what are the 2 varieties of hardness?
367986
The two hardnesses you are looking for must be scratch and indentation hardness.\n\nScratch hardness is caracterized by the Mohs scale (as commented before).\n\nIndentation hardness is caracterized by serveral scales, the most popular (here, in colombia) are the Rockwell hardness test and the Shore durometer.\n\nThe wikipedia link has in itself references to detailded information about many hardness scales that you may find useful
526901
Well, there are two types of hardness I know in chemistry. I don't know which of the two you are referring to so I'll just list both. \n\nThe first one is called "carbonate hardness", commonly known as alkalinity. It is the meaure of the ability of a solution to neutralize acid without changing the pH. It both controls and maintains water pH, and it is measured in degrees (dKH), parts per million of calcium carbonate (ppm CaCo3), or milliequivalents per liter (meq/L).\n\nThen, in contrast to carbonate hardness, there is general hardness which is the measurement of the total dissolved minerals in a solution. Test kits for general hardness measure the amount of calcium and magnesium salts present, and the result is expressed in degrees dH or dGH.
488410
You can describe different types:\n\nhttp://www.aecom.yu.edu/ehs/Industrial%20Hygiene/Fs_Fibergls.htm\n\nhttp://www.clarkcraft.com/fiberglasscovering.php3
403489
Go to azom.com they have info on both 304, 316 and many other metals.\n\nIn a nut shell, 316 stainless steels are more corrosion resistant than 304 stainless steels
745309
I think zero is the best, they have alot of concave. Any questions email me.
749219
a) Ag2S\nb) SnCl4\nc) Na3N\nd) SrI2\n\nDo us a favor and pay attention during class. That way you'd know how to do these.
1135022
The #1 pencil will always remain a free pencil no matter how hard it is or where you picked it up, right?  BTW, the hardness of a pencil is produced by mixing the correct amount of clay with the soft graphite before baking it.  I have had many pencils with clay inclusions that have torn the papers I was writing on.  Never happened in the good old days (before my time!) when they used real lead to write with.  In drafting class many considered #2 pencil lead as too soft but most considered 2H lead as "too hard" rather than "2 Hard" go figure.  Philosophers will likely tell you that life is a pencil.  To succeed you must get the lead out.  Good luck!
168232
ALways by sight at first. The most important properties are visual. Eg: colour, roughness, presence of any strange um 'flecks'..... or 'veins'. And then next, scratch something with it and put it into "moe's scale of hardness"
726893
Cubic zirconia is much harder than glass. Cubic zirconia about 8.5 on Moe's scale and glass about 5.
621098
PRESENCE OF BICARBONATES OF CALCIUM & MAGNESIUM CAUSE TEMPORARY HARDNESSWHICH CAN BE REMOVED BY BOILING,CLARKESMETHOD\nPRESENCE  OF CHLORIDES &SULPHATES OF CALCIUM&MAGNESIUM CAUSE PERMANENT HARDNESS WHICH CAN BE REMOVED BY GAN'S PERMUTITS METHOD,CALGON PROCESS.
890118
in the simplest terms, there are two major families of ceramics -- oxides and carbides.  \n\nIf you mean strongest (rather than hardest), a number of the oxides can form strong structures.  Bricks made of kaolin clay are are reasonable example.\n\nBut, if you mean, hardest, you should consider some of the carbides -- like silicon carbide or tungsten carbide.  These are so hard and tough that they are used to cut other ceramics (like the brick we just mentioned).
198982
hardness, luster, clevage, composition, crystal structure\n\niron is useful also in the mineral gypsum they use it to make drywall\n\nmost gems are valueable because they form extremely slow making them rare, they are also the very hardest type of mineral
845030
for minerals it's definitively the mohs scale. Talc = 2 Quartz = 8\nBut for some other substances such as Rubber or elastomer you could choose the Rockwell hardness (A or B), which is provided with a dart measurement.\nSo your question has to be more precise.
358269
HARD HOUSE-because its fast and hard. :)
477021
Not an element; yes its still the king of hardness\nThere are experiments ongoing with low-speed nuclear bombardment of iridium with smaller nuclei which are producing very thin layers of great density that approaches the hardness of diamond.
396032
Firstly, pencil lead IS graphite.  O.k, back to your question.  Both graphite and diamond are allotropic forms of carbon- they differ in the spatial arrangement of their molecules a lattice.  In diamond, the carbon atoms are arranged in a regular tetrahedral spatial arrangement, while in graphite, the carbons are arranged in an irregular "stacked" manner.  This structural difference results in different properties of hardness.  Diamond is the hardest substance known, with a Moh's scale reading of 10, while graphite is very soft and has a rating of approximately 1.
266027
Hard Water:\nWater containing soluble salts of calcium and magnesium and sometimes iron.\n\nSoft Water:\nWater having a low concentration of calcium and magnesium ions. According to US Geological Survey guidelines, soft water is water having a hardness of 60 milligrams per liter or less.