Since proteins differ markedly in their solubilities at high ionic strength, salting-out is a very useful procedure to assist in the purification of a given protein. The commonly used salt is ammonium sulfate, as it is very water-soluble, forms two ions high in the Hofmeister series.It is generally used as a saturated aqueous solution which is diluted to the required concentration, expressed as a percentage concentration of the saturated solution (a 100% solution).his is usually done by adding solid ammonium sulfate, but calculating how much ammonium sulfate to add to a solution at one concentration to achieve a desired higher concentration is tricky, since addition of ammonium sulfate significantly increases the volume of the solution.
A phenocryst is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock. Such rocks that have a distinct difference in the size of the crystals are called porphyries, and the adjective porphyritic is used to describe them.
Phenocryst thumb|right|300px| Granites often have large feldspathic phenocrysts. This granite, from the Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through).