Paper Hygrometers

Paper hygrometers are made by saturating white blotting paper with the following liquid and then hanging up to dry:

Cobalt chloride...... 1 ounce

Sodium chloride..... J ounce

Calcium chloride..... 75 grains

Acacia............. 1/2 ounce

Water.............. 3 ounces

The amount of moisture in the atmosphere is roughly indicated by the changing color of the papers, as follows:

Rose red.........   rain

Pale red.........   very moist

Bluish red........  moist

Lavender blue ....   nearly dry

Blue.............   very dry

Colored Hygroscopes

These instruments are often composed of a flower or a figure, of light muslin or paper, immersed in one of the following solutions:

I

Cobalt chloride. ... 1 part

Gelatin........... 10 parts

Water............ 100 parts

The normal coloring is pink; this color changes into violet in medium humid weather and into blue in very dry weather.

II

Cupric chloride. .. 1 part

Gelatin........... 10 parts

Water............ 100 parts

The color is yellow in dry weather.

III

Cobalt chloride.. .. 1 part

Gelatin........... 20 parts

Nickel oxide...... 75 parts

Cupric chloride... . 25 parts

Water............ 200 parts

The color is green in dry weather.