sn 



CTAKOM1 



emvosni 



It i. usually h 



erl by the formula (H, Soy), 



and the other ulphocyanide by the general formula (M.ScyV 

 acid may be isolated by exposing subaulphocyanide of mercury to a 

 current of sulphuretted hydrogto. It is a colourless liquid. By expo- 

 sure to a low temperature H soUdifies to a mass of crystals. It is 

 into hydrocyanic acid and kydnperttjpfio- 



(K, Soy) is formed by fusing together 

 sulphur and cyanide* of potassium, or by heating in a covered crucible 

 at a dull red heat a mixture of 44 parte of dried ferrocyanide of potas- 

 sium. 84 of sulphur, and 17 of pure carbonate of potash. The cooled 

 mass is digested in water, filtered, the filtrate evaporated to dryness, 

 and the residue digested in hot alcohol. On cooling, the liquid 

 deposit* the salt in beautiful crystal*. 



Other sulphocyanides are obtained by double decomposition with 

 the potassium salt. The sulphocyanide* of barium, calcium, ami iron 

 are soluble; those of mercury, lead, and silver are white insoluble 

 precipitate*. Soluble sulphocyanides give, with ferric salts, an intense 

 red solution, owing to the formation of persulphocyanide of iron. This 

 reaction U characteristic. 



Chlorine and nitric acid act upon sulphocyanic solutions, producing 

 a yellow precipitate, the composition of which has not been satisfacto- 

 rily determined. By heat this precipitate is altered into a substance 

 called by Liebig crude nulion. [MELLON]. Jfeiam is the name given by 

 Liebig to the residue of the destructive distillation of sulphocyanide of 

 ammonium. [MELAM.J 



Cyanogen and tehnium form combinations corresponding in compo- 

 sition and properties to the sulphocyanic compounds. 



Metallic Iteriration* of Cyanogen. Cyanide of potassium forms double 

 salts with the cyanides of cobalt, copper, iron, chromium, platinum, 

 and iridium. It is usually assumed that in these salts the potassium 

 is combined with electro-negative compound salt-radicals, to which 

 have been given the name* tobalticyanoyen, euproeyanogen, ferrocyano- 

 gen, chromieyanogett, platinoeyanogen, platinideyanogen, and trirfio- 

 eyanogen. Some of these are monobasic, some dibasic, and others 

 tribasic. They form, with hydrogen, a well-marked series of acids. 

 The following list of these acids, with their formulae, will at once 

 indicate their constitution : 



Hydroplatinoeyanic acid 

 Hjdroiridiocyanic acid 

 Hy<lr..phuinidcynic acid 

 Hydroferrocyanic acid 

 Hydroferridcyanic acid 

 Hydrocobalticyanic acid , 

 Hydrochromicyanic acid 

 Hjdrocuprocyanic acid 



H, Pt Cy, 

 H,IrCy, 

 H,, Pt.Cyj 

 H,, Fe.Or, 

 H a , Fe,Cy. 

 U s , Co.Cv. 

 H,, Cr.Cy. 



Tho methods of preparing the most important of the above acids 

 will be found described in the articles on the different metals that 

 enter into their composition. 



By the replacement of the hydrogen in these acids by an equal num- 

 ber of equivalents of a metal, a numerous class of salts is formed, some 

 members of which are largely used in the arte. Thus, by substituting 

 the two equivalents of hydrogen in hydroferrocyanic acid by two of 

 potassium, we obtain ferrocyanide of potassium (K,, FeCy., or K,Fcy), 

 the common yellow prussiate of potash. From hydroferndcyanic acid 

 (H,, Fe,Cy v or H,, Fdcy) we derive ferridcyanide of potassium (K,, 

 Fe,Cy., or K,Fdcy), ordinary red prussiate of potash. For details of 

 the preparation of the principal of these salts, see the various metals. 



Ji ydronitnferrofj/anic acid, or hydronitropruttic acid (H .,Fe 1 Cy,NO J ), 

 is produced when binoxide of nitrogen (NO,) is passed through a solu- 

 tion of hydroferridcyanic acid. The decomposition that taken place is 

 thus expressed : 



HiFiCr. + NO, 



II,, Fe,Cy,NO, + HCy 



lljdrofcrridcyanic Binuxide Hydronitropriuiic Hydrocyanic 

 acid. of nitrogen. acid. acid. 



Hydronitroprussic acid may be obtained in prismatic crystals of a 

 deep red colour, containing two equivalent* of water. .\ ', r i-iairidti, 

 containing two equivalents of a metal in the place of the hydrogen in 

 the acid, are readily formed. The sodium salt crystallises in fine ruby- 

 red prisms; the barium salt in beautiful octohedra. For details of 

 the preparation of these salts, see papers by Playfair in the ' Philo- 

 sophical Transactions,' 1849 and 1850. 



The characteristic test for nitroprussides is the production of a 

 beautiful purple colour on thu addition of an alkaline sulphide. Traces 

 of sulphur on the one hand, or of a nitroprusside on tin' other, ma\ 

 thus be detected with certainty ; the colour in however very fiu 



NiiMKTKH, from the Greek words xvaris (blue) and ftfrpoy 

 (a measure), is an instrument which was invented by M. de Saussure 

 for the purpose of enabling an observer to mixture the intensity of Ue 

 colour in the sky. 



It is well known that the visible heavens, when free from clouds, 

 appear to have a blue tint which gradually increases in intensity from 

 the horizon towards the zenith, that the blueness is more intense by 

 night than by day, and that on the tops of mountains the colour is 

 sometimes so deep as to be almost black. These appearances depend 

 partly on the different extents of atmosphere which the rays of tight 



have to pass through, and partly on the quantity of water which the 

 air holds in solution. It has been supposed that the gaseous tuid, air, is 

 of a bUe colour ; the colour being so slight as to be seen only when we 

 look through large msssu of air; and that it U to this cause that 

 distant mountains owe their peculiar bluish tint When, as towards 

 the senith, the atuxvpherio space traversed by the light is compara- 

 tively small, the violet and blue rays are transmitted to the earth in 

 abundance; while, towards the horiaun, the spaces passed through 

 being greater and being charged with vapours, the violet, the blue, and 

 even toe green rays are intercepted, the remaining colours only of the 

 spectrum being transmitted : it must, however, be added that the 

 colour of the sky is affected by the terrestrial particles which are 

 occasionally raised in the atmosphere ; and also by the reflections of 

 light from terrestrial objects, particularly from naked rocks and from 

 masses of snow or ice. The colour of the sky being thus, in son* 

 measure, an indication of the state of the atmosphere with respect to 

 exhalations and the reflections of light from the earth's surface, it is 

 of importance to ascertain with some precision the intensity of that 

 colour. 



The cyanometer, as formed by the inventor, consists of a circular 

 plate or ring, of metal or pasteboard, on the surface of which, 

 the circumference, is a band divided by radii into fifty-three equal 

 compartments. One of these is white, and those which follow in suc- 

 cession are coloured with blue of different degrees of intensity, fruui 

 the most faint to the deepest which can be produced ; the rest 

 compartments are coloured with mixtures of Prussian blue and ivory 

 black, and gradually increase in darkness to the last division, which is 

 quite black. 



In using the instrument, the observer, who should be in the open 

 air, holds it up between himself and that part of the sky of whk-h Ill- 

 intends to ascertain the colour ; and this part should be xtich that, 

 while the face of the instrument is strongly enlightened, the direct 

 rays of the sun may not fall upon it : on turning the plate or ring in 

 its own plane, till there is brought directly before the observed part of 

 the sky that compartment which, to the eye, appears to be exactly 

 equal to it in intensity of tint, the number of the compartment will 

 express the required intensity of the blue colour in that part of 

 the sky. 



In order to form a scale of numbers for the tint*, M. de Sauasure 

 placed against a wall a piece of white paper, on which was a circular 

 Mack spot, about one-seventh of an inch in diameter, and receded from 

 it till the spot ceased to be visible ; he then laid on paper a tint pro- 

 duced by Prussian blue, BO diluted that, at a distance from it equal to 

 that at which the black spot became invisible, the tint could not be 

 distinguished from a perfect white. This tint was marked No. 1. 

 The next deeper colour was produced by diluting the Prussian blue 

 till, at an equal distance, the tint ceased to be distinguished from that 

 of No. 1, the latter being near the eye : this was marked No. 2 ; and 

 each of the succeeding numbers up to No. 63 was determined in like 

 manner by a comparison of the corresponding tint with that which 

 preceded it on the plate. 



Arago invented a cyanometer, which acts on the same principle as 

 his photometer. The latter instrument is thus formed : Two lenses 

 are placed, one on the other, so as to form coloured rings about 

 the point of contact, which, as is well known, are seen as well by 

 transmitted as by reflected light, the one set being complementary 

 to the other. These two series of rings neutralise one another 

 mutually when the two lights which form them, and which fall simul- 

 taneously on the lenses, are of equal intensity. His cyanometer is an 

 extension of this principle. It is formed of a tube closed at 01 

 by a plate of rock-crystal cut perpendicularly to its axis, and, at tin- 

 end nearest the eye, by a doubly refracting prism. Among the colours 

 which this apparatus gives, when polarised light traverses it, and the 

 prism is turned on its axis, is the peculiar blue colour of the >ly, 

 which varies in intensity according to the proportion of polarised light 

 admitted by turning the prism. 



Suppose now that this polariscope be directed upon a piece of white 

 ]!!, and that between the paper and the plate of rock-crystal there 

 is placed a pile of plates of glass, which can lie moved in an angle, so 

 as to van- their inclination, and make the bright light from the paper 

 more or less polarised. Tho blue colour seen in the instrument goes 

 on increasing in intensity with the inclination of the pile, until it 

 appears the same as that of the region of the sky which weaie oh 

 serving. The measure of this cyanometric tint is then given by the 

 inclination of the- pile, and if the pile be composed of the same nu 

 of plates, and the same kind of glass, the observations made with this 

 instrument will be of course comparable. 



CYANOSIS, or BLUE DISEASE, u & condition f the 



which comes on as the result of a malformation of the heart, which 

 allows the venous and arterial blood to mingle in the syst . 

 fiotus the circulation is of such a kind as to prevent the Mood H 

 from the placenta passing through the lungs, and thi> is doim by a 

 communication between the pulmonary artery and the aorta the 

 tlHCttu arlcrioiia ; and an opening between the right and left ventricle 

 the fvramcn male. After birth these two communications between 

 the right and left side of the heart are normally closed, but it occa- 

 sionally happens that one, or both, passages do not close at birth or 

 that they open again in after life. The consequence of this mal ' 



