the molecular weight to be in accordance with the larger formula C 6 H 8 O 4. Admitting, as well we may, that lactic acid is a compound of COOH and OH with C 2 H 4, what is this C 2 H 4 itself? This question has been satisfactorily answered. When lactic acid is distilled rapidly, it breaks up into formic acid, H. COOH, and aldehyde, (CH 3 )(CO)H. Conversely when aldehyde is treated with hydro cyanic acid and muriatic acid it is converted into lactic acid, in two steps, thus : (1) the C = in the aldehyde combines with the (NC)H, the H going to the and the (NC) by its C to the C, to form the group (NC) C H; and (2) the NC of this group, by the action of the water, gets converted into a COOH, with formation of NH 3, which combines with the muriatic acid. NO + 2H.,0 = NH, + COOH. The (CH 3 ) and H in the original aldehyde retain their places, so that what we obtain ultimately must be and this consequently is the structure of lactic acid. The radicle