An Illustrated Glossary of Technical Terms used in Architectural and Interior Decoration. (Continued from paye 185.) CARTRIDGE PAPER, a thick description of paper of various colours, employed for crayon drawings, cartoons, &c. CHALK, White, a very common species of calcareous earth, of an opaque white colour, and used, when burned into lime, as the basis of cements. Refined by a peculiar process, it is used in the arts to heighten the lights in drawing on coloured and tinted papers. Black Chalk, also called "drawing slate," is of a greyish or bluish-black colour, is massive, and when broken, the principal fracture appears glimmering and slaty, and the cross fracture dull and fine earthy. It stains paper blackthe streak glistening, and of the same colour as the surface. It is easily cut and broken. Red Chalk is a clay coloured by the oxide of iron, of which, according to Rinman, it contains from sixteen to eighteen parts in the hundred. COLOGNE EARTH, a colour of a deep brownish tinge. It contains more vegetable than mineral matter, and originates from the remains of wood long buried in the earth. COMPARTMENT CEILING, a ceiling divided 2. Multiply continually together the two = half sum of two circumf. diameters A B, C D, and the number 11. Divide 16 half diff. of the two diam. 175.92904 16 2814.86464 sq. in. = area. Example 2.-The diameter A c is 30 inches, and the breadth of the ring A E 24 inches: determine its area. 30 the last product by 14, and the quotient will be the area nearly true. Example. What will be the area of the ellipse A D B C A, its transverse A B being 15 feet, and its conjugate C D 10 feet? D B .7854 30 900 900 706.8600 area of circle A B C D A. с should be a homogeneous mass, and possess a uniform capacity for the reception and retention of the magnetic virtue. Metalurgists know that lead melts at a low temperature, but if left on a good fire, it gets first a red, and then a white heat; that, continuing to absorb caloric, it ultimately boils at a uniform heat, which melts gold or silver, as is evident in the process of "6 cupelation." Now here we have a specific heat at probably 5,000 degrees, and we have also a specific heat of boiling water at 212 degrees. It therefore struck me, that by heating my needles in boiling lead, and cooling them in boiling water, every particle of the steel would be first raised to, and then cooled down to the same temperature and degree of hardness. The experiments have been made with complete success; and more powerful magnets have been made in this way than were ever made before, without risk of failure. Magnets weighing 600 grains, and six inches in length, have held in suspension fourteen times their own weight; and compass-needles have given by deflection 30 degrees, at twice their length, from a test-needle. I find that megnets tempered in this way are not liable to break, but possess with great hardness a toughness, derived probably from the boiling water. Their power of retaining the magnetic energy has for four years remained unimpared, although left without "keepers." To manufacturers of magnets and makers of New Mode of making Artificial compass-needles, a knowledge of this mode of Magnets. MAKERS of magnets and compass-needles know that if the most careful and skilful workmen be employed in preparing a number of magnets from the same steel bar, the magnetic power of the magnets, when compared with each other, will greatly vary; although every possible care may be taken in forging, tempering, and magnetising, in an uniform way. Experience in these matters convinced me that discrepancies in the 'magnetic powers of magnets of the same length, weight, and quality of steel, arise from the tempering alone; for if the metal be heated in a furnace, or coal fire, one part of the bar may be in contact with glowing coal, another part in flame, a third in heated air, a fourth in contact with coal in a state of ignition, &c.; consequently, the metal is not in all its parts raised to the same temperature, when suddenly removed from the fire and plunged into a cooling fluid. The relation between the degrees of heat in the heating and cooling mediums is absolutely unknown; magnets tempered in this uncertain way will possess different degrees of hardness throughout their length, and their capacity for magnetism in all their particles will be unequal and uncertain. Reasoning in this way, it appeared to me, that in order to make compass-needles and steel magnets successfully, we require specific heats in the warming as well as in the cooling process of tempering, in order to insure the same degree of hardness throughout the steel bars; that is to say, that the metal when cold tempering steel, at a specific temperature of the heating and cooling mediums, will enable them to make articles of a superior quality without risk of failure, or needless expense. In heating the steel, the bars require to be pressed under the surface of the boiling lead (as the steel would otherwise float on its surface), and the magnet should be suddenly shifted from the lead to the boiling water, the instant it has acquired the temperature of the boiling lead; for to leave it longer in the lead would spoil the smooth surface of the steel, and render it as rough as if heated in a furnace or common fire.-William Walker, in Mechanics' Magazine. DISCOVERY OF PLATINUM IN FRANCE.-M. Gueynard has just informed the General Council of the Isere that he has discovered a the valley of the Drac, which he hopes to vein of platinum in the metamorphic district of work with advantage. Hitherto this precious hardness the lustre of gold and silver, has only metal, which combines with incomparable been met with in the Ural Mountains, and its scarcity has always rendered the price very exhorbitant.-Paris Paper. TO MAKE ARTIFICIAL MINERALOGICAL SPARS. -Saturate water, kept boiling, with alum; then set the solution in a cool place, suspending in it by a hair or fine silk thread, a cinder, a sprig of a plant, or any other trifle;-as the solution cools, a beautiful crystallisation of the salt takes place upon the cinder, &c., which will resemble specimens of mineralogical spar. Sculpture. (Continued from page 171.) THE Greeks originally made use of unhewn stones to represent their divinities. The first improvement was to cut these stones into square blocks. In the course of time, the square block was surmounted by the head of the deity it represented. It is probable that the first statues of this improved nature were those of Hermes or Mercury, from whom they received their name; but the term was applied generally, even though the busts of other divinities or persons of either sex surmounted the pedestal. successful combat, standing before a palladium of the simplest kind. HERMES. Modelling seems at an early period to have engaged the attention of the artificers; clay was used, it was baked when moulded into the form required, and acquired the hardness of stone; baked clay was also used as a mould to receive softer substances which required shape and form, and hence the immense variety of domestic articles in what is called terra cotta, or burnt earth, which are to be seen in every collection of antiquities. The lamps, the vases, the domestic utensils, tiles, ornaments of various descriptions, which are found so constantly in different parts of Italy, are to be referred to the earliest stage of the arts. At Pompeii were found two statues of Jupiter and Juno, above six feet high, of terra cotta, which are now deposited in the Museo Borbbonico at Naples, and two others still better executed but of a similar size. The terra cottas were doubtlessly occasionally painted, for traces are to be found in examination of some of those which are preserved. Stucco or plaster was likewise employed, and many instances remain, some of them also coloured, red being usually adopted. The following drawing of a lamp formed of clay is copied from Passeri's "Lucern. Fictil.," t. ii., f. 99. It represents a youth who has received an amphora, as the prize for some Wax was again another medium of convey-" ing likenesses, or of forming images, the Romans used it generally for busts, and adorned their walls with representations of their friends" formed of this material. Pliny mentions such figures, and upon festive occasions they were adorned with drapery. When marble began to be employed, the finest quarries were ransacked, the texture, the colour, and the granulations of the various excavations became a have descended to us through a long series of source of great attention, and the works that years have been distinguished for the compact texture, and beautiful hue of the marble. In the rials were sought for, aromatics, gums, and at days of the luxury of Rome, fantastic matefuneral ceremonies, those of a combustible nature were used. There existed a statue of Augustus formed of amber; sometimes into busts or statues were inserted foreign substances, either metal, glass, or precious stones for eyes, and various were the attempts made to produce tints and shades. The study of the remaining monuments of antiquity has been the occupation of all the greatest artists who have lived; and the revival of sculpture in Italy must be dated to the period when the minds of the men were awakened to the beauties and excellence that exist of Grecian art, when they availed themselves of them, without servilely copying them, or confining themselves to imitation. (To be continued.) FRENCH POLISH.-Shellac 3 ounces, gum mastich 1 ounce, sandarach 1 ounce, spirits of wine 40 ounces, dissolve in a gentle heat, making up the loss by evaporation. |