Vol. XXIl. No. 5.] 



POPULAR SOTIEKOT^ KEAVS. 



69 



Pratttcal €l)einietrp anH tl)e Slrts. 



♦ 



GLASS AND PORCELAIN PAINTING. 

 The manufacture of both glass and pot- 

 tery dates back to prehistoric times, and we 

 have no knowledge of either the first glass- 

 maker or potter. Whoever these individuals 

 maj' have been, they could not have practised 

 their art very long before noticing that certain 

 impurities in their materials gave a more or 

 less brilliant color to the finished product. In 

 time they doubtless learned to recognize and 

 select the earths which produced the highly 

 prized hues, and from this rude beginning 

 the modern art of vitreous ornamentation has 

 arisen. 



The principle of both glass and porcelain 

 painting are the same, and onlj' vary in the 

 practical details. Porcelain-painting is really 

 glass-painting, as the colors are usually melted 

 into the glaze or film of glass which covers it, 

 or else the colors themselves are mixed with 

 materials which form a glaze when melted. 



It has been found, that, when certain metallic 

 oxides are melted into glass, they unite with it, 

 forming metallic silicates or analogous salts, 

 which in many cases show the greatest beaut}' 

 and brilliancy of color. It is a very pretty 

 experiment to melt a little borax in a crucible, 

 and, after it has cooled, it will be perfectly 

 transparent and colorless ; then add a minute 

 quantity of some salt of cobalt, and fuse again, 

 when the whole will become of a magnificent 

 blue color. Other substances give different 

 tints : thus, oxide of iron can give red, brown, 

 violet, and yellow ; chromium gives a beautiful 

 green ; manganese, violet, brown, and black ; 

 antimony and lead, j-ellow ; copper, green and 

 red ; silver, red and yellow ; gold, a beauti- 

 ful rub}' red. Platinum and iridium give a 

 fine black, and gilding or silvering is accom- 

 plished by melting the metals themselves into 

 the glaze. Certain salts of gold also have the 

 [iroperty of reducing to the metallic state in 

 the firing, producing a very brilliant gilding. 

 These different colors are so characteristic that 

 a system of chemical analysis has been founded 

 upon them, and the chemist can often save 

 himself much time and labor by noting the 

 color of a borax " bead " in which a little of 

 the substance under examination has been 

 melted. 



The actual preparation of colors for porce- 

 lain-painters is a much more difficult matter 

 than the above facts would seem to imply. 

 Much experiment is necessary to obtain all 

 the different shades and intermediate tones. 

 Unlike oil paints, the method of simple mixing 

 cannot be followed. A mixture of blue and 

 yellow in mineral colors, for instance, may 

 give, after firing, any thing but the green tint 

 which a similar mixture of oil or water-colors 

 would produce. Such points can onlj' be de- 

 termined by actual trial. 



The composition of many of the most beau- 

 tiful colors is kept a carefullj' guarded secret 

 by the manufacturers possessing the recipe. 

 The dark-blue tint of Dresden porcelain was 

 for a long time such a secret, and may still 



be so, although a few j'ears ago we were in- 

 formed at the Meissen Pottery that it was sim- 

 ply cobalt. Other unknown ingredients may, 

 however, be added to it. The' softness and 

 delicacy of a fine painting on porcelain or glass 

 cannot be surpassed b}' any work in oil or 

 water-color, and it possesses the additional ad- 

 vantage of being indelible and unchangeable 

 by those natural agencies which will in time 

 destroy the more perishable paintings on paper 

 and canvas. 



NEW METHODS IN ANALYSIS. 



In a former article a description of a new pro- 

 cess for the separation of iron from nickel was 

 given, depending upon the formation of ferro- and 

 nickelo-cyanide of potassium, and of their differ- 

 ent reactions with bromine. Since then, however, 

 the process has been modified and altered without 

 affecting the accuracy of the results, so as to avoid 

 the use of phosphoric acid, the presence of which 

 might complicate matters, and at the same time to 

 admit of its application to other separations. 



Nickel frovi Iron. — To the cold concentrated 

 (twenty to thirty cubic centimeters) and slightly 

 acid solution add an excess of solid sodic hydro- 

 carbonate, in such quantity, that, after stirring, a 

 little remains undissolved, and nickel and iron both 

 appear to be thrown down. Now add potaasic cya- 

 nide until the precipitate dissolves, then heat gently 

 until the pale- yellow color of the ferrocyanide is 

 produced ; at this stage the solution should be 

 perfectly clear and free from any ferric hydroxide. 

 Allow the liquid to cool ; add a considerable quan- 

 tity of a rather strong solution of potassic hydrate ; 

 then treat with chlorine, continuing the current of 

 the gas until the green nickelous hydrate is com- 

 pletely converted into the nickelic hydrate, and 

 becomes perfectly black, after which it may be fil- 

 tered off, and treated in the usual manner for elec- 

 trolytic deposition. 



Alumina from Iron, Nickel, or Cobalt. — Proceed 

 exactly as above, and add a few drops of potassic 

 hydrate to the somewhat turbid yellow solution 

 until it becomes perfectly clear ; then boil with the 

 addition of ammonic chloride, when the alumina 

 will be precipitated free from any of the other 

 accompanying metals. The potassic hydrate and 

 cyanide, as well as the sodic hydrocarbonate for 

 this separation, should be tested for alumina and 

 silica, — impurities almost invariably present. 



Manganese from Iron, Nickel, or Cobalt. — Add 

 excess of sodic hydrocarbonate and potassic cya- 

 nide, as already directed, and warm gently until the 

 solution — which in presence of manganese has a 

 dirty blue-green color — becomes pale yellow and 

 quite clear ; then allow to cool, add a little potas- 

 sic hydrate, and precipitate the manganese as per- 

 oxide by adding a little peroxide of hydrogen, and 

 leaving the solution in a warm place for a few 

 hours. The peroxide, as is usual when precipi- 

 tated from alkaline solutions, contains alkali, from 

 which it is very difficult to free it by washing; so 

 that it is best to dissolve in hydric chloride, and 

 precipitate as carbonate with ammonic carbonate. 

 In order to avoid this inconvenience, the cyanide 

 solution may be precipitated by sulphuretted hydro- 

 gen, when manganese sulphide is rapidly and com- 

 pletely thrown down, and admits of being easily 

 washed free from impurities. 



Iron from Zinc. — Procure a solution of the cya- 

 nides as above, and boil the clear solution with an 

 excess of colorless ammonic sulphide until the 

 steam is neutral to test-papers. The zinc is wholly 

 precipitated as sulphide quite free from iron (or 

 nickel and cobalt i^jjresent), and in a granular 



condition, which may be filtered and washed with 

 the utmost ease. 



The presence of cyanates or carbonates in the 

 potassic cyanide exerts no influence whatever on 

 the above separations. — Thomas Moore, in Chem- 

 ical News. 



♦ 



LIQUID AMALGAM. 



An interesting account of a series of experiments 

 upon the so-called alloy between the metals sodium 

 and potassium is given by M. Joannis in the cur- 

 rent number of the Annales de Chimie et Physique. 

 For some years it has been known, that, although 

 in many respects so similar, these two metals pos- 

 sess a certain affinity for each other, and unite 

 under suitable circumstances to form a liquid 

 amalgam-like substance. M. Joannis has at length 

 shown that a definite compound, NaKj, is formed, 

 with considerable evolution of heat, when the fused 

 metals are brought together in the right propor- 

 tion. In order to prove this fact, thermo-chemical 

 methods were resorted to; liquid mixtures of the 

 composition NaaK, NaK, NaKj, and NaK, be- 

 ing successively introduced into the calorimeter. 



The hydrogen liberated by decomposition of the 

 water in the calorimeter was caused to pass first 

 through a perforated platinum plate, and afterward 

 through a long, thin-walled glass spiral, eventu- 

 ally escaping in minute bubbles through the water 

 itself, after becoming reduced to the temperature 

 of the calorimeter. The liquid mixture of metals 

 was gradually introduced by means of an ingenious 

 apparatus consisting of a drawn-out delivery tube 

 containing the alloy between two layers of protect- 

 ing naphtha, and which, by means of a valve, could 

 be placed in communication with a reservoir of 

 compressed air, so that, by regulating the valve, a 

 gentle stream of the liquid could be forced out as 

 required. When the calorimetrical experiments 

 were concluded, the amount of alkali was deter- 

 mined in an aliquot part of the water in the calo- 

 rimeter, and thus the amount of metal used could 

 be arrived at. 



From the data afforded by these experiments, 

 M. Joannis appears to have conclusively shown 

 that the only stable compound is NaK.^, all others 

 being mixtures of this, with excess of one or other 

 of the two metals. It is very satisfactory that a 

 reliable method has at last been found of distin- 

 guishing between true compounds and physical 

 mixtures of metals, and rather remarkable that 

 one of the earlier analyses of the most stable com- 

 bination of sodium and potassium gave as the per- 

 centage of potassium 70.5, a number which closely 

 approximates to that required for NaKj. — Nature. 



SURFACE CONDENSATION OF GLASS. 

 Among the investigations on this point is that 

 of Bunsen. A bundle of glass threads, the total 

 surface of which was determined by preliminary 

 observations and calculations, was enclosed in a 

 chamber connected with a long tube, the lower end 

 of which was dipped in mercury. The gradual 

 rise of the mercurial column showed that an ap- 

 parent absorption of carbonic acid by the glass was 

 still going on at the end of three years. Later 

 observations proved that, although the glass had 

 been carefully dried, it is impossible to get rid of 

 all the adhering moisture, unless the temperature 

 is raised to a point not far short of the critical 

 temperature of water. If this precaution has been 

 omitted, carbonic acid, if present, will, according 

 to Bunsen, be dissolved in the water-film; and 

 since the inner layers of the liquid are subjected 

 by molecular attraction to a pressure which is 

 measured by hundreds of atmospheres, they are 

 capable of absorbing enormous quantities of the 



