In order to change degrees Twaddell into specific gravity, multiply by 5, add 1,000 and divide by 1,000.

Example: Change 168 deg. Twaddell into specific gravity.

168 X 5

840 1,000

1,000)1,840

1.84, specific gravity.

To change specific gravity into degrees Twaddell, multiply by 1,000, subtract 1,000 and divide by 5.

Example: Change 1.84 specific gravity to degrees Twaddell.

1.84 X 1,000

1,840

1,000

5)840 168° Tw.

Specific Gravity

Determination of Specific Gravity: Solids: (1) Solids heavier than, and insoluble in water: a. By weighing in air and water. -

Sp. gr. =

(weight in air)

(loss of weight in water)

6. By Nicholson's hydrometer. Let w1 be the weight required to sink the instrument to the mark on the stem; to take the specific gravity of any solid substance, place a portion of it weighing less than w1 in the upper pan, with such additional weight, say w3, as will cause the instrument to sink to the zero mark. The weight of the substance is then w1 - w3. Next transfer the substance to the lower pan, and again adjust with weight w4 to the zero mark.

Sp. gr. =

W1 - W3

W4 - W3

c. By the specific gravity bottle (applicable to powders). Weigh the flask filled to the mark with water, then place the substance, of known weight, in the flask, fill to the mark with water, and weigh again.

Sp. gr. =

weight of substance in air

wt. in air + wt. of flask and water wt. of flask filled with substance and water.

(2) Solids lighter than and insoluble in water. The solid is weighed by a piece of lead and weighed in water.

Sp. gr. =

(weight of substance in air)

(wt. of lead in water) - (wt. of lead and substance in water) + (wt. of substance in air)

(3) Solids heavier than and soluble in water. Proceed as in 1 a, using instead of water some liquid without action on the solid.

(weight of bulk of liquid equal to substance) = (weight of substance in air) - (weight of substance in liquid).

(wt. of bulk of water equal to substance) =

(wt. of bulk of liquid equal to substance)

(sp. gr. of liquid)

Sp. gr. =

(weight of substance in air)

(weight of bulk of water equal to substance)

Liquids: (1) By the hydrometer.

(2) By the specific gravity bottle.

Weigh the bottle filled to the mark with water, and again when filled to the mark with liquid.

Sp. gr.=

(weight of liquid and bottle) - (weight of bottle)

(weight of water and bottle) - (weight of bottle)

Tables of Specific Gravity will be found under Weights and Measures.