Platinum principal characteristics

The principal characteristics of this method are the electrolysis of solutions of organic compounds using electrodes of platinum or graphite at anode potentials below those which could give rise to the evolution of elemental fluorine. 

Such are the principal properties of forged platinum, or of the metsl made into utensils, wire, or thin leaves but in its ether states, such as platinum black and spongy platmam, it exhibits other properties, which are highly interesting and characteristic of this metal. 

The other platinum metals form compounds which arc in general similar to those formed by platinum. Table XLIV gives in tabular form the principal compounds formed by the associated metals. In general their formation, characteristics, and properties will be suggested by comparison with tho corresponding platinum derivatives. The following characteristics are worthy of note-... 

With the exception of gold and the platinum-group metals (Ru, Rh, Pd, Os, Ir, and Pt), most metallic elements are found in nature in solid inorganic compounds called minerals. Table 23.1 lists the principal mineral sources of several common metals, three of which are shown in Figure 23.2 . Notice that minerals are identified by common names rather tlian by chemical names. Names of minerals are usually based on the locations where they were discovered, the person who discovered them, or some characteristic such as color. The name inalachite, for example, comes from the Greek word malache, the name of a type of tree whose leaves are the color of the mineral. 

For the international practical temperature scale the platinum thermometers serve as standard (interpolation) instruments with characteristics values such the reduced resistance, the temperature coefficient of the resistance and the platinum temperature. Interpolation polynomials of the third to fifth degrees, using as the principal reference points 0, 100 and 419.58 °C (fusion of Zn) are used most frequently (as a standard accessory of commercial products). Another form of resistance thermometers are films or otherwise deposited layers (0.01 to 0.1 pm thick). They can be suitably covered to protect against corrosive media and platinum deposited on ceramics can withstand temperatures up to 1850 K. Non-metals and semiconductor elements can be found useful at low temperatures. 

Even though there are a number of metals that appear suitable for resistance thermometry, platinum has come to occupy a predominant position, partly because of excellent characteristics, such as chemical inertness and ease of fabrication, and partly because of custom that is, certain desirable features such as ready availability in high purity and the existence of a large body of knowledge about its behavior have come into being as its use grew and have tended to perpetuate that use. Its sensitivity down to 20 K and its stability are excellent. Its principal disadvantages are low resistivity, insensitivity below about 10 K, and a variation of the form of the resistance-temperature relation from specimen to specimen below about 30 K. 

---