In the above representation, the large star towards the left points out the place occupied by the new star among those of Cassiopeia. A new star appeared also in the beginning of the seventeenth century, near the heel of the right foot of Serpentarius. Astronomers agreed that it was perfectly round, resembling one of the fixed stars, and both in vividness and lustre exceeding even the one mentioned by Tycho Brahe; being at one time yellow, at another orange, then red or purple, but most commonly it was of the purest white, when slightly elevated above the horizon. Gradually, at length, its transient light began to fade, and those who watched its waning hue from week to week report, that about a year and one month elapsed from the period of its sudden and brilliant appearance, to its being no longer visible. None of these transient visitors have ever reappeared, and the places which they occupied still remain a blank. A strange mystery seems to hang over such wonderful phenomena-none have solved it, or satisfactorily accounted for appearances of such engrossing interest. The Sun passes from the sign Taurus to Gemini (the Twins) on the 21st of this month, at 5h. 10m. P.M. The Moon is in the constellation Aries till the 2nd, when she enters Taurus; on the 5th, Gemini receives her; on the 6th, Cancer; on the 8th, Leo; on the 10th, Virgo; on the 13th, Libra; on the 15th, Scorpio; on the 16th, Ophiuchus; on the 17th, Sagittarius; on the 20th, Capricornus; on the 22nd, Aquarius; on the 24th, Pisces; on the 27th, Cetus; on the 28th, Aries; on the 29th, Taurus; and on the 31st, Orion. Venus is in the constellation Pisces till the 24th; and in Aries from the 25th to the end of the month. This beautiful planet is a morning star, rising on the first day at 3h. 35m. A.M., and on the last day at 2h. 42. A.M. Mars is in the constellation Pisces till the 30th, and in Cetus on the 31st. He may be seen as a morning star, near the east, at the beginning of the month, and east by north on the 22nd; rising on the 6th at 3h. 19m. A.M., on the 30th at 2h. 16m. A.M. Jupiter is in the constellation Virgo throughout the month. He is visible during the greater portion of the night, and sets on the first day at 4h. 1m. A.M., on the last day at 2h. Om. A.M., between the W. and S. by W. points of the horizon. Saturn may be seen in the constellation Cetus during May. He is visible some short time before sunrise; rising on the first day at 4h. 17m. A.M., on the last day at 2h. 26m. A.M., near the W. by N. point of the horizon. Uranus occupies a place in the constellation Aries. He rises on the 6th at 2h. 25m. A.M.; on the last day, at 2h. 20m. A.M. Neptune rises on the 1st at 2h. 53m. A.M.; on the 15th, at 1h. 59m. A.M. New Moon....................... 1d. 9h. 2m. A.M. 8d. 1h. 34m. F.M. 15d. 8h. 5m. A.M. 23d. 1h. 5m. A.M. 30d. Sh. 47m. P. M. 1ld. 7h. A.M. 23d. 11h. A.M. DOUBLE STARS. Andromeda (Fig. 1) presents a double star لا * + ALMAACK SETA ++ general law of optics, which provides that when the retina of the eye is excited by any bright-coloured light, feebler lights, which if seen alone would look nearly white, appear for the time as if coloured with the tint complimentary to that of the brighter. Thus, for instance, if a yellow colour predominates in the light of the most conspicuous star, that of its attendant in the same field of vision assumes a blueish tinge; whilst, if the tint of the first verges to crimson, that of the second exhibits a tendency to green, or even becomes a vivid green under favourable in her left foot, called Almaack; the small Fig. 3. This figure represents the Polestar; its attendant is very faint, and requires an accurate telescope of considerable power; the Pole-star itself is white, the secondary of a ruddy hue, and is distant 17", or about three or four of its diameters. A beautiful star of this description pertains to the Great Bear; it is called by astronomers Zeta, or Mizar, and may be noticed about the middle of the tail. other, marked , is in the right foot of the same constellation; in this, the two component stars revolve around each other in about sixty years-consequently, nearly a whole circuit has been performed since its discovery at the latter end of the last century. The lesser completes its revolution in fifty-eight years, and is therefore conjectured to move at the rate of two millions four hundred and seventy-one thousand miles every hour, exceeding, by eighty-five times, the velocity of Mercury, the swiftest moving planet of our system. The former contrast is beautifully exhibited by Iota Cancri, the latter by Gamma Andromadæ, both of which are fine double stars. Should, however, the coloured star be less bright than its companion, the other will not be materially affected. Were it possible to look down from some unimaginable height on those sparkling luminaries which shine far above our heads, with visual organs adapted to such a comprehensive view, what glories would be revealed! for not even a bed of tulips affords more exquisite diversity of colour than the stars of which we speak. Two luminaries, a red and green, or blue and yellow, might be seen revolving round a common centre, presenting grateful vicissitudes of day and An-night; in which a beauteous tinge of red or green alternates with light or darkness, as one or other of the varied orbs ascends above the horizon, or sinks below it. Insulated stars of a red colour, nearly resembling that of the Lobelia fulgens, would appear at intervals, but never a decidedly green nor blue star unassociated with a companion brighter than itself. One planetary hemisphere might appear illuminated with a yellow sun, while the other was shone upon with emerald rays; nay more, both suns might occasionally adorn the heavens, shedding their blended hues and contrasted colours over a wide surface. According to the courses of the planets around their central point, would such effects be variously modified, and become productive of almost perpetual variety. A dazzling red luminary might rise above the horizon, while another of the softest emerald green was about to set; and when both were absent, innumerable stars would glit ter in the immensity of space. Another and most interesting subject for contemplation is the contrast afforded by the double stars in point of colour. According to the minute observations of Sir James Herschel, a considerable number exhibit the beautiful and curious phenomena of contrasted hues. When this occurs, the larger star is usually of a ruddy or orange tint, while the smaller is either blue, or green, probably in virtue of that FAMILIAR LECTURES ON CHEMISTRY. LECTURE IX.-CHEMICAL EQUIVALENTSLAW OF MULTIPLES-NOMENCLATURE AND SYMBOLS. BEFORE proceeding further with the study of the individual elements, it will be proper to explain one or two important laws of chemical action, of which the facts already brought before you will afford sufficient illustration. When zinc decomposes hydrochloric acid, one part of hydrogen goes out, and 32.5 parts of zinc take its place; the same is the case when zinc decomposes sulphuric acid. For this reason, the 32.5 parts of zinc are said to be equivalent to the one part of hydrogen. Similarly, bromine decomposes hydriodic acid and metallic iodides, 80 parts of bromine taking the place of 126 parts of iodine; and chlorine decomposes metallic bromides and iodides, 35.5 parts of chlorine taking the place of 80 parts of bromine, or 126 parts of iodine. Hence, the 35.5 parts of chlorine, 80 of bromine, and 126 of iodine, are also said to be equivalent to each other. Again, chlorine decomposes red oxide of mercury, 35.5 parts of chlorine taking the place of 8 parts of oxygen; and accordingly, the 35.5 chlorine are equivalent to the oxygen. Generally: equivalent quantities of any two substances are such as can be substituted for one another in combination. Now, just as in comparing the specific gravities of bodies, we take one substance as a standard, calling its specific gravity 1, and referring all others to it-so likewise, in comparing together the equivalent quantities of different elements, we assume one substance as the unit of the scale, and express the equivalents of all other elements in numbers referred to that unit. Thus, if we take hydrogen as the base of our scale, and call its equivalent 1, we have for the equivalents of other elements: Oxygen 8, Carbon=6, Nitrogen 14, Sulphur 16, Phosphorus 32, Iron = 28, &c. 8 = Hydrogen is usually taken as the unit of the scale, first, because its equivalent is lower than that of any other element-that is to say, when any other substance takes the place of hydrogen in combination, the quantity of that substance which so enters is greater than that of the hydrogen which it displaces; and secondly, because the equivalents of many important elements, as may be seen from the above list, are exact multiples of that of hydrogen, so that when the latter is assumed as the unit, those of the elements in question are expressed by whole numbers. It is not, however, absolutely necessary to take hydrogen as the unit; in many works on chemistry, especially those of continental writers, you will find the equivalent numbers constructed on a scale in which that of oxygen is made equal to 100. Now since the equivalents of different elements must evidently bear the same proportion to each other, whatever substance may be taken for the base of the scale, and since the equivalent of oxygen is 8 on the one scale, and 100 on the other, it follows that the numbers of the former scale may be converted into those of the latter by multiplying by 100 and dividing by 8; thusHydrogen Oxygen Nitrogen Chlorine Carbon Silver 1 8 Oxygen Hydrogen 100 ...... 12.5 6 Carbon 75 Generally, however, the hydrogen scale is preferred, because it gives the simplest numbers. I have hitherto represented the equivalent numbers as determined by the substitution of one element for another. You must not, however, suppose that the actual determination is necessarily made in this manner. Chemical compounds are not always formed by direct substitution; and consequently, the equivalents of elements must often be determined, by comparing the composition of different compounds which exhibit certain resemblances to each other, in their properties or in the mode of their formation. Thus, when hydrogen is heated to a certain temperature in contact with oxygen, 1 part of hydrogen unites with 8 parts of oxygen to form water. Similarly, when copper is heated to redness in the air, 32 parts of the metal take up 8 parts of oxygen, to form the black oxide of copper. Here we see that 32 parts of copper perform the same function as 1 part of hydrogen; that is to say, they combine with 8 parts of oxygen: accordingly we say, that the equivalent of copper is 32. Again, mer You may see, by combine with a given quantity of the other, are all multiples of the lowest; thus, in the last example, the quantities 16, 24, 32, and 40 are exact multiples of 8-that is to say, they may be divided by 8 without a remainder. Hence, the law which expresses this fact is called the Law of Multiples. It is necessary to observe, however, that this cury forms two compounds with oxygen, viz., the black oxide, containing 200 parts of mercury and 8 of oxygen; and the red oxide, containing 100 of mercury and 8 of oxygen. Now, of these, the red oxide bears a much closer analogy, in its chemical properties, to the oxide of copper just mentioned, than the black oxide does. We therefore conclude, that 100 parts of mer-law is not universal; for intermediate procury correspond, in chemical power, to portions are often met with. Thus, carbon 32 parts of copper, and accordingly, we and oxygen form three compounds, viz.— fix the equivalent number of mercury at carbonic oxide, containing 6 parts of carbon 100. Generally-but not invariably-when and 8 of oxygen; oxalic acid, composed of a substance forms several compounds with 6 carbon and 12 oxygen; and carbonic acid, oxygen, the largest quantity of that sub-containing 6 carbon and 16 oxygen. Now stance which can combine with 8 parts of these quantities of oxygen are in the prooxygen, is taken as the equivalent. Thus, portion of 1, 1, and 2. Again, lead forms nitrogen and oxygen form five compounds, four oxides, in which 104 parts of lead in which parts of oxygen are severally are combined with 8, 103, 12, and 16 parts united with 14, 7, 4, 3, and 23 parts of of oxygen, quantities which are to one nitrogen; and accordingly, 14 is taken as another as the numbers 1, 13, 11, and 2. the equivalent of nitrogen. Chemical Nomenclature.-The law of comLaw of Multiples. bination just explained is made the foundseveral examples, both in this and the pre-ation of a system of nomenclature, in which ceding lectures, that when two substances the name of a substance serves as an index form a series of compounds, the quantities of the proportion in which its elements are of the one substance which unite with a combined. This system will be most congiven quantity of the other, bear a very veniently explained by referring to the simple relation to each other. Thus, hy- compounds of metals with oxygen, chlorine, drogen and oxygen form two compounds, iodine, &c. You are aware that these comviz. water, composed of 1 part hydrogen pounds are called oxides, chlorides, iodides, and 8 oxygen; and peroxide of hydrogen &c. Now, a compound of 1 equivalent of a containing 1 part hydrogen with 16 parts metal with 1 equivalent of the other element, oxygen. Here the quantities of oxygen is denoted by the prefix proto, meaning first; which unite with the same quantity of hy- whence are formed the terms protoxide, drogen, are to one another as 1 to 2. The protochloride, &c. Compounds containing two oxides of mercury above mentioned 1 equivalent of a metal united with 1§, 2, 3, furnish another example precisely similar. 4, and 5 equivalents of the other element, Look again at the compounds of chlorine are distinguished by the prefixes sesqui, bi, and oxygen. In that series, 35.5 parts of ter, quadro, and quinto; so that we have chlorine are combined with 8, 24, 32, 40, the terms sesqui-oxide, bi-oxide or bin-oxide, and 56 parts of oxygen, quantities which ter-oxide, quadro-chloride, quinto-bromide, are to one another as the numbers 1, 3, 4, &c. For example, tin forms two oxides, 5, and 7; in other words, these compounds viz., the protoxide, containing 59 parts are formed of 1 equivalent of chlorine com- (1 eq.) of tin united with 8 parts (1 eq.) of bined respectively with 1, 3, 4, 5, and 7 oxygen; and the bi-oxide, containing 59 equivalents of oxygen. As another example, parts of tin with 16 parts (2 eq.) of oxygen. take the compounds of oxygen and nitro- Similarly, we have the protoxide of iron, gen above mentioned. In this series of containing 28 parts (1 eq.) of iron with 8 compounds 14 parts of nitrogen are com- parts (1 eq.) of oxygen; and the sesquibined with 8, 16, 24, 32, and 40 parts of oxide, containing 28 parts of iron with 12 oxygen, or 1 equivalent of nitrogen with 1, parts (14 eq.) of oxygen. Antimony forms 2, 3, 4, and 5 equivalents of oxygen. Now, two compounds with chlorine, viz. the terin all these examples, you may observe that chloride, containing 129 parts (1 eq.) of the several quantities of the one substance antimony with 106-5 parts (3 eq.) of chlo (oxygen, in the examples chosen), which rine; and the quinto-chloride, composed of 129 parts of antimony with 1755 parts (5 eq.) of chlorine. Sometimes, though less frequently, we meet with compounds containing 2 or 3 equivalents of a metal united with 1 equivalent of oxygen, chlorine, &c. Such compounds are distinguished by the Greek prefixes di and tris. Thus, the black oxide of mercury, which contains 200 parts (2 eq.) of the metal with 8 parts (1 eq.) of oxygen, is called the di-oxide of mercury. The preceding are the principal terms requiring explanation in this place: there are a few others also in use, but they will be best explained as they occur. It may be as well, however, to mention the term peroxide, sometimes used to denote the highest degree of oxidation of a substance, not accompanied by the production of acid properties. Thus, among the oxides of manganese, the common black oxide, composed of 1 eq. of manganese with 2 eq. of oxygen (which should, therefore, according to the system just explained, be called a bi-oxide), is generally called the peroxide of manganese, because it is the highest oxide of that metal not possessing acid properties. This term, peroxide, you must observe, has no reference to the proportions in which the metal and the oxygen are united; it is applied indifferently to the bi-oxide of manganese and the sesqui-oxide of iron. Chemical Symbols. It is very convenient to have some short method of expressing in writing the constitution of chemical compounds. For this purpose, a system has been devised, which consists in representing the equivalent of each element by the initial letter of its name, and the combination of elements by the juxtaposition of these symbols. Thus, hydrogen is represented by H, oxygen by O, and water by HO. Similarly, iodine being denoted by I, and fluorine by F; the symbols H I, and H F, denote hydriodic and hydrofluoric acid respectively. Such is the general principle on which the chemical symbols are constructed. It happens, however, that many of the elementary bodies have names beginning with the same letter. In such cases, the single letter is usually appropriated to one of them, and the others are denoted by that letter joined with some other letter of their names. Thus, carbon is denoted by C, calcium by Ca, cobalt by Co, and chlorine by Cl. Moreover, since the names of the elements in the different languages of Europe do not always begin with the same letter (thus, iron is in French, fer, and in German, eisen); and since it is important that the symbols should be of universal application, and not confined to any one language-it has been agreed to form them from the Latin names of the elements: thus, copper (cuprum) is represented by Cu, iron (ferrum) by Fe, tin (stannum) by Sn, &c. In the majority of cases, however, the Latin and English names possess the same initial letter; it is chiefly in the names of the ordinary metals, such as gold, silver, lead, iron, tin, &c., that differences exist in this respect. You must particularly observe that the chemical symbols denote, not merely the names of the elements, but equivalent quantities of those elements; for instance, H and O invariably refer to quantities of hydrogen and oxygen, which are to one another as 1 to 8. When a compound contains two or more equivalents of any of its elements, the number of those equivalents is denoted by a small figure placed at the right of the symbol, and a little below it: thus, the compounds of chlorine and oxygen, in which I equivalent of chlorine is combined with 1, 3, 4, 5, and 7 equivalents of oxygen, are expressed in symbols as follows: Similarly, the compounds of nitrogen and oxygen, in which 14 parts of nitrogen are combined with 8, 16, 24, 32, and 40 parts of oxygen, are denoted by N O, NO2, N O,, N Ó4, and N 05. The great advantage of these symbols is, that they enable us to represent chemical decompositions in the form of equations. Thus, for the action of zinc on hydrochloric acid, we have: H CI+Zn Zn Cl + H; which means, that hydrochloric acid and zinc, when placed in contact, produce chloride of zinc, and free hydrogen. The |