Crust is outer layer of the solid earth, above the Mohorovicic discontinuity. Its thickness averages about 35 km on the continents and about 7 km below the ocean floor, and has the approximate chemical composition:
Element | Percentage (%) |
---|---|
oxygen | 47 |
silicon | 28 |
aluminium | 8 |
iron | 4.5 |
calcium | 3.5 |
sodium | 2.5 |
potassium | 2.5 |
magnesium | 2.2 |
Hardness is the resistance of a material to deformation of an indenter of specific size and shape under a known load. This definition applies to all types of hardness scales except Mohs scale, which is a based on the concept of scratch hardness and is used chiefly for minerals. The most generally used hardness scales are Brinell (for cast iron), Rockwell (for sheet metal and heat-treated steel), Knoop (for metals).
Mohs’ scale of mineral hardness characterises the scratch resistance of various minerals through the ability of a harder material to scratch a softer. It was created by the German mineralogist Friedrich Mohs (1773-1839). Mohs based the scale on the ten readily available minerals.
Hardness | Mineral |
---|---|
1 | talc (Mg3Si4O10(OH)2) |
2 | gypsum (CaSO4·2H2O) |
3 | calcite (CaCO3) |
4 | fluorite (CaF2) |
5 | apatite (Ca5(PO4)3(OH-,Cl-,F-)) |
6 | orthoclase feldspar (KAlSi3O8) |
7 | quartz (SiO2) |
8 | topaz (Al2SiO4(OH-,F-)2) |
9 | corundum (Al2O2) |
10 | diamond (C) |
Three way safety bulb (pipette filler bulb) is used for pipeting. The attachment is placed over the mouth of the pipet. Squeeze the air valve (A) and the bulb simultaneously to empty the bulb of air. Place the tip of the pipet below the solution's surface in the beaker. Gradually squeeze the suction valve (S) to draw liquid into the pipet. If the level of the solution is not high enough, squeeze the air valve (A) and the bulb again to expel the air from the bulb. Draw up more liquid by squeezing the suction valve (S). When the liquid is above the specified volume, stop squeezing the suction valve (S). Do not remove the bulb from the pipet. Do not allow liquid to enter the pipet bulb.
Generalic, Eni. "Mohr pipette." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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Periodic Table