Page:The American Cyclopædia (1879) Volume VI.djvu/579

 EMERY such as had_ previously impaired its qualities and reduced its value. The principal consump- tion of the article is in polishing plate glass, and the increase of this business causes a con- stantly increasing demand for emery. The discovery of new localities is a matter of great importance, the few that are known in other parts of the world furnishing no supply capable of competing with that brought from the head of the Mediterranean. It is said to be found near Petschau in Bohemia, near Yekaterinburg in the Ural, near Miyask in the Ilmen branch of that range, and in Frederick valley, Australia. An extensive vein of emery, exhibiting blue crystals of corundum, was discovered a few years ago at Chester, Mass., by Dr. 0. T. Jackson of Boston. The mineral, which had for some time been mistaken for magnetic iron ore, occurs associated with margarite, diaspore, and chlorotoid, in talcose schist. The " Ame- rican Journal of Science " for September, 1873, contains an article by Dr. J. Lawrence Smith giving an account of the discovery of beds of corundum containing emery in North Carolina, Georgia, and Montana. The beds in North Carolina are very extensive ; the corundum is described as being very beautiful, and is found in masses weighing from 600 to 800 Ibs., "hav- ing large cleavages, and being remarkably free from foreign ingredients," and in such quanti- ties as to admit of its use as a substitute for emery. It occurs in chrysolite or serpentine rocks, belonging to a regular system of dikes lying on the N. W. side of the Blue Ridge, at an average distance from the summit of about 10 m., and which have been traversed for 191 m. Dr. Smith remarks that through all the range the corundum forms a geognostic mark of the chrysolite, as it does of the calcareous rock containing corundum, described by him in Asia Minor, and belongs to the same geologic epoch. For a notice of the Montana mineral, see EMERALD. Emery is prepared for use by crushing the stone under stamps, and sorting the powder into different sizes by appropriate sieves. For the most delicate uses of opticians it is separated in a small way by a system of washing over called by chemists elutriation. After being ground, the powder is thrown into water, or water containing gum arabic, or it may be oil, and allowed to subside for a cer- tain number of seconds or minutes. The pro- cess being systematically conducted, the pow- der is sorted into many sizes, and named ac- cording to the time the fluid is allowed to stand before the substance in suspension is col- lected, as emery of 10 seconds, of 30 seconds, 2 minutes, 30, 60, 80 minutes, &c. Emery is applied to paper, thin cloth, and slips of wood, by dusting the powder upon these articles after they have been coated with thin glue. They are then ready for sale or for use under the name of emery paper, cloth, or sticks. Mixed with paper pulp and fine glass and rolled into sheets, it forms the patent razor-strop paper; and by a variety of other methods EMIGRATION 571 it is prepared for convenient application to its numerous uses of grinding and polishing. EMETICS, medicines used to produce vomit- ing. They may be divided into two classes, specific and irritant. The first class require for their operation absorption into the circulation, and they produce their specific effects whether they are absorbed from the stomach or in- jected directly into the blood. When taken internally their action does not commonly com- mence until after 20 or 30 minutes ; then nau- sea, chilliness, and a feeling of weakness are produced, while the pulse is slow and soft; and as vomiting is induced, these give way to a flushed countenance, a warm skin, and a full pulse. The most important of these are tartar emetic (tartrate of antimony and potash), ipe- cacuanha, and the lately discovered apomor- phia, which is an artificial alkaloid, prepared, as its name indicates, from morphia. Tartar emetic has recently been supposed to produce its effect, like the second class, by an irritant action upon the mucous membrane of the stomach, to which it is either directly applied or by which it is excreted when injected into the blood. Apomorphia, when injected sub- cutaneously, acts with great rapidity and in much smaller dose than when given by the stomach. Lobelia inftata, or Indian tobacco, has been largely used as an emetic by botanic practitioners, but is exceedingly depressing in its effects. Irritant emetics, as sulphate of zinc, copper, mustard, &c., on the other hand, produce vomiting by their direct effect upon the lining membrane of the stomach. Their action is immediate and unpreceded by any nausea or other precursory symptoms. They are used chiefly in cases of narcotic poison- ing, and of accumulation in the bronchial tubes, where from the feebleness of the pa- tient it is desirable to shun the depression preceding the action of ordinary emetics, while full and prompt vomiting is required. Emetics were formerly used extensively in the treat- ment of a large variety of diseases ; but the careful observation of recent times has greatly restricted their employment. They find their most appropriate use in relieving the stomach from an excess of food, or from indigestible food, and from poisons, and occasionally in the treatment of bronchitis and croup. EMIGRATION (Lat. e, from, and migrare, to depart), the act of leaving the country or place where one has resided, in order to reside in another. The terms emigration and emigrant are strictly applicable only with reference to the country from which the migration is made, and the converse terms immigration and immigrant are used when express ref- erence to the country into which it is made is intended; but in the unlimited sense of change of residence, the former are generally employed in connection with either the old 01 the new domicile. Of the earliest migrations by which the fundamental features of European history have been defined, no records remain,