Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/837

Rh Z I N Z I N 787 The basic carbonate, ZnC0 3 .a:Zn(OH) 2, where x is variable, is prepared by precipitation of a solution of the sulphate or chloride with carbonate of soda. To obtain a product free of Cl or S0 4 , there must be an excess of alkali and the zinc salt must be poured into the hot solution of the carbonate. The precipitate, even after exhaustive washing with hot water, still contains a trace of alkali ; but from the oxide, prepared from it by ignition, the alkali can be washed away. The basic carbonate is, like the oxide, used as a pigment. Normal carbonate of zinc, ZnC0 3, has never been pre pared artificially, but it exists in nature as zinc spar. The sulphate, ZnS0 4 + 7H.,0, white vitriol, is prepared by dis solving the ordinary metal in dilute sulphuric acid. If care be taken to keep the zinc in excess, the solution will be free from all foreign metals except iron and perhaps manganese. Both are easily removed by passing chlorine through the cold solution, to produce ferric and manganic salt, and then digesting the liquid with a washed precipitate of basic carbonate, produced from a small portion of the solution by means of carbonate of soda. The iron and man ganese are precipitated as hydrated sesquioxides, and are filtered off. The filtrate is acidified with a little sulphuric acid and evapor ated to crystallization. The salt crystallizes out on cooling with 7 molecules of water, forming colourless ortho-rhombic prisms, usually small and needle-shaped. They are permanent in the air. According to Foggiale, 100 parts of water dissolve respectively of (7H..O) salt 115-2, 138-2, 161-5, 263 8, 442 6, and 653 6 parts at 0, 10, 20, 50, 80, and 100 C. At 100 C. the crystals lose 6 of their 7 H 2 s ; the rest of the water goes off only at a higher temperature, which lies close to that at which the salt begins to decompose. The anhydrous salt, when exjxjsed to a red heat, breaks up into oxide, sulphur dioxide, and oxygen. An impure form of the salt is prepared by roasting zinc- blende at a low temperature. Sulphate of zinc is used in medicine, chiefly externally. In the arts it is employed in the preparation of varnishes, and as a mordant for the production of colours on calico. A green pigment known as Rinmann s green is prepared by mixing 100 parts of zinc vitriol with 2 5 parts of nitrate of cobalt and heat ing the mixture to redness, to produce a compound of the two oxides. Sulphate of zinc, like sulphate of magnesia, unites with the sulphates of the potassium metals and of ammonium into crystalline double salts, ZnS0 4 .R 2 S0 4 + 6H 2 0, isomorphous with one another and the magnesium salts. The chloride, ZnCl 2, is produced by heating the metal in dry chlorine gas, when it distils over as a white translucent mass, easily fusible, and boiling sufficiently low to be distillable from out of a retort of hard Bohemian glass. Its vapour-density at 900 C. is 4 57, air=l, corresponding to ZnCl 2 (V. and C. Meyer). Chloride of zinc is extremely hygroscopic ; it dissolves in a fraction of its weight of even cold water, forming a syrupy solution. A solution of chloride of zinc is easily produced from metal and hydrochloric acid, but it cannot be evaporated to dryness without considerable de composition of the hydrated salt into oxy-chloride and hydrochloric acid. A concentrated solution of chloride of zinc converts starch, cellulose, and a great many other organic bodies into soluble com pounds ; hence the application of the fused salt as a caustic in surgery, and the impossibility of filtering a strong ZnCl u ley through paper. At a boiling heat chloride of zinc dissolves in any propor tion of water, and highly concentrated solutions, of course, boil at high temperatures ; hence they afford a convenient medium for the maintenance of high temperatures. Oxide of zinc unites with the chloride in a great number of pro portions, forming oxy-chlorides. A (mixed) compound of this order is used as a cement for stuffing teeth and other purposes. One part of extremely fine glass powder is mixed with three of finely powdered oxide of zinc free from carbonic acid. On the other hand, one part of borax is dissolved in the least sufficiency of hot water and added to fifty parts of solution of chloride of zinc of T5 to 1 6 sp. gr. Immediately before use the powder is made into a paste with the solution ; it hardens in a few minutes, forming a stone- like mass. For other zinc compounds, the reader is referred to the handbooks of chemistry. Analysis. From neutral solutions of its salts zinc is precipitated by sulphuretted hydrogen as sulphide, ZnS, a white precipitate, soluble, but by no means readily, in dilute mineral acids, but in soluble in acetic acid. In the case of acetate the precipitation is quite complete ; from a sulphate or chloride solution the greater part of the metal goes into the precipitate ; in the presence of a sufficiency of free HC1 the metal remains dissolved ; sulphide of ammonium precipitates the metal completely, even in the presence of ammonia salts and free ammonia. The precipitate, when roasted at the end of an asbestos stick over a &quot;bunsen,&quot; passes into oxide, which is yellow in the heat and white after cooling ; and, if it be moistened with cobalt solution and re-heated, it exhibits a green colour after cooling. By these tests the precipitate is easily identi fied with certainty. For further information, see handbooks of analysis. (W. I). ) ZINCKEN, or ZINKEN, the German name of a family of wind instruments now obsolete, known in Italy as cornetti, in France as cornets a bouquin, and in England as &quot; cornets.&quot; but differing entirely from the modern cornet sci pistons; these last will also be noticed here, as bearing the same name. The old cornets were of two kinds, the straight and the curved. The straight (Germ, gerade Zincken, stille Zincken ; Ital. cornetti diritti, cornetti muti) were usually made with the mouthpiece (a cupped mouthpiece analogous to that of the trumpet) forming part of the tube. The curved (Germ, krumme Zincken ; Ital. cornetti curvi) are formed of two pieces of wood of different lengths, each having half the channel in which the column of air is to vibrate hol lowed out, the diameter increasing from the mouthpiece towards the lower end. The two pieces of wood, when thus prepared, are joined together with glue ; they are then finished off so as to form a pipe with eight sides, and are finally covered with leather. The mouthpieces are made of wood, horn, or ivory, and are fixed by a tenon to the upper extremity of the pipe. The primitive instru ment was an animal s horn. Pipes of such small length give only, besides the first or fundamental, the second and sometimes the third note of the harmonic series. Thus, a pipe that has for its fundamental note A will, if the pressure of the lips be steadily in- - ; ^ creased, give the octave A and the IpEEErEEiiEE: twelfth E. To connect diatonically the * -^ a 3 first and second, the length of the pipe was progressively shortened, by making holes in its substance for the fingers to cover. The opening of these holes successively furnished the instrumentalist with the different intervals of the scale, six holes sufficing H=r= for this purpose : J^^E^n:rj^ The fundamental ^ ^ &quot; was thus connected with its octave by all the degrees of a diatonic scale which could become chromatic by the help of cross fingerings and greater or less pressure of the lips within the mouthpiece. The fingering r j. ^ was completed by a seventh hole, which had l&EEE^EE for its object the production of the octave without the necessity of closing all the holes in order to produce the second note of the harmonic series. The first complete octave, thus obtained by a succession of funda mental notes, is easily octaved by a stronger pressure of the lips against the mouthpiece, and thus the ordinary limits of the compass of a zincke or cornet extend to a fifteenth. Whether straight or curved, it is pierced laterally with seven holes, six through the front and the seventh, that nearest to the mouthpiece, through the back. The first three holes were usually covered with the third, second, and first fingers of the right hand, the next four with the third, second, and first fingers and the thumb of the left hand. But some instrumentalists inverted the position of the hands. Virdung l shows a kind of zincke made of an animal s horn with only four holes, three at the back of the pipe and one in front. Such an instrument as this had naturally a very limited compass, since with the help of these four holes only the intermediate notes between the second and third proper tones of the harmonic scale could be produced, the lower octave comprised between the first and second remaining incomplete. At the be ginning of the 17th century Prsetorius 2 represents the zincken as a complete family arranged thus : (1) the little zincke, of which the lowest note was that shown in (i.); (2) the ordinary zincke, - -# - ggpz with lowest note (ii.); and KJE=3= fr^ (.3) the cornon, corno torto, * (i.) *&quot; (ii-)&quot;* 1 &quot; (&quot;) 1 Mnsica yetti.tscht und aiiszgezoyen, Basel, 1511. 2 Syntagmatis JIusici, vol. ii. ; Ue Oryanogmphta, &quot;Volfeubuttel, 1618.