Blue potassium chromate

The series is prepared by treating blue potassium chromi-oxalate, [Cr(C204)3]Ks, with aqueous 10 per cent, ethylenediamine until a red salt begins to separate from the dark violet solution. On cooling the mixture the double salt, oxalato-diethylenediamino-ehromium dioxalato-ethylenediamino-chromate, [Cr en2C204][Cr en(C204)2], is obtained in... 

Pigments consisting of zinc potassium chromates combined with blue pigments are no longer of importance. 

If an excess of hydrogen peroxide be added to a solution containing a chromate, made slightly acid with sulphuric acid, and the mixture then shaken up with a few c.c. of ether, a blue ethereal layer is formed above the aqueous solution. The colour is due to the formation of perehromie acid (see p. 73), and the reaction aSords a usefiil test for identifying chromates in presence of sulphuric acid. If the ether used is free from alcohol, 1 part of potassium chromate in 40,000 parts of water can be detected. Another sensitive test for chromates and di-ehromates is to add a trace of a-naphthylamine to the solution and acidify with tartaric acid, when an intense blue colour results. ... 

Aqueous solutions of some compounds that contain chromium. (Left to right) Chromium(II) chloride (CrCl2) is blue chromium(III) chloride (CrClj) is green potassium chromate (K2Cr04) is yellow potassium dichromate (K2Ct207) is orange. 

Beyond wave-length 5450 the coeff. becomes practically zero in very dil. soln., the coeff. for wave-length 5180 is about 0-000013. The values are the same for the acid as for the salts, for solid potassium dichromate as for its soln., for the ammonium salt as for the potassium salt, and it follows that the absorption exerted by sohd or dissolved alkaline dichromates is sensibly identical with that of the chromic acid which they contain. With soln. of potassium chromate, the absorption is in the blue and the violet, and with dilution, the absorption extends more in the direction of the red. Thus, 0. Knoblauch found that in cone, soln., the absorption begins at 4900, and in dil. soln., at 5100. W. Bohlendorff obtained similar results while J. M. Hiebendaal observed that the absorption begins at 5050, and in dil. soln. at 4770. K. Vierordt, P. Pogany, F. Griinbaum, A. Hantzsoh, P. Bovis,... 

Bersch (1901) gives a recipe for chrome blue according to Gamier, whereby a mixture of 48.62 parts potassium chromate, 65 parts fluorspar and 157 parts of silica are fused in a crucible lined with coal dust. The extent of use of this pigment is unknown. 

To 3 ml. of the solution add about 5 ml. of concentrated nitric acid and 5 drops of 5 per cent, potassium chromate. Mix well. A blue colour develops in about a minute if sugar be present. 

Colour Test.—An aqueous solution of glycerol gives a blue colour on addition of a few drops of 5 per cent, potassium chromate and excess of nitric acid, showing the presence of the primary and secondary alcohol groups (p. 109). 

Potassium periodate - tetrabase test A solution of the tetrabase (tetra-methyl-diamono-diphenylmethane) in chloroform is employed as a sensitive test to identify very small amounts of manganese as permanganic acid. The latter oxidizes the tetrabase to an intensely blue compound. Chromium salts should be absent for they are oxidized by periodates to chromates, which yield a similar colour with the tetrabase . 

The qualitative detection of thallium is easily achieved by emission spectroscopy, thallium giving a green flame color. Thallium(I) iodide is a yellow precipitate that is insoluble in water, nonoxidizing acids, ammonia, and potassium cyanide, but that can be dissolved in sodium thiosulfate. Traces of thallium can be detected by dyes such as Brilliant Blue or Rhodamine B. Tl (or Tl after reduction by SO2) can be determined by BrOs" or titrant. A gravimetric method uses Tl chromate. ... 

Potassium tris(malonato)chromate(IlI) trihydrate is a blue-green compound which is very soluble in water. The cis isomer of potassium diaquabis(malo-nato)chromate(III) trihydrate is purple and also very soluble in water. The trans isomer is violet and fairly soluble in water, but it is more soluble than the analogous oxalate compound. All three compounds exhibit two absorption maxima in their visible absorption spectra, listed in Table I. 

Cold H,SO, does not color it alone on addition of potassium di-chromate, a fine blue color is produced, which, on dilution wilk uxUert passes to violet, and, if not dilutei.1, to black. 

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