ARENATION-AREOLA. soils. The flowers are generally small and inconspicuous, but, if closely examined, are seen to possess no little beauty. ARENATION, n. ǎr-e-nā'shūn [L. arenatio, from arenare, to sprinkle with sand]: in med., a sand-bath; sprinkling hot sand upon the body ARENDAL, d'ren-dál': town on the s.e. coast of Norway, near the mouth of the Nid-elf in the bay of Christiania. It is built partly on piles, partly on rock, and this with its situation gives it a very romantic aspect. The bay, protected by the island of Tromöe, forms an excellent harbor, and favors the commerce of the town, which is considerable, in proportion to its size. A. is intersected by canals; its exports are iron from the neighboring mines, and wooden articles. Ship-building is carried on; and on a smaller scale, distilleries and tobacco-factories. King Louis Philippe, after the French Revolution, when wandering in the north as Duke of Orleans, made some stay here. Pop. 4,000. ARENDALITE, n. ă-rěn'dal-it. [In Ger., arendalit, from Arendal, near which it is found]: a mineral, a subvariety of ordinary Epidote. It generally occurs in darkgreen crystals. ARENDATOR, n. ăr'en-da'tor [L. L.]: in Livonia and other provinces of Russia, one who farms the rents or revenues; one who contracts with the crown for the rents of the farms. ARENG', or ARENGA. see GOMUTO PALM. ARENI'COLA: see ANNELIDA. ARENICOLITES, n. plu. ăr'ě-nik'õ-līts [L. arēna, sand; colo, I inhabit; Gr. lithos, a stone]: a term used to designate those circular holes or markings which appear on the upper surface of many sandstones, having apparently been worm-burrows. ARENILITIC, a. ă-rěn'ă-lĭt'ik [L. arēna, sand: Gr. lithos, a stone]: of or like sandstone. ARENOSE, a. ǎr'ĕ-nōs, or ARENOUS, a. ăr'ě-nus, sandy. ARENARIOUS, a. ăr'ě na'. ri-us, sandy; composed wholly or in large part of sand. ARENULOUS, 8. ă-rěn'ū-lés, full of sand; gritty. AREOLA, n. ǎ-r'ěõ-lă [L. ărěšla, a small open space, a small garden-bed: F. aréole]: the colored circle round the nipple or a pustule. ARE'OLÆ, n. plu. -lē, small interstices of cellular or other tissues; little spaces on the area or surface. AREOLAR, a. à-re'ŏ-ler, of or like an areola. AREOLATE, a. ǎ-rĕ'ŏ-lāt, marked by areolæ, or little spaces or cavities. ARE'OLA'TION, n. -shun, any small space distinctly bounded by something different in color, texture, etc. AREOLAR TISSUE, the tissue that loosely connects skin with muscle, and also forms a soft connective packing between muscles, around blood-vessels etc., and is composed mainly of interlaced white fibrous' and 'yellow elastic' tissues. AREOMETER. AREOMETER, n. ār'ě-ŏm'ĕ-tėr [Gr. araios, rave, thin; metron, a measure]: an instrument for measuring the specific gravity of liquids. AR'EOM'ETRY, n. -tri. AR'EOMETRICAL, a. -ri-kal, pertaining to. AREOMETER [Fr. aréomètre, or pèse-liqueur: Ger. Aräometer or Senkwage], called also HYDROMETER: an instrument which is allowed to float freely in liquids, to determine their specific gravity or that of solid bodies. By specific gravity (q.v.) is meant the ratio that the weight of any volume of a substance bears to the weight of the same volume of water. Thus, a cubic foot of alcohol weighs 793 oz., while the same quantity of water weighs 1,000 oz.; the specific gravity of alcohol is set down, therefore, as fo or 793. A cubic foot of sulphuric acid weighs 1,841 oz., and has, consequently, a specific gravity of 1841. These relations are not confined to the particular volume, one cubic foot, of these bodies, but hold for any equal volumes of them. Equal volumes of alcohol, water, and sulphuric acid have always to each other the ratio respectively of 793, 1,000, and 1,841; and this is only an instance of the general principle, that equal volumes of different substances have weights bearing to each other the direct ratio 793 of the specific gravities of these substances. This is the principle on which areometers with weights, or weightareometers, are constructed. If, however, equal weights of any two of these liquids were taken, it would be found that .793 of a cubic foot of water would weigh as much as 1.000 cu. ft. of alcohol; 1'000 cu. ft. of sulphuric acid as much as 1.841 cu. ft. of water; or 793 cu. ft. of sulphuric acid as much as 1.841 cu. ft. of alcohol: more generally thuswhen equal weights of two different fluids are taken, the AREOMETER. volumes of each are inversely as their specific gravities. On this latter principle depends the use of areometers with scales, or scale-areometers. The scale-A. is employed much more commonly than the weight-A., and is, in consequence, a much more important instrument. Of the various forms of scale-areometers, that contrived by Gay-Lussac deserves particular notice, from the simplicity of the mode of graduation; and an account of it will give the best idea of the general nature of such instruments. See Fig. 1. It consists of a uniform glass tube, AB, blown into two bulbs, C and D, at the bottom. The lower bulb, D, is loaded with mercury, so that when the instrument floats in any liquid the stem, AB, is maintained in a vertical position. Suppose that the quantity of mercury is so adjusted that when placed in water the A. sinks to the point W, which may in consequence be called the water-point. According to the principle of Archimedes, the weight of the volume of water displaced by the instrument up to this point is equal to the weight of the instrument. Suppose, for the sake of simplicity, that the water so displaced is a cubic inch, the weight of the A. will be that of a cubic inch of water, or 250 grs. (more correctly 252 5 grs. at 60° F.). If the A. be now placed in a fluid heavier than water, such as a mixture of sulphuric acid and water having a specific gravity or 1.25, it is manifest that if it is sunk again to the water-point. the displaced fluid would weigh of 250 = 312 grs., or 624 grs. more than the weight of the instrument. As much, therefore, of the stem of the A. must rise above the liquid as will reduce the weight of the displaced liquid to 250 grs., or reduce the volume to of what it was before. If the stem in this case rises to B, the volume displaced by the part WB is of the volume displaced by the instrument at the water-point. If the whole be divided into 100 parts, and the mark 100 be at W, B must be marked 80, as the A displaces up to that point of 100; and if the intervening space on the stem be divided into 20 equal parts, each of them will correspond with 10 of the water volume-viz., 01 of a cubic inch, or with of the weight of the instrument-viz., 25 grs. If the same scale be carried above the point W., and the divisions marked as ascending from 100, the A. will be serviceable likewise for fluids less dense than water, and will mark the volumes which it displaces in each of them. The A. thus graduated gives immediately the volumes which it displaces in different liquids; and from these, seeing that it displaces in every case a weight of liquid equal to its own, the specific gravities may be calculated according to the principle already stated—viz., that equal weights of two different fluids have volumes inversely as their specific gravities. If, in a mixture of sulphuric acid and water, the A. stands at 90, according to the above principle 90 volumes of the mixture weigh as much as 100 of water; therefore its specific gravity is 100 or 1. Again, if in a mixture of spirits and water it should stand at 110, 110 volumes of the mixture weigh as much as 100 of water, so that its specific gravity is 10%, or 1. In all cases, then, 100 is to be divided by the number read on AREOMETER. the A., to determine the specific gravity of the liquid in which it floats. The delicacy of the A. depends on the distance of the divisions on the scale, or on the thinness of the stem compared with the bulbs. An instrument possessing this advantage cannot be made to serve both for liquids heavier and lighter than water, for the stem would be of an inconvenient length; and it is usual to construct two areometers-one marked with the water-point at the top, and the scale descending to 50, for fluids heavier than water; and the other, with the water-point at the bottom, and the scale ascending to 150, for fluids lighter than water. The scale is generally marked on a slip of paper fixed inside the stem. Gay-Lussac's A. is known also under the name volumenometer.' Although it cannot be surpassed either for accuracy or simplicity, it is much less used than other instruments of a similar nature furnished with arbitrary scales, requiring the aid of tables to interpret the readings. The best known of these is Twaddle's A., used in England; and Beaumé's A., extensively adopted on the continent of Europe. The A. with an equally divided scale is a very ancient instrument; it was known among the Greeks under the name of 'baryllion.' On some areometers the divisions are not at equal distances, but are so drawn as to give at once, without table or calculation, the specific gravity of the fluid in which they are placed. Although very desirable, in practice they do not possess the accuracy of the A. with equally divided scales, because the graduation of them is attended with considerable difficulty. No form of A. can be made to determine specific gravities with perfect accuracy, and such instruments are only useful where a ready and good approximation is all that is needed. They are, in consequence, employed chiefly to ascertain the specific gravity of the various liquors and solutions which occur in the arts and manufactures, and very frequently they are graduated with reference to special liquids, as spirits, wine, milk, brine, etc. The Alcoholometer or Hydrometer of Sykes is an instrument of this latter description, and is used by excise officers for estimating the strength of spirits. It is represented in Fig. 2. BC is a hollow brass ball, surmounted by a flat stem, AB, and loaded below by a short conical stem. CD, terminated by the pear-shaped bulb, D. It is accompanied by eight weights, by which the weight of the instrument may be increased, and the range of the scale extended to fluids heavier as well as lighter than water. One of these weights, W, is shown in the figure; it is furnished with a slit, so as to allow of it being slipped on to the narrowest part, C, of the lower stem. The stem, AB, is graduated into 11 equal parts, and these again into halves; and the instrument is so adjusted that its indications give the volumes of water that must be added to or taken from 100 volumes of the mixture under examination to reduce it to proof spirit (see ALCOHOL), which is a mixture of nearly equal parts of water and alcohol. Thus, if the A. indicates 11 over proof, 11 volumes of water must be added in order to bring the liquid down to proof |