صور الصفحة
PDF

have been incited to try alkaline liquids as electrolytes. Many attempts have been made to construct accumulators in this way, though with only moderate success. The Lalande-Chaperon, Desmazures, Waddell-Entz and Edison are the chief cells. T. A. Edison’s cell has been most developed, and is intended for traction work. He made the plates of very thin sheets of nickelplated steel, in each of which 24 rectangular holes were stamped, leaving a mere framework of the metal. Shallow rectangular pockets of perforated nickel-steel were fitted in the holes and then burred over the framework by high pressures. The pockets contained the active material. On the positive plate this consisted of nickel peroxide mixed with flake graphite, and on the negative plate of finely divided iron mixed with graphite. Both kinds of active material were prepared in a special way. The graphite gives greater conductivity. The liquid was a 20% solution of caustic I potash. During discharge the iron was oxidized, and the nickel reduced to a lower state of oxidation. This change was reversed during charge. Fig. 24 shows “ the general features.

The chief results obtained by European experts showed that the EJLF. was 11,3 '- volt, with a transient higher value following charge. A cell weighing 17-8 lb had a resistance of 0-0013 ohm, and an output at 60 amperes of no watt-hours, or at 120 amperes of 177 watt-hours. Another and improved cell weighing 12-7 1b gave 14-6 watt-hours per pound of cell at a zo-ampere rate, and 13-5 watt-hours per pound at a. 60ampere rate. The cell could be charged and discharged at almost any rate. A full charge could be given in 1 hour, and it' would stand a discharge rate of 200 amperes (Journ. Inst. Elec. Eng, 1904, pp. 1-36).

Subsequently Edison found some degree of falling-ofl in capacity, due to an enlargement of the positive pockets by pressure of gas. Most of the faults have been overcome by altering the form of the pocket and replacing the graphite by a metallic conductor in the form of flakes.

REFERENCES.—-G- Planté, Recherche: sur l'électrtcité (Paris, 1879); Gladstone and Tribe, Chemistry of Secondary Batteries (London, 1884); Reynier, L'Accumulateur voltaique (Paris, 1888); Heim, Die Akkumulatoren (Berlin, 1889); Hoppe, Die Akk. far Elektricildt (Berlin, 1892); Schoop, Handbuch filr Akk. (Stutt art, 1898); Sir E. Frankland, “ Chemistry of Storage Batteries," g’rac. Ray. 500., 1883; Re nier, Jour. Sac. Fran. de Phys, 188 ; Heim, “U. d. Einfluss er Siiuredichte auf die hapazitat der A k.," Elek. Zeits., 1889; Kohlrausch and Heim, " Ergebnisse von Versuchen an Akk. filr Sistionsbetrieb," Elek. Zeits., 1889; Darrieus, Bull. Soc. Intern. .9 later (London, 1906) ; Sir D. Salomons, Management of Acoumulators (London, 1906): E. J. Wade, Secondary Batteries (London, 1 or); L. Jumau, LesAccumulateur: électrigues (Paris, 1904). (W. '1‘.)

ACCURSIUS (Ital. ACCORSO) , FRANCISCUS (1 182—1 26o),Italian jurist, was born at Florence about 1182. A pupil of A20, he first practised law in his native city, and was afterwards appointed professor at Bologna, where he had great success as a teacher. He undertook the great work of arranging into one body the almost innumerable comments and remarks upon the Code, the Institutes and Digests, the confused dispersion of which among the works of different writers caused much obscurity and contradiction. This compilation, bearing the title Glossa ordinaria or magistratis, but usually known as the Great Gloss, though written in barbarous Latin, has more method than that of any preceding writer on the subject. The best edition of it is that of Denis Godefroi (1549—1621), published at Lyons in 1589, in 6 vols. folio. When Accursius was employed in this work, it is said that, hearing of a similar one proposed

[graphic]

F10. 24.——Edison Accumulator.

and begun by Odofred, another lawyer of Bologna, he feigned

[ocr errors]
[graphic]

indisposition, interrupted his public lectures, and shut himself up, till with the utmost expedition he had accomplished his design. Accursius was greatly extolled by the lawyers of his own and the immediately succeeding age, and he was even called the idol of jurisconsults, but those of later times formed a much lower estimate of his merits. There can be no doubt that he disentangled the sense of many laws with much skill, but it is equally undeniable that his ignorance of history and antiquities. often led him into absurdities, and was the cause of many defects in his explanations and commentaries. He died at Bologna in 1260. His eldest son Franciscus (1225—1293), who also filled the chair of law at Bologna, was invited to Oxford by King Edward I., and in 1275 or 1276 read lectures on law in the university.

ACCUSATION (Lat. accusatio, accusare, to challenge to a causa, a suit or trial at law), a legal term signifying the charging of another with wrong-doing, criminal or otherwise. An accusation which is made in a court of justice during legal proceedings is privileged (see PRIVILEGE), though, should the accused have been maliciously prosecuted, he will have a right to bring an action for malicious prosecution. An accusation made outside a. court of justice would, if the‘ accusation were false, render the accuser liable to an action for defamation of character, while, if the, accusation be committed to writing, the writer of it is liable to indictment, whether the accusation be made only to the party accused or to a third person. A threat or conspiracy to accuse another of a crime or of misconduct which does not

amount to a crime for the purpose of extortion is in itself

indictable.

ACCUSATIVE (Lat. aceusativus, sc. easus, a translation of the Gr. ainanxr) 118mg the case concerned with cause and effect, from atria, a cause), in grammar, a case of the noun,

denoting primarily the object of verbal action or the destination

of motion.

ACE (derived through the Lat. as, from the Tarentine form of the Gr. sis), the number one at dice, or the single point on a die or card; also a point in the score of racquets, lawntennis, tennis and other court games.

ACELDAMA (according to Acts i. 19, “ the field of blood ”), the name given to the field purchased by Judas Iscariot with the money he received for the betrayal of Jesus Christ. A different version is given in Matthew xxvii. 8, where Judas is said to have cast down the money in the Temple, and the priests who had paid it to have recovered the pieces, with which they bought “the potter’s field, to bury strangers in.” The MS. evidence is greatly in favour of a form Aceldamach. This would seem to mean “ the field of thy blood,” which is unsuitable. Since, however, we find elsewhere one name appearing as both Sirach and Sira (ch=s), Aceldamach may ‘ be another form of an original Aceldama (not! 5,10,), the “field of blood.” A. Klostcrmann,

[ocr errors]

cemetery (Prableme im A Posteltexte, 1-8, 1883), an explanation which fits in well with the account in Matthew xxvii. The traditional site (now Hak el-Dum), S. of Jerusalem on the N.E. slope of the “Hill of Evil Counsel” (Jebel Deir Abu Tor), was used as a burial-place for Christian pilgrims from the 6th century AD. till as late, apparently, as 1697, and especially in the time of the Crusades. Near it there is a very ancient chamelhouse, partly rock-cut, partly of_ masonry, said to be the work of Crusaders. . _

ACENAPHTHENE, CnHio, a hydrocarbon isolated from the fraction of coal-tar boiling at 260°—27o° by M. P. E. Berthelot, who, in conjunction with Bardy, afterwards synthesized it from a-ethyl naphthalene (Ann. Chem. Phys, 1873, vol. xxix.). It forms white needles (from alcohol), melts at 95° and boils at 278°. Oxidation gives inaphthalic acid (1-8 naphthalene dicarboxylic acid).

Acenaphthalene, C12 H;, a hydrocarbon crystallizing in yellow tables and ‘obtained by passing the vapour of acenaphthene over heated litharge. Sodium amalgam reduces it to acenaphthene; chromic acid oxidizes it to naphthalic acid.

ACEPHALI (from 6-, privative, and xedmllfi, head), a term applied to 'several sects as having no head or leader; and in particular to a strict monophysite sect that separated itself, in the end of the 5th century, from the rule of the patriarch of Alexandria (Peter Mongus), and remained “ without king or bishop ” till they were reconciled by Mark I. (799-819).l The term is also used to denote clerici vagrantes, i.e. clergy without title or benefice, picking up a living anyhow (cf. Hinschius i. p. 64). Certain persons in England during the reign of King Henry I. were called Acephah' because they had no lands by virtue of which they could acknowledge a superior lord. The name is also given to certain legendary races described by ancient naturalists and geographers as having no heads, their mouths and eyes being in their breasts, generally identified with Pliny’s Blemmyae.

ACEPHALOUS, headless, whether literally or metaphorically, leaderless. The word is used literally in biology; and metaphorically in prosody or grammar for a verse or sentence with a. beginning wanting. In zoology, the mollusca are divided into cephalous and acephalous (Acephala), according as they have or have not an organized part of their anatomy as the seat of the brain and special senses. The Acephala, or Lamellibranchiata (q.v.), are commonly known as bivalve shell~fish. In botany the word is used for ovaries not terminating in a stigma. Acephalocyst is the name given by R. T. H. Laennec to the hydatid, immature or larval tapeworm.

ACERENZA (anc. Acerunlia), a town of the province of Potenza, Italy, the seat of an archbishop, 15% m. N.E. of the station of Pietragalla, which is 9 m. N.W. of Potenza by rail, 2730 ft. above sea-level. Pop. (root) 4499. Its situation is one of great strength, and it has only one entrance, on the south. It was occupied as a colony at latest by the end of the Republic, and its importance as a fortress was specially appreciated by the Goths and Lombards in the 6th and 7th centuries. It has a fine Norman cathedral, upon the gable of which is one of the best extant busts of Julian the Apostate.

ACEROSE (from Lat. acus, needle, or acer, sharp), needleshaped, a term used in botany (since Linnaeus) as descriptive of the leaves, c.g., of pines. From Lat. acus, chaff, comes also the distinct meaning of “ mixed with chaff.”

ACERRA, a town and episcopal see of Campania, Italy, in the province of Caserta, 9 m. N.E. from Naples by rail. Pop. (1901) 16,443. The town lies on the right bank of the Agno, which divides the province of Naples from that of Caserta, 90ft. above the sea, in a fertile but'somewhat marshy district, which in the middle ages was very malarious. The ancient name (A cerrae) was also home by a town in Umbria and another in Gallia Transpadana (the latter now Pizzighettone on the Adda, 13 m. W.N.W. of Cremona). It became a city with Latin rights in 332 13.0. and later a municipium. It was destroyed by Hannibal in 216 B.C., but restored in '210; in 90 13.0. it served as the Roman headquarters in the Social war, and was successfully held against the insurgents. appears to have suffered much from floods of the river Clanis. Under the Empire we hear no more of it, and no traces of antiquity, beyond inscriptions, remain.

ACBRRA, in Roman antiquity, a small box or pot for holding incense, as distinct from the turibulum (thurible) or ccnser in which incense was burned. The name was also given by the Romans to a little altar placed near the dead, on which incense was offered every day till the burial. Iri ecclesiastical Latin the -term acerra is still applied to the incense boats used in the Roman ritual.

ACETABULUM, the Latin word for a vinegar cup, an ancient Roman vessel, used as a liquid measure (equal to about half a gill); it is also a word used technically in zoology, by analogy for certain cup-shaped parts, e.g. the suckers of a mollusc, the socket of the thigh-bone, &c.; and in botany for the receptacle of Fungi.

ACETIC ACID (acidum acelfcum), CHyCO-ZH, one of the most important organic acids. It occurs naturally in the juice of

‘ See Gibbon. ch. xlvii. (vol. v. p. 129 in Bury": ed.).

It received a colony under Augustus, but,

[graphic]

many plants, and as the esters of n-hexyl and n-octyl alcohols in the seeds of Heracleum gigonleum, and in the fruit of H eracleum sphondylium, but is generally obtained, on the large scale, from the oxidation of spoiled wines, or from the destructive distillation of wood. In the former process it is obtained in the form of a dilute aqueous solution, in which also the colouring matters of the wine, salts, &c., are dissolved; and this impure acetic acid is what we ordinarily term vinegar (q.v.). Acetic acid (in the form of vinegar) was known to the ancients, who obtained it by the oxidation of alcoholic liquors. Woodvinegar was discovered in the middle ages. Towards the close of the 18th century, A. L. Lavoisier showed that air was necessary to the formation of vinegar from alcohol. In 1830 J. B. A. Dumas converted acetic acid into trichloracetic acid, and in 1842 L. H. F. Melsens reconverted this derivative into the original acetic acid by reduction with sodium amalgam. The synthesis of trichloracetic acid from its elements was accomplished in 1843 by H. Kolbe; this taken in conjunction with Melsens's observation provided the first synthesis of acetic acid. Anhydrous acetic acid—glacial acetic acid—is a leafy crystalline mass melting at 16-7° C., and possessing an exceedingly pungent smell. It boils at 118°, giving a vapour of abnormal specific gravity. It dissolves in water in all proportions with at first a contraction afterwards an increase in volume. It is detected by heating with ordinary alcohol and sulphuric acid, which gives rise to acetic ester or ethyl acetate, recognized by its fragrant odour; or by heating with arsenious oxide, which forms the pungent and poisonous cacodyl oxide. It is a monobasic acid, forming one normal and two acid potassium salts, and basic salts with iron, aluminium, lead and copper. Ferrous and ferric acetates, are used as mordants; normal lead acetate is known in commerce as sugar of lead (q.v.); basic copper acetates are known as verdigris (q.v.).

Pharmacology and Therapeutics—Glacial acetic acid is occasionally used as a caustic for corns. The dilute acid, or vinegar, may be used to bathe the skin in fever, acting as a pleasant refrigerant. Acetic acid has no valuable properties for internal administration. Vinegar, however, which contains about 5 % acetic acid, is frequently taken as a cure for obesity, but there is no warrant for this application. Its continued employment may, indeed, so injure the mucous membrane of the stomach as to interfere with digestion and so cause a morbid and dangerous reduction in weight. .

The acetates constitute a valuable group of medicinal agents, the potassium salt being most frequently employed. After absorption into the blood, the acetates are oxidized to carbonates, and therefore are remote alkalies, and are administered whenever it is desired to increase the alkalinity of the blood or to reduce the acidity of the urine, without exerting the disturbing influence of alkalies upon the digestive tract. The citrates act in precisely similar fashion, and may be substituted. They are somewhat more pleasant but more expensive. '

ACETO-ACETIC ESTER, CQHIOOQ or CHg'CO'CHg'COOCQHs, a chemical substance discovered in 1863 by A. Geuther, who showed that the chief product of the action of sodium on ethyl acetate was a sodium compound of composition CH90,Na, which on treatment with acids gave a colourless, somewhat oily liquid of composition ConOa. E. Frankland and B. F. Duppa in 1865 examined the reaction and concluded that Geuther’s sodium salt was a derivative of the ethyl ester of acetone carboxylic acid and possessed the constitution CliaCO-CHNa-COOCsz. This view was not accepted by Geuthcr, who looked upon his compound CQHMO, as being an acid. J. Wislicenus also investigated the reaction very thoroughly and accepted the Frankland-Duppa formula (Annalen, 1877, 186, p. 163; r877, 190. p- 151).

The substance is best prepared by drying ethyl acetate over calcium chloride and treating it with sodium wire, which is best introduced in one operation; the liquid boils and is then heated on a water bath for some hours, until the sodium all dissolves. After the reaction is completed, the liquid is acidified with dilute sulphuric acid (1:5) and then shaken with salt solution, separated from the salt solution, washed, dried and fractionated. The portion boiling between 175° and 185°C. is redistilled. The yield amounts to about 30% of that required by theory. A. Ladenburg and J. A. Wanklyn have shown that pure ethy acetate free from alcohol will not react with sodium to produce aceto-acetic ester. L. Claisen, whose views are now accepted, studied the reactions of sodium ethylate and showed that if sodium ethylate be used in place of sodium in the above reaction the same result is obtained. He explains the reactions thus: /0 ' Na CH=-C<OC H +NaOC,Ht=CHJ-C<OC,H5, ’ ‘ OC,Hi

this reaction being followed by
/CM H\
\_\OC2H5+ Hb=2C2H59H+ \

Oc'lHS CHs-C(0Na) :CH-COOCJL; and on acidification this last substance gives aceto-acetic ester. Aceto-acetic ester is a colourless liquid boiling at 181°C; it is slightly soluble in water, and when distilled undergoes some decomposition forming dehydracetic acid CAP-30,. It undoubtedly contains a keto-group, for it reacts with hydrocyanic acid, hydroxylamine, phenylhydrazine and ammonia; sodium bisulphite also combines with it to form a crystalline compound, hence it contains the grouping CH,-CO—. J. Wislicenus found that only one hydrogen atom in the —CH2 — group is directly replaceable by sodium, and that if the sodium be then replaced by an alkyl group, the second hydrogen atom in the group can be replaced in the same manner. These alkyl substitution products are important, for they lead to the synthesis of many organic compounds, on account of the fact that they can be hydrolysed in two different ways, barium hydroxide or dilute sodium hydroxide solution giving the socalled ketone hydrolysis, whilst concentrated sodium hydroxide gives the acid hydrolysis.

Kelone hydrolysis:—

CH3'CO‘C(XY)'COQC!H5%CH3'CO'CH(XY)+C2H60H+C02i

Acid hydrolysis:— ’ CH,-CO-C(XY)-C02C2H5+CHa-C01H+CthOH+CH(XY)-COOH; (where X and Y =alkyl groups).

Both reactions occur to some extent simultaneously. Acetoacetic ester is a most important synthetic reagent, having been used in the production of pyridines (qua), quinolines (q.v.), pyrazolones, furfurane (q.v.), pyrrols (q.v.), uric acid (q.v.), and many complex acids and ketones.

For a discussion as to the composition, and whether it is to be regarded as possessing the “ keto " form CHrCO-Cl-l1-COOC2H5 or the “enol” form CH;-C(OH) : CH'COOCgHs, see lSOMERrsM, and also papers by J. Wislicenus (A nn., 1877, 186, p. :63; 1877, I 0, p. 257), A. Michael (Journ. Prak. Chem, 1887, [2] 7, p. 473), L. norr (Arm. I886, 238, p. 147), W. H. Perkin, senr. (foam. of Chem. 500., 1892, 61, p. 800) and J. U. Nef (Ann., 1891, 266, p. 70; 1892, 270, pp- 289. 333; I893, 276, 11212)

ACETONE, or DIMETHYL Karena, CHa-CO CH3, in chemistry, the simplest representative of the aliphatic ketones. .a It is present in very small quantity in normal urine, in the blood, and in larger quantities in diabetic patients. It is found among the products formed in the destructive distillation of wood, sugar, cellulose, &c., and for this reason it is always present in crude wood spirit, from which the greater portion of it may be recovered by fractional distillation. On the large scale it is prepared by the dry distillation of calcium acetate (CPLC01)2Ca= CaCOZ+CH3COCH;. E. R. Squibb (Journ. Amer. Chem. Soc., 1895, 17, p. 187) manufactures it by passing the vapour of acetic acid through a rotating iron cylinder containing a mixture of pumice and precipitated barium carbonate, and kept at a temperature of from 500° C. to 600° C. The mixed vapours of acetone, acetic acid and water are then led through a condensing apparatus so that the acetic acid and water are first condensed, and then the acetone is condensed in a second vessel. The barium carbonate used in the process acts as a contact substance, since the temperature at which the operation is carried out is always above the decomposition point of barium acetate.

[ocr errors]
[graphic]

Crude acetone may be purified by converting it into the crystalline sodium bisulphite compound, which is separated by filtration and then distilled with sodium carbonate.

[ocr errors]

CH.
It is then dehydrated and redistilled.

Acetone is largely used in the manufacture of cordite (17.0.). For this purpose the crude distillate is redistilled over sulphuric acid and then fractionated. ' ‘

Acetone is a colourless mobile liquid 'of pleasant smell, boiling at 56-53°C., and hasaspecific gravity o-'819(o°/4°C.). Iti's readily soluble in water, alcohol, ether, &c. In addition to its application in the cordite industry, it is used in the manufacture of chloroform (q.'v.) and sulphonal, and as a solvent. It forms a hydrazone with phenyl hydrazine, and an oxime with hydroxylamine. Reduction by sodium amalgam converts it into iso— propyl alcohol; oxidation by chromic acid gives carbon dioxide and acetic acid. With ammonia it reacts to form di- and triacetoneamines. It also unites directly with hydrocyanic acid to form the nitrile of a-oxyisobutyric acid.

By the action of various reagents such as lime, caustic potash, hydrochloric acid, &c., acetone is converted into condensation products, mesityl oxide CsHmO, phorone CQHHO, &c., being formed. On distillation with sulphuric acid, it is converted into mesitylene C9H12(symmetrical ‘trimethyl benzene). Acetone has also been used in the artificial production of indigo. In the presence of iodine and an alkali it gives iodoform. Acetone has been employed medicinally in cases of dyspnoea. With potassium iodide, glycerin and water, it forms the preparation spirone, which has been used as a spray inhalation in paroxysmal sneezing and asthma.

ACETOPHENONE, or PHENYL-METnYL KETONE, Cal-LO or CGHQCO‘CHQ, in chemistry, the simplest representative of the class of mixed aliphatic-aromatic ketones. It can be prepared by distilling a mixture of dry calcium benzoate and acetate, Ca(O2CC6H5)2+(CH3CO;)-_-Ca=2CaC01+2C6H5CO-CH3, OI' condensing benzene with acetyl chloride in the presence of anhydrous aluminium chloride (C. Friedel and J. M. Crafts), CGHs-‘l— CH,COCl =HC1+C5H5COCH;. It crystallizes in colourless plates melting at 20°C. and boiling at 202°C; it is insoluble in water, but readily dissolves in the ordinary organic solvents. It is reduced by nascent hydrogen to the secondary alcohol CQHa-CH-OH-CH; phenyl-methyl-carbinol, and on oxidation forms benzoic acid. On the addition of phenylhydrazine it gives a (phenylhydrazone, and with hydroxylamine furnishes an oxime égZ>C=N-OH melting at 59°C. This oxime undergoes a peculiar rearrangement when it is dissolved in ether and phosphorus pentachloride is added to the ethereal solution, the excess of ether distilled 05 and water added to the residue being converted into the isomeric substance acetanilide, QHENHCOCHK, a behaviour shown by many ketoximes and known as the Beckmann change (see Berichte, 1886, 19, p. 988). With sodium ethylate in ethyl acetate solution it forms the sodium derivative of benzoyl acetone, from which benzoyl acetone, C5H5'CO'CH2'CO'CH3, can be obtained by acidification with acetic acid. When heated with the halogens, acetophenone is substituted in the aliphatic portion of the nucleus; thus bromine gives phenacyl bromide, QH5CO'CHzBl'. Numerous derivatives of acetophenone have been prepared, one of the .most important being orthoaminoacetophenone, N Hz‘CgI‘IfCO'Cm, which is obtained by boiling orthoaminophenylpropiolic acid with water. It is a thick yellowish oil boiling between 242° C. and 250° C. It condenses with acetone in the presence of caustic soda to a quinoline. Acetonyl-acetophemme, C5H5-CO-CH1-CHg-CO-CH3, is produced by condensing phenacyl bromide with sodium acetoacetate with subsequent elimination of carbon dioxide, and on dehydration gives aa-phenyl-methyl-furfurane. - Oxazoles (q.v.) are produced on condensing phenacyl bromide with acid-amides (M. Lewy, Berichte, r887, 20, p. 2578). K. L. Paal has also obtained pyrrol derivatives by condensing acetophenone-acetoacetic-ester with substances of the type NHaR.

ACETYLENE, klumene or ethine, a gaseous compound of carbon and hydrogen, represented by the formula. CgHg. It is a colourless gas, having a density of 0-92. When prepared by the action of water upon calcium carbide, it has a very strong and penetrating odour, but when it is thoroughly purified from sulphuretted and phosphuretted hydrogen, which are invariably present with it in minute traces, this extremely pungent odour disappears, and the pure gas has a not unpleasant ethereal smell. ' It can be condensed into the liquid state by cold or by pressure, and experiments, by G. Ansdell show that if the gas be subjected to a pressure of 21- 5 3 atmospheres at a temperature of 0° C., it is converted into the liquid state, the pressure needed increasing with the rise of temperature, and decreasing with the lowering of the temperature, until at .—82° C. it becomes liquid under ordinary atmospheric pressure.- The critical point of the gas is 37° C., at which temperature a pressure of 68 atmospheres is required for liquefaction. The properties of liquid and solid acetylene have been investigated by D. McIntosh (Jour. Chem. 500., Abs., 1907, i. 4 58); A great future was expected from its use in the liquid state, since a cylinder fitted with the necessary reducing valves would supply the gas to light a hOuse for a considerable period, the liquid occupying about 1th the volume of the gas, but in the United States and on the continent of Europe, where liquefied acetylene was made on the large scale, several fatal accidents occurred owing to its explosion under not easily explained conditions. .As a result of these accidents M. P. E. Berthelot and L. 1]. G. Vieille made a series of valuable researches upon the explosion of acetylene under various conditions. They found that if liquid acetylene in a steel bottle be heated at one point by a platinum wire raised to a red heat, the whole mass decom— poses and gives rise to such tremendous pressures that no cylinder would be able to withstand them. These pressures varied from 7 1,000 to 100,000 lb. per square inch. They, moreover, tried the cflect of shock upon the liquid, and found that the repeated dropping of the cylinder from a height of nearly 20 feet upon a. large steel anvil gave no explosion, but'that when the cylinder was crushed under a heavy blow the impact was followed, after a short interval of time, by an explosion which was manifestly due to the fracture of the cylinder and the ignition of the escaping gas, mixed with air, from sparks caused by the breaking of the metal. A similar explosion will frequently follow the breaking in the same way of a cylinder charged with hydrogen at a high pressure. Continuing these experiments, they found that in acetylene gas under ordinary pressures» the decomposition brought about in one portion of the gas, either by heat or the firing in it of a small detonator, did not spread far beyond the point at which the decomposition started, while if the acetylene was compressed to a pressure of more than 30 lb on thesquare inch, ,the decomposition travelled throughout the mass and became in reality detonation. These results showed clearly that liquefied acetylene was far too dangerous for general introduction for domestic purposes, since, although the occasions would be rare in which the requisite temperature to bring about detonation would be reached, still, if this point were attained, the results would be of a most disastrous character. The fact that several accidents had already happened accentuated the risk, and in

Physical properties.

Great Britain the storage and use of liquefied acetylene are

prohibited.

When liquefied acetylene is allowed to escape from the cylinder in which it is contained into ordinary atmospheric pressure, some of the liquid assumes the gaseous condition with such rapidity as to cool the remainder below the temperature of —-90° 11., and convert it into a solid snow-like mass.

Acetylene is readily soluble in water, which at normal temperature and pressure takes up a little more than its own volume of the gas, and yields a solution giving a purple-red precipitate with ammoniacal cuprous chloride and a white precipitate with silver nitrate, these precipi~ tates consisting of acetylides of the metals. The solubility of the gas in various liquids, as given by different observers, is— ., -_ . , , ,

[ocr errors]
[graphic]
[merged small][ocr errors]

It will be seen from this table that where it is desired to collect and keep acetylene over a liquid, brine, Le. water saturated with salt, is the best for the purpose, but in practice it is found that, unless water is agitated with acetylene, or the gas bubbled through, the top layer soon gets saturated, and the gas then dissolves but slowly. The great solubility of acetylene in acetone was pointed out by G. Claude and A. Hess, who showed that acetone will absorb twenty-five times its own volume of acetylene at a temperature of 15° C. under atmospheric pressure, and that, providing the temperature is kept constant, the liquid acetone will go on absorbing acetylene at the rate of twentyfive times its own volume for every atmosphere of pressure to which the gas is subjected.

At first it seemed as if this discovery would do away with all the troubles connected with the storage of acetylene under pressure, but it was soon found that there were serious difficulties still to be overcome. The chief trouble was that acetone expands a small percentage of its own volume while it is absorbing acetylene; therefore it is impossible to fill a cylinder with acetone and then force in acetylene, and still more impracticable only partly to fill the cylinder with acetone, as in that case the space above the liquid would be filled with acetylene under high pressure, and would have all the disadvantages of a cylinder containing compressed acetylene only. This difficulty was overcome by first filling the cylinder with porous briquettes and then‘soaking them with a fixed percentage of acetone, so that after allowing for the space taken up by the bricks the quantity of ‘ acetone soaked into the brick will absorb ten times the normal volume of the cylinder in acetylene for every atmo~ sphere of pressure to which the gas is subjected, whilst all danger of explosion is eliminated.

This fact having been fully demonstrated, acetylene dissolved in this way was exempted from the Explosives Act, and consequently upon this exemption a large business has grown up in the preparation and use of dissolved acetylene for lighting motor omnibuses, motor cars, railway carriages, lighthouses, buoys, yachts, &c., for which it is particularly adapted.

Acetylene was at one time supposed to be a highly poisonous gas, the researches of A. Bistrow and O. Liebreich having apparently shown that it acts upon the blood in the same way as carbon monoxide to form a stable compound. Very extensive experiments, however, made by Drs N. Grchant, A. L. Brociner, L. Crismer, and others, all con— clusively show that acetylene is much less toxic than carbon monoxide, and indeed than coal gas.

'When acetylene was first introduced on a commercial scale grave fears were entertained as to its safety, it being represented that it had the power of combining with certain metals, more especially copper and silver, to form acetylides of a highly explosive character, and that even with coal gas, which contains less than 1%, such copper compounds had been known to be formed in cases where the gas-distributing mains were composed of copper, and that accidents had happened from this cause. It was therefore predicted that the introduction of acetylene on a large scale would be followed by numerous accidents unless copper and its alloys were rigidly excluded from contact with the gas. These fears have, however, fortunately proved to be unfounded, and ordinary gas fittings can be used with perfect safety with this gas.

Acetylene has the property of inflaming spontaneously when brought in contact with chlorine. If a few pieces of carbide be dropped into saturated chlorine water the bubbles of gas take

Poisonous properties.

Chemical proportion.

fire as they reach the surface, and if a jet of acetylene be passed up into a bottle of chlorine it takes fire and burns with a heavy red flame, depositing its carbon in the form of soot. If chlorine be bubbled up into a jar of acetylene standing over water, a violent explosion, attended with a flash of intense light and the deposition of carbon, at once takes place. When the gas is kept in a small glass holder exposed to direct sunlight, the surface of the glass soon becomes dimmed, and W. A. Bone has shown that when exposed for some time to the sun’s rays it undergoes certain polymerization changes which lead ,to the deposition of a film of heavy hydrocarbons on the surface of the tube. It has also been observed by L. Cailletet and later by P. Villard that when allowed to stand in the presence of water at a low temperature a solid hydrate is formed. Acetylene is 17,, Poly, readily decomposed by heat, polymerizing under its meduuou influence to form an enormous number of organic °' compounds; indeed the gas, which can itself be directly '“tyhne' prepared from its constituents, carbon and hydrogen, under the influence of the electric arc, can be made the startingpoint for the construction of an enormous number of different organic compounds of a complex character. In contact with nascent hydrogen it builds up ethylene; ethylene acted upon by sulphuric acid yields ethyl sulphuric acid; this can again be decomposed in the presence of water to yield alcohol, and it has also been proposed to manufacture sugar from this body. Picric acid can also be obtained from it~by first treating acetylene with sulphuric acid, converting the product into phenol by solution in potash and then treating the phenol with fuming nitric acid.

Acetylene is one of those bodies the formation of which is attended with the disappearance of heat, and it is for this reason En“, termed an “endothermic ” compound, in contradisthermlc tinction to those bodies which evolve heat in their "1""? of formation, and which are called “ exothermic.” Such 'my'em'" endothermic bodies are nearly always found to show considerable violence in their decomposition, as the heat of formation stored up within them is then liberated as sensible heat, and it is undoubtedly this property of acetylene gas which leads to its easy detonation by either heat or a shock from an explosion of fulminating mercury when in contact with it under pressure. The observation that acetylene can be resolved into its constituents by detonation is due to Berthelot, who started an explosive wave in it by firing a charge of 0-! gram of mercury fulminate. It has since been shown, however, that unless the gas is at a pressure of more than two atmospheres this wave soon dies out, and the decomposition is only propagated a few inches from the detonator. Heated in contact with air to a temperature of 480° C., acetylene ignites and burns with a flame, the appearance of which varies with the way in which it is brought in contact with the air. With the gas in excess a heavy lurid flame emitting dense volumes of smoke results, whilst if it be driven out in a sufliciently thin sheet, it burns with a flame of intense brilliancy and almost perfect whiteness, by the light of which colours can be judged as well as they can by daylight. Having its ignition point below that of ordinary gas, it can be ignited by any redhot carbonaceous matter, such as the brightly glowing end of a cigar. For its complete combustion a volume of acetylene needs approximately twelve volumes of air, forming as products of combustion carbon dioxide and water vapour. When, however, the air is present in much smaller ratio the combustion is incomplete, and carbon, carbon monoxide, carbon dioxide, hydrogen and water vapour are produced. This is well shown by taking a cylinder one-half full of acetylene and one-half of air; on applying a light to the mixture a lurid flame runs down the cylinder and a cloud of soot is thrown up, the cylinder also being thickly coated with it, and often containing a ball of carbon. If now, after a few moments’ interval to allow some air to diffuse into the cylinder, a taper again be applied, an explosion takes place, due to a mixture of carbon monoxide and air. It is probable that when a flame is smoking badly, distinct'traces of carbon monoxide are being produced, but when an acetylene flame

burns properly the products are as harmless as those of coal

[graphic]
[blocks in formation]

largely adopted for its preparation in laboratories

were :—first, the decomposition of ethylene bromide by dropping it slowly into a boiling solution of alcoholic potash, and purifying the evolved gas from the volatile bromethylene by washing it through a second flask containing a boiling solution of alcoholic potash, or by passing it over moderately heated soda lime; and, second, the more ordinarily adopted process of passing the products of incomplete combustion from a Bunsen burner, the flame of which had struck back, through an ammoniacal solution of cuprous chloride, when the red copper acetylide was produced. This on being washed and decomposed with hydrochloric acid yielded a stream of acetylene gas. This second method of production has the great drawback that, unless proper precautions are taken to purify the gas obtained from the copper acetylide, it is always contaminated with certain chlorine derivatives of acetylene. Edmund Davy first made acetylene in r836 from a compound produced during the manufacture of potassium from potassium tartrate and charcoal, which under certain conditions yielded a black compound decomposed by water with considerable violence and the evolution of acetylene. This compound was afterwards fully investigated by 1.]. Berzelius, who showed it to be potassium carbide. He also made the corresponding sodium compound and showed that it evolved the same gas, whilst in r862 F. Wohler first made calcium carbide, and found that water decomposed it into lime and acetylene. It was not, however, until 1892 that the almost simultaneous discovery was made by T. L. Willson in America and H. Moissan in France that if lime and carbon be fused together at the temperature of the electric furnace, the lime is reduced to calcium, which unites with the excess of carbon present to form calcium carbide. The cheap production of this material and the easy liberation by its aid of acetylene at once gave the gas a position of commercial importance. In the manufacture of calcium carbide in the electric furnace, lime and anthracite of the “HM”, highest possible degree of purity are employed. A tun ol good working mixture of these materials may be taken “MW” as being 100 parts by weight of lime with 68 parts amid" by weight of carbonaceous material. About 1-8 lb of this is used up for each pound of carbide produced. The two principal processes utilized in making calcium carbide by electrical power are the ingot process and the tapping process. In the former, the anthracite and lime are ground and carefully mixed in the right proportions to suit the chemical actions involved. The arc is struck in a crucible into which the mixture is allowed to flow, partially filling it. An ingot gradually builds up from the bottom of the crucible, the carbon electrode being raised from time to time automatically or by hand to suit the diminution of resistance due to the shortening of the arc by the rising ingot. The crucible is of metal and‘ considerably larger than the ingot, the latter being surrounded by a mass of unreduced material which protects the crucible from the intense heat. When the ingot has been made and the crucible is full, the latter is withdrawn and another substituted. The process is not continuous, but a change of crucibles only takes two or three minutes under the best conditions, and only occurs every ten or fifteen hours. The essence of this process is that the coke and lime are only heated to the point of combination, and are no!

« السابقةمتابعة »