The remaining and less typical subordinal groups - sometimes ranked as orders by themselves - include among living animals the Proboscidea, cr elephants, and the Hyracoidea, or hyraxes, and among extinct groups the Amblypoda, Ancylopoda, Barypoda, Condylarthra, Litopterna and Toxodontia.
In any region of velocity where it is possible to represent p with sufficient accuracy by an empirical formula composed of a single power of v, say v m, the integration can be effected which replaces the summation in (to), (16), and (24); and from an analysis of the Krupp experiments Colonel Zabudski found the most appropriate index m in a region of velocity as given in the following table, and the corresponding value of gp, denoted by f (v)or v m lk or its equivalent Cr, where r is the retardation.
The element is not found in the free state in nature, nor to any large extent in combination, occurring chiefly as chrome-ironstone, Cr 2 O 3 FeO, and occasionally being found as crocoisite, PbCrO 4, chrome-ochre, Cr 2 0 3, and chromegarnet, CaO Cr 2 O 3.3SiO 2, while it is also the cause of the colour in serpentine, chrome-mica and the emerald.
The sesquioxide, Cr 2 0 3, occurs native, and can be artificially obtained in several different ways, e.g., by igniting the corresponding hydroxide, or chromium trioxide, or ammonium bichromate, or by passing the vapours of chromium oxychloride through a red-hot tube, or by ignition of mercurous chromate.
Other hydrated oxides such as Cr 2 0 3.2H 2 0 have also been described.
