6g8

DYEING AND CALICO PRINTING.

38°

= 0-825

n

0

c*

-tj-

0-804

39

o*8ig

43

0-799

40

0-814

44

0-794

41

0*809

diredt

scale of specific gravity assumes water to

be 1, or

heavier liquids requiring larger numbers, and all lighter ones numbers smallerthan unity. This scale shows at once the weight per gallon of any liquid,the two first figures to the left hand representing pounds avoirdupois, and thetwo or more following to the right being decimal fradtions of a pound. Thusif a sample of double muriate marks 1-450, a gallon of it weighs 14I lbs.

Twaddell’s scale makes water = 0, and the strongest oil of vitriol = 170°.Unlike diredt specific gravity, it extends only to liquids heavier than water.For greater accuracy the scale is arranged on a set of six instruments, num-bered progressively upwards. Thus a No. 1 Twaddell ranges from 0 to 32°.

The relation between Twaddell’s scale and diredt specific gravity is verysimple. To convert a degree of Twaddell into the corresponding degree ofdiredt specific gravity, multiply by 5 and add I'ooo to the produdt. Thus if ableaching-liquor marks 7° Tw., its specific gravity is 7

5

35

I'OOO

A sample of single aquafortis marks 33° Tw.

33

5

i'°35

Its specific gravity is then-

165

I'OOO

1-165

If the specific gravity has been taken the degree of Twaddell may be foundby reversing this rule, subtradting rooo, and dividing the remainder by 5.Thus a sample of double aquafortis marks specific gravity 1-350. Its degreeon Twaddell’s scale will be— .

1-350

I'OOO

5) 350

70° Tw.

In some hydrometers, graduated for diredt specific gravity, the first figureis omitted. On such water marks 0°, and the above-mentioned sample ofdouble aquafortis 350° A peculiar hydrometer—called the ammonia-glass orammonia-meter—is used in some distridts for the sale of ammonia. It rangesfrom io° (= water) to 45 0 , representing the lightest liquors. It very nearlyagrees with Baume’s light glass. Hydrometers give inaccurate results ifapplied to—■

a. Hot liquids.

b. Glutinous liquids, solutions of gum, starch, size, &c.

c. Effervescing liquids.

1 1 . Liquids holding solid matters in suspension.