Page:Popular Science Monthly Volume 10.djvu/693

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673
RELATIONS OF THE AIR TO OUR CLOTHING.
OBSERVATIONS. TEMPERATURE. MINUTES. WATER TO 1,000 GRAMMES OF
Linen. Flannel.
1 70° Fahr. · · 740 913
2 68 15 521 701
3 68 30 380 603
4 67 30 229 457
5 66 30 99 309
6 66 30 55 194
 

It is easy to see from this table how much quicker linen works than wool in every direction.

During the first 75 minutes there evaporated from 1,000 parts of linen 511, from 1,000 parts of flannel 456 water; afterward the reverse took place: in the following 30 minutes 130 evaporated from linen, 148 from flannel, and in the last 30 minutes only 44 per 1,000 from linen, but 115 from flannel.

It is also evident how much more evenly the drying proceeds in wool: in the first 15 of the whole 135 minutes 219 evaporated from linen, in the last 15 minutes 28 per 1,000, while with wool it was respectively 212 and 97 per 1,000. I must not forget to mention that all these experiments were made with pieces of nearly equal size and shape.

It is self-evident that all textures lose their permeability to the air in proportion to their state of humidity, the water partly at least obstructing the pores. Coarser stuffs with larger pores will keep their permeability longer; if the pores are equal, the difference in the adhesion of the water to the substances will come into play. Linen, cotton, and silk are very different in this respect from sheep's-wool. The former become very quickly air-tight by wetting, the latter scarcely so, or only after a longer soaking. Soldiers can tell how damp and vaporous the air becomes under a wet tent, and how quickly the tent becomes airy when it begins to dry.

As the porosity of all fabrics depends chiefly on the elasticity of the fibres of their material, it must be of great importance how far that elasticity keeps under wet and dry. There, again, wool stands apart; its fibres do not lose much elasticity when they get wet: it is not so with other fibres. Wet linen and silk are just like Krieger's shorn fur, when it was coated with varnish or gum-arabic. The greater facility of catching cold in wet linen or silk than in wet wool is in exact proportion to the greater facility with which water expels the air contained in their fibres. Many of you may have learned a lesson from a wet linen or cotton and a wet woolen sock.

On the other hand, there is an advantage in these materials if we want to keep ourselves cool and dry. By means of them we part with heat and moisture from our surface much quicker, and hand them over to other layers for further removal.

To be quite methodical I ought now to treat of the different parts