Alcohol Facts by National Draeger
EXHIBIT B-8
DENSITY
The mass of a unit volume of a material is called its density. Density may be expressed in terms of any consistent units of mass and volume as, for example, pounds per gallon, pounds per cubic foot, grams per cubic centimeter, or grams per milliliter. The most generally used unit is grams per milliliter.
In general, an increase in temperature or a decrease in pressure results in a decrease in density. These effects are large for gases so that both the temperature and the pressure must be taken into account. The effect of moderate changes in pressure on the density of liquids or solids may be ignored, but the effect of temperature must always be taken into account,.
SPECIFIC GRAVITY
Specific gravity is the ratio between the density of a body and the density of some substance assumed as a standard. For liquids and solids the standard is distilled water at 4 C, the temperature at which water reaches its maximum density.
Blood, which is heavier than water, has - for normal blood - a specific gravity of 1.055 at 20 C. Alcohol, which is lighter than water, has a specific gravity of 0.79 at 20 C. (In nonscientific work, 0.8 is often used.)
Since density can change with changes in temperature and pressure, as noted above, it is necessary to state these for complete accuracy. The standard pressure used is 760 mm. of mercury (29.92 inches barometric pressure), the average atmospheric pressure at sea level. In most cases the pressure makes so little difference that it is disregarded. Temperature is constant at 4 C, and the ratio is stated differently as the temperature of the substance being compared is charged.
