Chemically, the chlorites are distinguished from the micas by the presence of a considerable amount of water (about 13%) and by not containing alkalis; from the soft, scaly, mineral talc they differ in containing aluminium (about 20%) as an essential constituent. The magnesia (up to 36%) is often in part replaced by ferrous oxide (up to 30%), and the alumina to a lesser extent by ferric oxide; alumina may also be partly replaced by chromic oxide, as in the rose-red varieties kämmererite and kotschubeite. The composition of both clinochlore and penninite is approximately expressed by the formula H8(Mg,Fe)5Al2Si3O18, and the formulae of prochlorite and corundophilite are H40(Mg,Fe)23Al14Si13O90 and H20(Mg,Fe)20Al8Si6O45 respectively. The variation in composition of these orthochlorites is explained by G. Tschermak by assuming them to be isomorphous mixtures of H4Mg3Si2O9 (the serpentine molecule) and H4Mg3Al2SiO9 (which is approximately the composition of the chlorite amesite). The leptochlorites are still more complex, and the intermixture of other fundamental molecules has to be assumed; the species recognized by Dana are daphnite, cronstedtite, thuringite, stilpnomelane, strigovite, diabantite, aphrosiderite, delessite and rumpfite.
The chlorites usually occur as alteration products of other minerals, such as pyroxene, amphibole, biotite, garnet, &c., often occurring as pseudomorphs after these, or as earthy material filling cavities in igneous rocks composed of these minerals. Many altered igneous rocks owe their green colour to the presence of secondary chlorite. Chlorite is also an important constituent of many schistose rocks and phyllites, and of chlorite-schist it is the only essential constituent. Well-crystallized specimens of the species clinochlore are found with crystals of garnet in cavities in chlorite-schist at Achmatovsk near Zlatoust, in the Urals, and at the Ala valley near Turin, Piedmont; also as large plates at West Chester in Pennsylvania and at other American localities. Crystals of penninite are found in serpentine at Zermatt in Switzerland and in the green schists of the Zillerthal in Tirol.
Closely allied to the chlorites is another group of micaceous minerals known as the vermiculites, which have resulted by the alteration of the micas, particularly biotite and phlogopite. The name is from the Latin vermiculor, “to breed worms,” because when heated before the blowpipe these minerals exfoliate into long worm-like threads. They have the same chemical constituents as the chlorites, but the composition is variable and indefinite, varying with that of the original mineral and the extent of its alteration. Several indistinct varieties have been named, the most important of which is jeffersonite.
(L. J. S.)
CHLOROFORM (trichlor-methane), CHCl3, a valuable anaesthetic, a colourless liquid, possessing an agreeable smell and a pleasant taste. It may be prepared by the action of bleaching powder on many carbon compounds, such, for example, as ethyl alcohol and acetone (E. Soubeiran, Ann. chim. phys., 1831 [2], 48, p. 131; J.v. Liebig, Ann., 1832, I, p. 199), by heating chloral with alkalis (Liebig), CCl3CHO + NaHO = CHCl3 + NaHCO2, or by heating trichloracetic acid with ammonia (J. Dumas, Ann., 1839, 32, p. 113). In the preparation of chloroform by the action of bleaching powder on ethyl alcohol it is probable that the alcohol is first oxidized to acetaldehyde, which is subsequently chlorinated and then decomposed. Chloroform solidifies in the cold and then melts at -62° C.; it boils at 61.2° C., and has a specific gravity 1.52637 (0°/4°) (T.E. Thorpe). It is an exceedingly good solvent, especially for fats, alkaloids and iodine. It is not inflammable. The vapour of chloroform when passed through a red-hot tube yields hexachlorbenzene C6Cl6, perchlorethane C2Cl6, and some perchlorethylene C2Cl4 (W. Ramsay and S. Young, Jahresberichte, 1886, p. 628). Chromic acid converts it into phosgene (carbonyl chloride, COCl2). It reacts with sodium ethylate to form ortho-formic ester, CH(OC2H5)3, and when heated with aqueous ammonia for some hours at 200-220° C. gives carbon monoxide and ammonium formate, 2CHCl3 + 7NH3 + 3H2O = NH4·HCO2 + CO + 6NH4Cl (G. André, Jahresb., 1886, p. 627). When digested with phenols and caustic soda it forms oxyaldehydes (K. Reimer, Ber., 1876, 9, p. 423); and when heated with alcoholic potash it is converted into potassium formate, CHCl3 + 4KHO = KHCO2 + 3KCl + 2H2O. It combines with acetoacetic ester to form the aromatic compound meta-oxyuvitic acid, C6H2·CH3·OH·(COOH)2. A hydrate, of composition CHCl3·18H2O, has been described (G. Chancel, Fresenius Zeitschrift f. anal. Chemie, 1886, 25, p. 118); it forms hexagonal crystals which melt at 1.6° C.
Chloroform may be readily detected by the production of an isonitrile when it is heated with alcoholic potash and a primary amine; thus with aniline, phenyl isocyanide (recognized by its nauseating smell) is produced,
CHCl3 + C6H5NH2 + 3KHO = C6H5NC + 3KCl + 3H2O.
For the action and use of chloroform as an anaesthetic, see [Anaesthesia]. Chloroform may be given internally in doses of from one to five drops. The British Pharmacopoeia contains a watery solution—the Aqua Chloroformi—which is useful in disguising the taste of nauseous drugs; a liniment which consists of equal parts of camphor liniment and chloroform, and is a useful counter-irritant; the Spiritus Chloroformi (erroneously known as “chloric ether”), which is a useful anodyne in doses of from five to forty drops; and the Tinctura Chloroformi et Morphinae Composita, which is the equivalent of a proprietary drug called chlorodyne. This tincture contains chloroform, morphine and prussic acid, and must be used with the greatest care.
Externally chloroform is an antiseptic, a local anaesthetic if allowed to evaporate, and a rubefacient, causing the vessels of the skin to dilate, if rubbed in. Its action on the stomach is practically identical with that of alcohol (q.v.), though in very much smaller doses. The uses of chloroform which fall to be mentioned here are:—as a counter-irritant; as a local anaesthetic for toothache due to caries, it being applied on a cotton-wool plug which is inserted into the carious cavity; as an antispasmodic in tetanus and hydrophobia; and as the best and most immediate and effective antidote in cases of strychnine poisoning.