373 



CYANOXALIC ACID. 



CYCLOID. 



374 



tion is that the venous blood passes to the left side of the heart with- 

 out undergoing its proper amount of oxygenation in the lungs. The 

 effect of this abnormal mixture of the two bloods is not to destroy life 

 immediately, but to produce a series of symptoms, the most prominent 

 of which is a blueness of the skin, constituting the disease called 

 cyanosis. This is not an unfrequent occurrence, and according to the 

 extent of the communication between the two sides of the heart will 

 be the intensity of the disease. Sometimes the feebleness and derange- 

 ment of the system causes death within a few hours after birth ; in 

 other cases persons have been known to attain mature age labouring 

 under this affection. 



The effect of this malformation, according to its degree, is to dimi- 

 nish the nutrition of the body, and to produce general weakness and 

 exhaustion. The functions of the heart and lungs are interfered with, 

 and there is frequently a rapid intermitting pulse, with attacks of 

 difficulty of breathing. The bluenesa of the skin is increased during 

 these attacks. There is generally coldness of the skin from the imper- 

 fect nature of the respiratory changes which go on in the body. There 

 is also a tendency to dropsical effusion in various parts of the body. 



In this disease little can be done to effect a cure. The great object 

 is to alleviate any distressing symptoms which may arise. 



CYANOXALIC ACID. [Unic ACID.] 



CYANURENIC ACID, an acid found in the urine of the dog. It 

 much resembles uric acid, but differs in being soMble in hydrochloric 

 acid. It is obtained from the tenacious deposit that forms when the 

 urine of the dog is set aside for some time. That substance is dissolved 

 in lime-water, and sufficient hydrochloric acid added to neutralise the 

 lime ; cyanurenic acid then separates in the form of small colourless 

 needles. It is insoluble in alcohol, is sublimed by heat, and is then 

 soluble in alcohol. It forms salts with bases, some of which are 

 crystalline. 



CYANURIC ACID (3(HO, CyO) + 4Aq., or 8HO, C 6 N 3 3 + 4Aq.). 

 This acid was discovered by Scheele in the distillation of urie acid ; 

 more lately Serullus obtained it by another process, and described it 

 under the name of cyanic acid ; and lastly, Wohler and Liebig examined 

 its constitution and properties. 



This acid is formed under various circumstances, as by the decom- 

 position of solid chloride of cyanogen by water, the decomposition of 

 soluble cyanates by dilute acid, and the distillation of uric acid, &c. 



In order to prepare it, the best process seems to be to dissolve dry 

 melam [MELA.M] with a gentle heat in concentrated sulphuric acid; 

 the solution is to be poured into 20 or 30 parts of water, and the mix- 

 ture is to be kept for several days, at a temperature near ebullition, or 

 until small portions yield no white precipitate with ammonia. The 

 solution is then to be evaporated to its crystallising point, and the 

 crystals obtained are to be purified by recrystallisation. 



Cyanuric acid forms rather small colourless prismatic crystals, which 

 are efflorescent, losing at ordinary temperatures the whole of their 

 water of crystallisation. It is very slightly soluble in cold water, and 

 requires 24 parts of boiling water to dissolve it ; it is inodorous, has 

 but little taste, and reddens litmus but feebly. It is a remarkably 

 permanent substance, being soluble without decomposition in concen- 

 trated sulphuric or nitric acid, though when heated in them it is 

 eventually decomposed. 



According to Liebig, the crystallised acid consists of 3 equivalents of 

 cyanogen 78, 3 equivalents of oxygen 24, 7 equivalents of water 63, 

 equivalent = 165 : 3 equivalents of the water constitute the acid a 

 hydrate, and 4 equivalents are water of crystallisation. It combines 

 with 3 equivalents of base to form cyanurates, and is therefore what is 

 termed a tribasic acid. By exposure to a very high temperature 

 1 equivalent of hydrated cyanuric acid is decomposed into 3 equiva- 

 lents of hydrated cyanic acid. Urea is by heat converted into cyanuric 

 acid and ammonia. 



CYBELE. [RHEA.] 



CYCLAMIN. [ARTHANITIN.] 



CYCLE, which means nothing but circle (m/itAos), has an arbitrary 

 use in chronology. Certain of the cycles, or recurring methods of 

 denoting time, which are in common use, are called cycles, to the 

 exclusion of the rest. The principal of these, if not the only ones, are 

 the Metonic cycle [METON, BIOG. Div. ; CALIPPUH, Bioo. Drv.J, the 

 SOLA.U. cycle, and the cycle of INDICTION. But the natural cycles, such 

 as the revolutions of the sun and moon, are not called cycles; nor 

 even some of the artificial ones, such as the Julian period. It would 

 be useless to retain this artificial and confused distinction. Under the 

 distinctive words METON, Bioo. Div., INDICTION, Ac., the reader will 

 find the origin of each method of reckoning; while in the article 

 PIBIOD OF REVOLUTION, he will see a table of the lengths and com- 

 mencements of all the cycles, natural and artificial, whether called 

 cycle, i>erio<1 , year, day, or month. 



C Y< 'LOd KAPH, or ARCOGRAPH, is an instrument for drawing arcs 

 of circles without centres, and is used in architectural and engineering 

 drawing, when the centres are too distant to be conveniently accessible. 

 One such contrivance, which however does not produce perfectly 

 circular arcs, i.i noticed under COMPASSES. Bricklayers and masons, 

 when they wish to strike an arc for the tops of doors and windows, 

 have recourse to a very simple mode of accomplishing the object, by 

 driving a nail into the wall at each extremity of the intended arc, and 

 then nailing two straight laths or rods together at such an angle that 



while their external sidea or edges are in contact with the nails driven 

 in the wall, their apex or meeting point shall touch the crown of the 

 required arch. A tracing point in the apex will then describe the 

 required arc. The same plan may be adopted in drawing on paper, 

 substituting pins for the nails, and a piece of stout cardboard, cut to 

 the required angle, for the laths. Mr. Rotch's Arcograph, described in 

 the ' Transactions ' of the Society of Arts, vol. xxxix. pp. 49-51, is an 

 instrument consisting of two rules connected together by a joint which 

 forms a socket for a pencil, and furnished with two quadrant-shaped 

 pieces of brass, sliding upon one another, by which the rules may be 

 set to any required angle, and secured by clasps. This instrument ia 

 used in the same way as the laths above described, and it affords the 

 means [of ^measuring, by the graduation of one of the quadrants, the 

 degrees contained in the arcs described by it. Mr. Alderson's Curri- 

 linead, described in the forty-fourth volume of the same work, pp. 

 151-156, is another instrument on the same principle, but of more 

 perfect construction, in which the pencil may be projected beyond 

 the apex of the angle for the purpose of drawing a second arc parallel 

 with the first. This second arc is not mathematically correct, but, 

 when on a small scale, it is sufficiently so for all ordinary purposes. 



The Centrolinead of Mr. Peter Nicholson, described in the thirty- 

 second and thirty-third volumes of the ' Transactions ' of the above 

 Society, pp. 67-70 and 69-81, is an instrument acting on the same 

 principle, although its chief use is, not as a cyclograph, but as an 

 instrument for drawing lines converging to a distant and inaccessible 

 point. It may be compared to a T-rule in which the transom consists 

 of two pieces adjustable to any required angle with each other, and 

 the centre of which, answering to the apex of the cyclographs above 

 described, is precisely on a line with the fiducial or drawing edge of 

 the stem or long limb of the rule. The instrument being once 

 adjusted to the required angles, and having its angular transom laid 

 against two fixed pins, just like the angle of a cyclograph, any number 

 of converging lines may be drawn by it as readily as parallel lines 

 drawn by a common T-rule, with its transom sliding against the edge 

 of the drawing-board. 



Another instrument rewarded by the Society of Arts, and described 

 in the thirty-fifth volume of their ' Transactions,' pp. 109-112, under 

 the name of a Curvoyraph, was contrived by Mr. Warcup for copying 

 or transferring curved lines, or describing them originally, of any 

 required curvature, by means similar to those adopted in the instru- 

 ment represented under BEVEL. The adjustable ruler itself consists 

 of a thin pliable slip of whalebone, and the adjusting ribs, answering 

 to the screws ff, in the figure above referred to, instead of being 

 screwed, are merely secured in any required position by the pressure 

 of wedges acting upon small pieces of cork inserted in the ruler or 

 stock through which they pass. 



CYCLOID (KVK\ofi$-fis, like a circle), a name very incorrectly given 

 to the curve which is traced out by any point of a circle rolling on a 

 straight line. Thus while the wheel of a carriage revolves, each nail 

 on the circumference describes a succession of cycloids ; more cor- 

 rectly, a succession of branches of one cycloid. We might also here 

 describe the various curves made by the points of circles which roll 

 inside or outside of other circles, &c. &c. But as the cycloid stands 

 apart from all the rest, both in simplicity and historical notoriety, we 

 shall here confine ourselves to this one curve alone, and refer the rest 

 to the head TBOCHOIDAL CORVES. 



If we suppose a circle to roll on a straight line, it is obvious that 

 the centre will advance in every moment through a length equal to 

 the portion of the circumference which is brought in contact with the 

 line on which the circle rolls. That is, 



supposing c, the point now highest on the circle, to bo the one whose 

 path is to be traced, then, by the time the mere rotation would have 

 brought this point to p, the whole system will have been carried 

 forward through a length p Q equal to the arc c P. Hence follows a 

 very simple mode of conceiving the form of a cycloid : at every point 

 r imagine a line p Q parallel to A B and equal to the arc c r ; the extre- 

 mities of all these lines will be in the cycloid. The arc A c, through 

 which the point on the circle rises from the line A B to its highest 

 position, is similar and equal to the arc c B through which it descends. 

 In the diagram we see small parts of the preceding and succeeding 

 cycloids. 



The principal properties of the cycloid are as follows : 



1 . P Q is equal in length to the arc c P. 



2. The tangent at Q is parallel to the chord c P. 



3. The arc c Q is twice the chord c p, and the whole arc A c B is four 

 times c E, the diameter of the generating circle. 



4. Complete the rectangle C<JR; the area cqu is equal to the 



