i HKOMIVM. 





powerful furnace. More recently, M. Kreiny hu obtained the meUl in 

 crynuU iHieing great brilliancy. They belong to the cubic system, 

 are very bard, and not acted upun by even the rtrongert. acids. The 

 cry.taJa were formed oil passing sodium vapour, by moans of a stream 

 of hydrogen, over the anhydrous chloride heated to reduces. 



By heating the sesquichlorido of chromium with potassium, and 

 washing the product with water, an allotropic inmlitii j-. u the 

 metal ii obtained. It present* the appearance of a dark gray i 

 that under the burnisher assumes a metallic lustre. Heated in con- 

 tact with air, it takes fire at a temperature below redness, and I -urn* 

 with considerable brilliancy, yielding seaquioxide. It is rapidly acted 

 upon by acids, hydrochloric or duute sulphuric dissolving it with 

 cM'lution of hydrogen gas. 



Chromium U of a light gray colour ; its specific gravity U about 5'9. 

 It U very brittle, noii volatile and non-magnetic. From the difficulty 

 of preparing it in the metallic state, a* well on on account of its com- 

 parative scarcity, this metal has iit yet received any application iu 

 the arts. 



livalunt, 2"27. 



Chromium and o-rygen combine to form several compounds. The 

 inoet ini])ortnnt arc four in number : 



Formula. Kiiuivalcnt. 



Proloxld* of chromium . . . CrU 34-3 



Snquioxide of chromium . . . Cr,O, 76-5 



Chromic tcid .... CrO, 



Pcrcl.romic acid . ... Cr,O, 10.VS 



To these may be added ckromoto-chromic iu-ulc (Cr^O,), corresponding to 

 magnetic oxide of iron, and four other oxides, which may be viewed as 



"iitions of soKquiuxidc of chromium with one, two, three, or four 

 equivalent* of chromic 



rnit.r!il- i,f f/ir-iiii nun (CrO) cannot be obtained in tlie anhydrous 

 rondition. The hydrate (CrO,HO) is precipitate! when cau.-tic potash 

 is added to a solution of protochloride of chromium. Its colour is 

 dark brown. It is a very unstable compound, rapidly al 



ii. and >>ecoming converted into a higher oxide, Ky careful 

 manipulation it maybe made to form salts with several of the acids. 

 The double sulphate of pr"to\ide of chromium and potash (CrO, 80, 

 + KO, SO, + 8Aq) forms crystals of .1 fine blue colour. 



"ioxidt of chromium (Cr, 0,). For usi: in enamel painting and 

 glass staining : this is best prepared by heating eliminate of mercury to 



s; metallic mercury and oxygen are given off, and tin 

 oxide remains as a deep green powder. It may also be obtain. -1 1>\ 

 heating bichromate of potash with carbonate of potash and chloride 

 of ammonium, or with sulphur only, or with charcoal, or, finally, by 

 heating bichromate of potash alone; in the latter case the following 

 deconi|H>sition takes place : 



2 (KO, 2 CrO,) = Cr.O, + O, + 2 (RO. CrO,) 



Bichromate cf Srquioxiclc Oxygen. Neutral Chromnte 

 Potash, of Chromium. of Potash. 



The oxide thus prepared presents a beautifully crystalline appear- 

 . 



The hyilralal KJiquioxide ol chromium ((.'r^i. , 10l( >> is a grayish- 

 green precipitate ; and when v adding solution of ammonia 

 to a cold solution of a violet > 'of chromium, i* then soluble 

 in ammonia, acetic acid, or dilute solutions of poi.-i-h ; dissolved in 

 strong acid* violet-coloured solutions arc obtained. I'ndcr other cir- 

 cumstances, however, hydrated seaquioxide of chromium possesses 

 properties the very reverse of those just mentioned ; its composition 

 remains the same, but it is no longer soluble in ammonia, acetic acid, 

 or dilute solutions of potash ; a distinct isomcric condition is set up. 

 Very alight causes are sufficient to effect this modification ; thus the 

 action of boiling water, desiccation in the open air, or even iu vacuo 

 after some time, or mere friction, are, according to M. Fremy , m . 

 to determine this change from the soluble to the insoluble variety. 



The naltt of the faqtuoxide of chromium, like the sesquioxido itself, 

 exist under different uomeric modifications. Thus lulfilmtf of /,. 

 is obtained of a violet colour, when eight parts of hydratod oxi<! 

 at 212 are digested with nine parts of concentrated sulphuric: acid in 

 a shallow vessel for two or three weeks ; at the end of that time the 

 mixture is usually converted into a mass of crystal* having tit 



n (Cr,O,,3SO,, 15HO). With the sulphate of potash, this 

 variety forms a beautiful violet-coloured double salt called ehnnnr 

 alum, from the fact that it is in all respects similar to common alum, 

 except that it has chromium in the place of aluminium. [ Ai.rxs.] 



The grttn mlphatc of chromium U formed when solution of the 

 violet sulphate u boiled ; it u unorystallisablc. 



A red anhyilroiu sulphate (Cr,0,, 880,) is obtained in crystal* win n 

 cither nf the preceding sulphates are heated to about 700. It is quite 

 insoluble in water, or concentrated acids ; long contact with water, 

 however, converts it into the soluble vai 



The other salts of scsquiozide of chromium are comparatively unim- 

 portent: in general properties the sulphate is a type of thu 

 rwmy distinguishes those of a violet colour as mitt of met<i' 



IxMe possessing a green tint a* *ili of the ordinary 

 oxide. When the former an converted into the latter by ebullition 

 no alteration in chemical composition takes place, the change is entirely 



due to the isomeric modification .[ tin- dned in them as 



before adverted to. 



Tartratfofrin,,,: 

 drated sesquioxide of chromium in soli M 



ng liquid is deep green by reflect, 

 mitted light 



<nik ofekroninn (Cr.O^HO.C.H . 



-id (C.H, (Cr,O 

 . an fi|r,i\alent of hydi< 

 iate of potash is pre]>ared by adding powdci 

 hot aqueous solution of bichromate of potash till evolution 

 ises ; the re-action is somewhat couiplic 



i with acetate of lead, a bluish K" " pi. < ii'itat.- of chroni" 

 t,n trate of lead U produced, and from this by 

 sulphuretted hydrogen the chromotartari 



CAfi '<',) crystallises in beautiful -dies on tip- 



cooling of a mixture of about four parts of a saturated M>IU- 

 bichromate of potash, and five parts of c. nnutr.it. d xui 

 on pouring off the mother liquor and draining the i-ry.-t.iK f. 

 time on a porous tile, they are obtained nearly pure. 



Chromic acid is anhydrous. On being heated it fir.-t blackens, at 

 about 400 fuses to a bright reddish-brown liquid, and at a higher 

 temperature is decomposed iut" oxygen and sesquioxidc of chromium. 

 Exposed to the air it rapidly deliquesces. It has a Hour, xomewhat 

 rough taste, no odour, stains the skin yellow, and rapidly ox 

 organic matter. 



VhnmaUf, formed by the union of chromic acid with Kw, iK-.-ur in 

 three classes, basic, neutral, and acid ; tin- </ 



chmnw), containing two equivalents of oxide of lead to one of chromic 

 acid (2Pbo,CrO,) is a familiar instance of a basic chru: 

 ckromate of lead (chrome yelloic) (Pbo, CrO,) is a well knon r\amph- 

 of a neutral chrouiatc; while liir/trimml,: nf ymfux/i (KO, 'JCrOj) is a 

 type of acid eliminates. For details of the preparation an 

 of the chromates, see the various metal.-, ! X.iv. . 



1'oTASstr.M, &c. : also an excellent paper 'On the. mannfart 

 chromate and bichromate of potash, chroinate and L: f soda, 



ehromate of liuie, chromate and diehromate of lead, ehromato of zinc, 

 chromic acid, &c., &c.;' in the ' Pharmaceut I,' vol. .\v., 



pp. 32 and 66. 



Bieliruamte of \ ijuanlity of chromic acid :.s ilivid. 



two portions, the one neutralised with ammonia and the.-ce nd i 

 then added. On evaporating the .-olr.ii"ii over strong sulphuri 

 biehromate of ammonu crystal! iseis, under the form of cherry red 

 ing a few crystals of this salt, placed in a crucible 

 caisible. of containing twenty or thirty times the quantity, to the flame 

 of a lamp, a very energetic action with incan- 



descence, and the crucible is filled with seaqujoxiae of chromium, iu 

 a form in which it presents a perfect rcsemMance to green tea. 



The source of all the salts of i hi of course 



art, which is oxidised cither by a nitrate or more cimply by atmo- 

 spheric air. 



acid (Cr t O,) is formed whenever an aeneous solution of 

 peroxide of hydrogen is brought into contact with ehromie acid. The 

 liquid assumes a deep blue colour, but is rapidly d. eomp. .-,-d with 

 evolution of oxygen ; if, however, the solution be agitated witb 

 the acid is withdrawn from the aqueous portion, and 

 unite with ammonia or certain organic bases to form tolerably 

 compounds. Strong acids decompose the pcrchromatcs, 

 blue perchromic acid. 



Chromium and chlorine combine to form a prot<ichl"ridc 

 sesquichloride. 



Protudiloride of chromium (CrCl) is formed on passing a CUTP 

 dry hydrogen gas over the eflMuichlorido. heated t . rodnm. ; 

 chloric acid is given off, and the protochloride remains as a white 

 powder. It is soluble in water, yielding a blueish green solnti. 

 rapidly absorlis oxygen from th 



Setquickloridt of cltromium (Or a Cl,) is a very beautiful sub- 

 having the form of transparent plates, in colour resembling, but 

 what darker than, peach blossoms. It is readily obtained 

 current of dry chlorine gas over a mixture niinin 



and charcoal heated to redness in a porcelain tube ; the *- 

 l ing volatile, sublimes and condenses in the 

 tube. It is scarcely altered by even long air, and I: 



is quite insoluble in water or iu acids; the presence, In 

 trace of protochloridc renders it easily soluble. Solution of 

 chloride of chromium is most readily made l,y dc<.\idi>ing a solution of 

 bichromate of potash, < acid, with 



dcohol or sulphit hition 



may !' with amn 



washed and dissolved in hydrocld'i 



ChliirncJironic <v'"l always results when hydroehlori.', snlphni : 

 chromic acid ' together ; the presence of any water prevents 



the re-action. To prepare it in the pure state, 10 parts of chloi 

 sodium are fused with 17 part* of neutral chromate of ]iotasli ; when 

 e..ld, the mass is broken up, placed in a retort, and .",0 parts of the 

 strongest sulphuric acid added ; on gently mixing the ingredients, 

 -nlfieieiit heat is geiii'i.,|e.l \, t volatilise the ehlorochromic acid, which 

 distilii over, and may ! condensed in a cooled receiver. 



