Typically roomtemperature distilled water is used.  It is best to use water that isboiled, because deionized water that has been sitting for a time to degas waterand lessen the chance of fine air bubbles.  A tiny drop of wetting agent,alcohol, or dishwashing liquid maybe added to the water to decrease surfacetension of water which can adversely affect the results. One drop of detergent liquid the size of a pin head destroys surfacetension in 1 liter of water.
通常使用室温蒸馏水。最好是利用煮沸的水，因为去离子水已经静待一段时间脱气和减轻产生细微气泡的机会。加入一些润湿剂，酒精，或洗碗液于水可降低水的表面张力，它可以产生对结果不利的影响。一滴针头大小的液体洗涤剂可以破坏一公升水的表面张力。

SPECIFICGRAVITY

Gem materials vary greatly in density -- ambermay float in salt water (density near that of water), while hematite is morethan five times the density of water. This is why two different gemstones may havethe same size but different weights and vice versa-- a one carat roundbrilliant diamond of typical proportions will be approximately 6.5 mm in diameter, while a round brilliantruby of the same size (6.5 mmin diameter) and proportions will weigh approximately 1.55 carats.

宝石材料的密度差别很大-琥珀可以在海水中漂浮（密度接近于水的密度），而赤铁矿是超过5倍水的密度。这就是为什么两个不同的宝石，可能有相同的大小，但不同的重量，反之亦然。一个典型的克拉圆形灿烂钻石的比例将约为直径6.5毫米，而同样大小直径和比例（6.5毫米）的圆形红宝石将重约1.55克拉。

Generally, gemologists refer to specificgravity, or relative density -- the ratio of the density of a gemstone relativeto that of water. The specific gravity(SG) of a gem is an indication of its density. It is calculated by comparingthe stone's weight with the weight of an equal volume of water.

一般来说，宝石指比重，或相对密度-宝石的密度相对于水的密度。宝石的比重会（SG）指标示其密度。计算方法是通过比较宝石的重量和同等体积水的重量。

The greater a stone's specific gravity, theheavier it will feel. For example, a small cube of pyrite, with an SG of 5.2,will feel heavier than a larger piece of fluorite with an SG of 3.18; and aruby (SG 4.00) will feel heavier than an emerald (SG 2.71) of similar size.

宝石的比重越大，它会觉得更重。例如，一个小立方体黄铁矿比重是5.2，会感到比更大的萤石比重是3.18重;和红宝石（比重4.00）会觉得同样大小的比绿宝石（比重2.71）重。

Specific Gravity

From The Gemology Project

You can contribute to thistopic through the submission page.

通过此页面，您可以有助于了解这一主题。

Thespecific gravity (SG) of gemstones is a constant widely used in gemologicalproperty charts. Although not every gemologist enjoys doing an SG test, it isstill a property which can be very useful when other general tests fail.

宝石的比重（SG）不断被广泛使用在宝石特性图表。尽管并非所有宝石家喜欢做比重的测试，但它仍然是一个特性，当其它一般性测试失败时，它是可以非常有用的。
The method of determination uses a hydrostatic balance.

Specificgravity (also known as "relative density") is the ratio between theweight of a stone in air and the weight of an equal volume in water. Byconvention, the temperature of the water is 4° C and at standard atmospherebecause the density of water is greatest under these conditions. Roomtemperature conditions are adequate for gemological purposes, as the smalldifference in density of the water will have little effect on the readings(measured to the second decimal).

测定方法采用静水力平衡法

比重（也称为“相对密度”）是一个宝石在空气中重量和在同等体积水的重量之间的比例。按照惯例，水的温度为4℃和标准大气压，因为水的密度是在这种情况下最大。测试宝石室温条件是足够的，对水的密度而言会有小的差异，但对读数而言影响不大（测量至小数二位）。

Sincespecific gravity is relative to the weight of an object in air and its weightin water, it is a ratio and isn't expressed in units (such as kg/m³). Forinstance, the SG of Diamond = 3.52 (whereas the density of Diamond = 3.52 g/cm³). In gemology, specific gravityis, usually, determined through an apparatus based on Archimedes' Principle.Archimedes' Principle (or the Law of Buoyancy) states that: the upward force onan immersed object is equal to the weight of the displaced fluid.
This maysound complicated but it is a fairly simple, yet brilliant, law.

由于比重是相对于对象在空气中的重量和它在水中的重量，这是一个比例，并不表示单位。例如，钻石的比重= 3.52（而钻石的密度= 3.52克/厘米³）。宝石而言，比重通常是通过以阿基米得原理为基础的测试设备。
阿基米得原理（或浮力法）指出：在一个对沉浸对象向上的力等于置换液体的重量。
这可能听起来复杂，但它是一个相当简单定律。

Considertwo balls of equal weight but of different specific gravity, for instance a 10gram gold ball and a 10 gram silver ball. The gold ball has a sg of 19.3, whilesilver has a sg of 10.5. Because gold has a sg that is almost twice as muchas silver, you can imagine that the 10 gram gold ball will be smaller than the10 gram silver ball. In other words, the gold ball will have a smaller volumethan the silver ball. When you hang both balls in water (immersed), then thesilver ball will displace much more water than the golden ball due to itshigher volume.

考虑两个相等重量的球，但比重不同，例如一个10克的黄金球和10克银球。黄金球的比重有19.3，白银的比重有10.5。
由于黄金SG，几乎是银的两倍，你可以想象，10克黄金球会比10克银球小。换句话说，黄金球会比银球体积小。
当你挂在两个球浸泡于水中，然后银球将比黄金球置换较高量甚至更多的水。

Waterhas a sg of 1, so the weight of a cubic centimeter of water is 1 gram (actually0.0098 Newton,but grams used for simplicity). Through some simple math we can calulate thevolume of the balls. The volume of the gold ball is 0.52 cubic centimeter andthe volume of the silver ball is 0.95 cubic centimeter (volume is mass dividedby density).
From thiswe can conclude that the silver ball will displace 0.95 cubic centimeter ofwater, which weighs 0.95 gram. The golden ball will displace 0.52 grams ofwater (because 1 cubic centimeter of water weighs 1 gram).

水的SG是1，所以1立方厘米水的重量为1克（实际上0.0098牛顿，但为简单使用克）。通过一些简单的数学，我们可以计算出球的体积。黄金球的体积是0.52立方厘米和银球的体积是0.95立方厘米（体积是质量/密度）。
由此我们可以得出结论，银球将置换0.95立方厘米的水，重量0.95克。金球将置换0.52克的水（因为1立方厘米的水重1克）。

Nowback to Archimedes' Principle: the upward force on an immersed object is equalto the weight of the displaced fluid (the fluid being water in this case). Thesilver ball displaces a higher weight of water, so it will experience a largerupward force than the golden ball and will rise higher in the water whenimmersed.

Acommon mistake is to drop the object in the water in a way that it will sink tothe bottom. It can not work in that case as it is then no longer"immersed".

现在回到阿基米得的原理：对某一沉浸对象向上的力等于置换液体的重量。银球置换较高的水，因此它体验一个向上的力大于金球，并上升在水中浸泡高度。一个常见的错误的方式，是放对象在水中让它沉到水底。在这种情况下，它不能工作，因为那不是“浸泡”。

[edit]

Density

Densityis different from specific gravity in that it is the mass of an object dividedby its volume, expressed in kg/m³ by SI (Le Système International d'Unités -The International System of Units) standards. In gemology, g/cm³ is used. Otherweighing systems are still widely in use (mostly in the USA and the UK), but the metric system of theSI is slowly finding its way there as well.

密度是不同的比重，它是由一个物体的质量除以它的体积，以千克/立方米表示的SI标准。在宝石，使用克/厘米³。其它称重系统仍然广泛使用（主要在美国和英国），而是SI公制系统慢慢发现其方式也有。

Mass and weight

Massis the amount of material in an object and is a physical property of thatobject (like a gemstone), expressed in kg (kilogram) by SI standards.

Weightis the gravitational force (9.8 m/s²)on that object and is expressed in N (newton). Weight is not a physicalproperty as it may change under different situations. A stone would weigh lesson Earth's moon than on Earth, but its mass would remain the same.

Ascan be concluded, we should use "mass" instead of "weight"when being scientifically correct, but in daily use mass and weight areinterchangeable.

Thecarat (ct) is an accepted unit of mass (or weight, if you please).

Measurement of specific gravity

Themethod of measuring SG is with a hydrostatic balance.
First,the stone is weighed in air and then weighed when fully immersed in water.After this, the weights are inserted into a simple formula.