1852.' 



SCIENTIFIC INTELLIGEjSiCE. 



115 



and a geueval exposiliou uf the prugress of science in its several 

 (lepartinents. 



This Joiireal was cstablislied in 1819 by Professor SiUiman, and has 

 reached its 34th year. A Second Series was commenced, January, 

 1846, and the IStli volume of the new series begins with the number 

 for January, 1853. We commend tliis Journal to the attention and 

 substantial support of all fi-iends of science. 



SCIENTIFIC INTELLIGENCE. 



" On the OrriCAL Properties of a eecently-discovered Salt of Quin- 

 IXE "by Prof. Stoics.— This salt is described by Dr. Herapath in Uie Phil- 

 osophical Mao-azine. and is easily formed in the way there recommended 

 namely by dissolving- disulphate of quinine in warm acetic acid, 

 addino-'a few drops oin solution of iodine in alcohol, and allowing tlie 

 Uquid''to cool; when tlie salt crystaUizes in thin scales, reflecting 

 (while immersed in the fluid) a green light with a metallic lustre. 

 Wheu taken out . if the fluid the crystals are yellowish green by re- 

 flected li"lit with a inclallic aspect. The following observations were 

 made wifli s'ninll cvvsials formed in this manner -.—The crystals pos- 

 sess in an ciniiu'iii ilr-rce the property of polarizing light, so that Dr. 



Heinpitli prnpo-r.! iiiploy them instead of tourmalines, for which 



they woul'l form ,in :iamivable substitute, could they be obtained in 

 sufficient size They appear to belongto the prismatic system : at any 

 rate thcv are symmetric il (so far as relates to their optical properties 

 and' to tl"ic directions of their lateral faces) with respect to two rectan- 

 gular pianos iierpcndicular to the scales. These planes wiU here be 

 called respectively the principal plane „f the length and the principal 

 plane of the brcadUi, the crystals being nsuaUy longest in the direction 

 ofthe former plane. When the crystals are viewed by hght directly 

 ti-ansmitted, wliich is either ptdarized before incidence or analyzed 

 after transmission, so as to retain only light polarized in one of the 

 principal planes, it is f-mnd that with respect to Ught polarized in the 

 principal plane of the length the crystals are transparent and nearly 

 colourless —at least when they are as thin as tliose which are usually 

 formed iiv the method above mentioned. But with respect to hght 

 polarized in the principal plane of the breadth, the thicker crystals are 

 perfectly black, the thinner ones only transmitting light, which is ot a 

 deep red colour. Wien the crystals are examined by the light reflected 

 at the smallest an"-le witli which the observation is practicable, and the 

 reflected li'dit is analyzed, so as to retain,— first, light polarized in the 

 leno-th and secondly,' light polarized in the other principal plane,— it 

 is fSuud that in the first case the crystals have a vitreous lustre and the 

 reflected Ught is colouiless, while in the second case the bg" is yel- 

 lowish green, and the crystals have a metallic lustre When the plane 

 of incicfeuce is the principal plane ofthe length, and the angle of inci- 

 dence is increased fromO= to 90 ° , the part of the reflected pencrl 

 wliich is polarized in the plane of incidence undergoes no remarkable 

 chano-o except rc-.linns iliat the lustre becomes somewhat metiiUic. 

 When the part wlu.l, i> p.Kaiizcd in a plane perpendicular to the foraier 

 is examined it is \uu:n\ ihat the crystals have no angle of polarization, 

 the reflcted' U"lil ii.vrr vanishing, but only changing its colour, pass- 

 in «■ from y.ll.rwisli "iven, which it was at first, to a deep steel blue, 

 which colour it ;i~-iiiiifs at a considerable augle of incidence. When 

 the li"ht reil.-nc.l iu Uii' p'iuoipal plane of the breadth is examined in 

 asimriu- niaunev tlu' i.-n.il which r- polarized in the plane of incidence 

 uuder"ocs m reinavk'ali'.r rl.an^c, continuing to have the appearance 

 of beiu<' reflected IVmn :i nntai, wlille the other or colourless pencil 

 vanished at acerlr.in ;m,_;I. ,,nd afterwards reappeai-s, so that m this 

 plane the crystals luv. a p.larizhig angle. It then, for distinction s 

 sake, we call the two peu.ils which the crystals, as belonging to a 

 doubly refi-acting medium, transmit independently of each other 

 ordiniru and extraunlinary. the former being that which is transmitted 

 with little loss, we may say, speaking approximatively, that the 

 medium is h-ansparent witli respect to the orSmary ray, and opaque 

 with respect to the extraor.linary ; while as regards reflexion, the 

 crystals fiave the properties of a transparent medium or of a metal 

 according as the refracted ray is tlie ordinary or the extraordmary. If 

 common Uoht merely be used, both refracted pencds aic produced, 

 and the corresponding; refleeted pencils are mixed together; but bv 

 analvzin- the ,vHeri,.,l li-l.l-. by n.ear.s uf n ^u-ul■s pns,,,, the reflected 

 DenJils mn- be view.. I M'n;.v;ii'rlv,-;il le;i,t ^yllen the observations are 

 Sinedr.hep=i.-,>M p'laues. ' The eryst.ls are n„ doubt biaxal, and 

 the pencils here e;ill.d oidin;iry and extraordinary are those which in 

 the lano'uao-e of tie ore eon, -pond to different sheets ofthe wave sur- 

 face fhe^reflcetiu"- pioperiies of the crystals may be embraced m one 

 view by regardh.g" the medium as not only doubly refractmg and 

 doubly "absorbing, but donbh/ metallic The metallicity, so to speak, ot 

 the niedium of course alters continuously with the pomt of the wave 

 surface to which the pencil considered belongs, and doubtless_ is not 

 mathematicallv null even for the ordinary ray. If the reflection be 



really of a metallic nature, it ought to produce a relative change in the 

 phases of vibration of light polarized in and perpendicularly to the 

 plane of incidence. This conclusion the author has verified by means 

 of the effect produced on the rings of calcareous spar. Since the crys- 

 tals were too small for individual examination in this experiment, the 

 observation was made with a mass of scales deposited on a flat black 

 surface, and arranged at random as regai-ds the azimuth of their prin- 

 cipal planes. The direction of the change is the same as iu the case of 

 a metal, and accordingly the reverse of that which is observed in total 

 internal reflection. In the case of the extraordinary peucU the crystals 

 are least opaque with respect to red light, and accordingly they are 

 less metallic with respect to red light than to light of higher refi-angi- 

 bility. This is shown by the green colour of the reflected light when 

 the crystals are immersed in fiuid ; so that the reflexion which they 

 exhibit as a transparent medium is in a good measure destroyed. The 

 author has examined the crystals for a change of refrangibiUty, and 

 found that they do not exhibit it. Safllower red, which possesses 

 metallic optical properties, does change the refrangibility of a portion 

 of the incident light ; but the yellowish green light which this sub- 

 stance reflects is really due to its metallicity, and not to the change of 

 refrano-ibility, for the light emitted from the latter cause is red, besides 

 which'it is totally different in other respects from regularly reflected 

 Unlit In conclusion, the author observed that the general fact of the 

 rellection of coloured polarized pencils had been discovered by Sir 

 David Brewster in the case of chrysammate of potash ;* and in a sub- 

 sequent communication he had noticed in the case of other crystals the 

 difference of effect depending upon the azimuth of the plane of inci- 

 dence.t Accordingly, the object of the present communication was 

 merely to point outthe intimate connexion which exists (at least iuthe 

 ca.se ofthe salt of quinine) between the coloured reflection, the double 

 absorption, and the metallic properties of the medium. 



Specimens of Sensitive Media were exhibited by Professor Stokes. 

 These were : — a crystal of green fluor spar, which, by the developc- 

 ment of blue light within it, changed its colour ;— the solution of the 

 common disulpliate of quinine in acidulated water, which, b^^ its action 

 on the invisible rays developed blue light; and the solution if the 

 green colouring matter of leaves in alcohol, which by a siniila- action 

 became blood red. 



Reduction of Metals et Phosphorus axd SirLPnuR. — It had been 

 observed by Woehler that phosphorus in combination with copper 

 excites an electrical current. M. Wicke has made the following 

 observations : — 



1. A stick of phosphorus wound round with a strip of silver was 

 placed iu a highly concentrated solution of nitrate of silver. The sUver 

 and phosphorus instantly became covered with a blackish film ; after- 

 wards silver began to be reduced in a wart-like form upon the strip of 

 silver ; and after the lapse of a few weeks it was covered with an ex- 

 tremely shining coating of crystalline silver, although not in immediate 

 contact with the phosphorus. The whole of the reduced silver could 

 be removed from the strip of silver as a compact coating with a shining 

 inner surface. The phosphorus was only covered superficially with a 

 thin coating of dark phosphuret of sUver, and remained unchanged 

 internally, The silver separated so evenly, and with such a shining 

 surface, that this process might perhaps be employed for galvano- 

 plastie purposes. 



• 2. In a similar manner, by a combination of phosphorus and lead in 

 a solution of nitrate of lead, the reduction of crystallized lead took 

 place upon the lead, whilst the phosphorus was covered with a thin 

 black film ; the action, however, was weak, and soon stopped 

 altogether. 



3. A stick of phosphorus was placed on the axis of a closely-pressed 

 mass of oxide of copper, both covered with water, with which the tube 

 was filled, and then made air-tight ; the reduction of the oxide to 

 metallic copper was gradually effected, so that after several weeks the 

 stick of phosphorus, which was still remaining, was surrounded by a 

 capsule of crystalline copper. 



4. Sulphur, surrounded with a strip of lead, and laid in solution of 

 nitrate of lead, effected the reduction of lead upon the lead in form of 

 a loose crystalline coating. 



5. When a piece of sulphur. suiTounded with a bright copper wire, 

 was laid in a saturated solution of sulphate of copper, it became 

 covered after some time, in the place where the copper touched it, 

 with a loose crystalline coathig of indigo-coloured sulphuret of copper, 

 whilst the copper wire was dissolved. A solution of mtrate of copper 



• Report ofthe Meeting of Ihe British Asaociation al Soutliamplon in 1S46, 

 Pari II., p. 7. 



\ Ditto Oxford, 1S47. 



