Polarographic Behaviour of the Hexa-ammine-chromium(III) Ion: Role of Hydrogen Ions
HEXA-AMMINECHROMIUM(III) ion in acetate buffer solutions is reduced at the dropping mercury electrode, and gives two polarographic waves. The first wave, which is well defined, is considered to be a one-electron reduction of Cr(III) to Cr(II)1. Its half-wave potential at 25° C was found to be −0.970 V versus saturated calomel electrode in 0.1 M acetate buffer solution which contained 0.9 M potassium chloride and 0.005 per cent gelatin (Fig. 1, curve a). The limiting current of this wave was diffusion-controlled and proportional to the concentration of the complex ion up to 5 mM. Both the half-wave potential and the diffusion current remained constant when the pH was varied from 4.5 to 5.45. No change was observed when potassium chloride was replaced by ammonium chloride at the constant ionic strength. The plot of log ī/(īd − ī) versus E, where ī means the average current, īd the average diffusion current, and E, the potential of the dropping mercury electrode, gave a straight line with a reciprocal slope of 64 mV, whereas the examinations with Kalousek's circuit and alternating current polarograph showed that this wave has nearly irreversible character.
Polarographic Behaviour of Chromium-Dipyridyl Complexes
IT has been shown previously that dipyridyl (dipy) complexes of cobalt and nickel are reduced at the dropping-mercury electrode with the formation of uni- and zero-valent complexes, respectively1,2. Further work led to the conclusion that iron(II)–dipyridyl complex is not reduced at the dropping mercury electrode and that the complex Mn(dipy)32+ is reduced with the formation of manganase(I) complex (unpublished results).
THE IRON-ACETOCARMINE METHOD OF FIXING AND STAINING CHROMOSOMES
A short description of this procedure was given in Vol. 55 of the American Naturalist, pp. 573â€”574. The method has now been used almost daily for five years, and certain improvements have suggested themselves. The solution can be prepared by mixing about equal volumes of glacial acetic acid and water. To this is added powdered carmine in excess. The liquid is then â€ ? just brought to boil, cooled, and decanted. To the red solution there are then added a few drops of a solution of ferric hydrate in 50 per cent. acetic acid, to act as a mordant. The amount of iron varies with different objects. Too much produces a precipitate in a short time. The more