Subsequently these deposits were solidified through folding, pressure and heat into rock masses of varying stability ( cleavage takes place at 250? 400 �C, silicic acid, i . e . quartz, can be mobilised at 300 �C ).
32.
The paradox of the plankton results from the clash between the observed phylogenetic levels despite the limited range of resources ( e . g . light, nitrate, phosphate, silicic acid, iron ) for which they compete amongst themselves.
33.
It is considered archaic now, as the terms " acidic " and " basic rock " were based on an incorrect idea, dating from the 19th century, that silicic acid was the chief form of silicon occurring in rocks.
34.
In chemical terms, the pozzolanic reaction occurs between calcium hydroxide, also known as portlandite ( Ca ( OH ) 2 ), and silicic acid ( written as H 4 SiO 4 or as Si ( OH ) 4 ):
35.
The earth's crust and soils are dominated by the silicic acid in combination with Na, Al, K, Ca, Fe and O ions . . . . Those elements are components of primary minerals, whereas primary minerals are components of parent rocks.
36.
In order to prevent the formation of amorphous silica gels precipitating from supersaturated solutions without reacting with the aluminium or magnesium cations to form crystalline silicates, the silicic acid must be present in concentrations below the maximum solubility of amorphous silica.
37.
Silicon in the form of silicic acid, which usually appears as a neutral molecule in the pH range of most natural waters, may also be included for some purposes ( e . g ., when salinity / density relationships are being investigated ).
38.
While the specific composition and properties of the marl varied depending on what layer it was found in, blue marl was generally composed of 38.70 % silicic acid and sand, 30.67 % oxide of iron, 13.91 % magnesia, 1.14 % phosphoric acid, and . 31 % sulphuric acid.
39.
In the first place the silicic acid to be supplied to the growing crystal must be in a monomeric form, i . e ., silica should be present in very dilute solution ( Caill�re et al ., 1957; Caill�re and H�nin, 1962; Wey and Siffert, 1962; Millot, 1970 ).
40.
Abu Mansur distinguished between sodium carbonate and potassium carbonate, and seems to have had some knowledge about arsenious oxide, cupric oxide, silicic acid, and antimony; he knew the toxilogical effects of copper and lead compounds, the depilatory vertue of quicklime, the composition of plaster of Paris and its surgical use.
