Pkihfophkal and Ecofism'ical Vfes o/Cktomt,- 445- 



S E C T I O N X. 



JJfes of Chrome, of the Oxide of Chrome, and of the Chromic Acid, 



THE brittlenefs of chrome, its refiftance to the aftion of fire, and the fmall mafles In 

 which it has hitherto been found, afford little expedlation that this metal will ever be of 

 great ufe in the arts. But this afTertion may be too ftrong ; for a new fubftance, of which 

 the properties at firft appear to be of fmall intereft to fociety, is fometimes found, in the 

 fubfequent procefles of inveftigation, to be capable of very important applications in the 

 irts and fciences. 



The acid and the oxide of this metal are certainly not fubje£l to the fame obferwitlon. 

 The former, by the beautiful emerald-green which it communicates even to enamels, with- 

 out being fubjc£t to alteration in the purity of its ftiade, will afford to painters and enamel- 

 lers an additional object to enrich their produftions, and add to the perfecSlion of their art : 

 the fecond, by the beautiful cinnabar red which it alTumes and keeps in its combination 

 Vith mercury ; the orange-red colour it affords with lead ; the carmelite red it communi- 

 cates to filver, may become highly valuable for paintings in oil and water-colours. 



Chemiftry will be greatly benefited by this excellent re-agent to dete£l: the fmalleft 

 quantities of mercury, filver, and lead, diffolved in acids by the different colours it pro- 

 duces when its adlion is afllfted by an alkali. And, in the fame manner as this acid indi- 

 cates the prefence of the metals here fpoken of, thofe metals in their turn may ferve to dif- 

 cover the chromic acid, if it be previoufly put into the neceffary condition to produce the 

 before -mentioned effects. 



If the chromic acid fliould hereafter be abundantly found In any other combination be- 

 Cdes that of lead, it might, after extra£tion by carbonate of potafli, be ufed for the artificial 

 compofition of red lead, and furnifh, in abundance, this valuable orange-red colour for 

 painters' ufe, which is fold very dear in Siberia, and applied to this purpofe with great fuc- 

 cefs. For thisobjeiSt the native red lead, which is diffeminated in fmall cryftals, or plates, 

 in the fiffures of quartzofe or gritftone gangues, in which it is commonly found, might be' 

 pulverized, then boiled with a folution of carbonate of potafli, and mixed with nitrate of 

 lead ; the acid of which will faturate the potalh, and afford its metal to the new acid, which 

 will thus produce a colour no lefs beautiful than the natural, and perfcdtly clear of the 

 matrix. 



There is reafon to prefume that chrome, cither In the ftate of oxide or of acid, will be 

 found fingly or engaged in fomc other combinations. For tlie analyfis of the emerald of 

 Peru has already fliewn me that its colouring part Is afforded by the oxide of this metal ; » 

 circumftance which gives the moft agreeable proof of the goodnefs and fixity of this colour, 

 as it is known that the emerald can fuftain the moft violent degree of heat without lofing 

 Its colour. 



. I have likewife found that the yellowilh green tufted cryftals, which often accompany the 

 rod lead ore of Siberia, are'fotmed of chrome and lead, both united, in the ftate of oxide. 

 Green cryftals poffeffing the fame form, the fame dimenfions, and the fame fituations on 

 the matrix as thofe of red lead, but which are a combination of the oxides of chrome and 

 <jf lead, are likewife found in certain fpecimens of the native red lead. It is probable that 

 tluefe combinations originally exifted in the ftate of chromatc of lead, and that in procefs- 

 y«t. 11.— Jan. 1793. - 3 M mi 



