§ 192. =Pentane= (C₅H₁₂).--There are three isomers of pentane; that which is used as an anæsthetic is normal pentane, CH₃-CH₂-CH₂-CH₂-CH₃; its boiling-point is 37-38°. It is one of the constituents of petroleum ether. Under the name of “Pental” it is used in certain hospitals extensively, for instance, at the Kaiser Friederich’s Children’s Hospital, Berlin.[179] It is stated to have no action on the heart. [179] _Zeit. f. Kinderheilk._, Bd. iii.-iv., 1893. One death[180] has been recorded from its use:--A lad, aged 14, was put under pental for the purpose of having two molars painlessly extracted. He was only a minute or two insensible, and 4-5 grms. of pental was the quantity stated to have been inhaled. The boy spat out after the operation, then suddenly fainted and died. The _post-mortem_ showed œdema of the lungs; the right side of the heart was empty. The organs of the body smelled strongly of pental. [180] Dr. Bremme, _Vierteljahrsschr. f. gerichtliche Medicin_, Bd. v., 1893. § 193. =Aldehyde= (Acetaldehyde), C₂H₄O = O // CH₃-C , \ H a fluid obtained by the careful oxidation of alcohol (boiling-point, 20·8°), is in large doses toxic; in smaller, it acts as a narcotic. =Metaldehyde= (C₂H₄O₂)₂, obtained by treating acetaldehyde at a low temperature with hydrochloric acid. It occurs in the form of prisms, which sublime at about 112°; it is also poisonous. § 194. =Paraldehyde= (C₆H₁₂O₃) is a colourless fluid, boiling at 124°; specific gravity ·998 at 15°. By the action of cold it may be obtained in crystals, the melting point of which is 10·5°. It is soluble in eight parts of water at 13°; in warm water it is less soluble; hence, on warming a solution, it becomes turbid. Paraldehyde acts very similarly to chloral; it causes a deep sleep, and (judging by experiments on animals) produces no convulsive movements. VII.--Chloral. § 195. =Chloral Hydrate= (C₂H₃Cl₃O₂) is made by mixing equivalent quantities of anhydrous chloral[181] and water. The purest chloral is in the form of small, granular, sugar-like crystals. When less pure, the crystals are larger. These melt into a clear fluid at from 48° to 49°, and the melted mass solidifies again at 48·9°. Chloral boils at 97·5°; it is not very soluble in cold chloroform, requiring four times its weight. The only substance with which chloral hydrate may well be confused is chloral alcoholate (C₄H₇Cl₃O₂), but chloral alcoholate melts at a lower temperature (45°), and boils at a higher (113·5°); it is easily soluble in cold chloroform, and inflames readily, whereas chloral scarcely burns. [181] Anhydrous chloral (C₂HCl₃O) is an oily liquid, of specific gravity 1·502 at 18°; it boils at 97·7°. It is obtained by the prolonged action of chlorine on absolute alcohol.