Hydrogen absorption into platinum

Fig. 30. Change of the IR reflection absorption spectrum of the linearly adsorbed CO on a platinum electrode with potential (a) in the hydrogen region between 0.5 and 0.35 V (NHE) and (b) across the hydrogen region into the double layer region. Curve 1, 0.15 V (NHE) curve 2, 0.30 V (NHE) curve 3, 0.35 V (NHE) curve 4, 0.40 V (NHE) curve 5, 0.425 V (NHE) curve 6, 0.450V (NHE) curve 7, 0.475V (NHE) curve 8, 0.50 V (NHE).

After PtO decomposes into platinum hydroxide and platinum, hydrogen absorption appears between approximately +0.2 V and —0.25 V (versus SCE) ... 

Magnanini studied the absorption spectrum and A. Speransky found that the electrical conductivity of aq. soln. shows that only a small proportion of the salt is ionized. The soln. of the violet modification conducts electricity three times better than that of the green. G. Gore electrolyzed a cone. soln. of chromic fluoride acidified with hydrofluoric and hydrochloric acids, and found that the liquid became hot no gas was liberated at the cathode, but chlorine and ozone were liberated at the platinum anode which was not corroded. C. Poulenc showed that the salt is reduced by hydrogen at dull redness. The heat of formation is 230-95 Cals, per mol—vide infra, the dichloride. Steam transforms chromic fluoride into chromic oxide. Chromic fluoride is insoluble in water, and alcohol hydrogen chloride transforms it into chromic chloride hot hydrochloric, sulphuric, and nitric acids attack chromic fluoride only a little hydrogen sulphide converts it into black sulphide and molten alkali nitrate or carbonate converts it into chromate. A. Costachescu prepared complex pyridine salts. 

The sampling-boat technique is frequently hampered by poor precision. Delves (D5) described an improved system. He modified the system of White (W5) who used a platinum-wire loop in conjunction with an absorption tube to increase sensitivity. Delves vaporized samples from microcrucibles made of nickel foil into a nickel absorption tube situated in air-acetylene flame. The sensitivity is 1 X g lead per 1% absorption at the 2833 A line. Only 10 /lil of whole blood are required. Before analysis, the sample is dried in the nickel crucible on a hot plate at 140°C (ca. 30 seconds) and then is partially oxidized with 20 jal of 30% hydrogen peroxide at 140°C until a dry yellow residue is obtained. Standards of lead added to normal blood are run in a similar fashion. 

The ease of reduction of an alkene decreases with the degree of substitution of the double bond, and this sometimes allows selective reduction of one double bond in a molecule which contains several. For example, limonene 7 can be converted into p-menthene (by reduction of the terminal alkene) in almost quantitative yield by hydrogenation over platinum oxide if the reaction is stopped after absorption of one molar equivalent of hydrogen. In contrast, the isomeric diene 8, in which both double bonds are disubstituted, gives only the completely reduced product (7.7). 

---