672 THE POPULAR SCIENCE MONTHLY. 



What most strikes one is the invariably greater hygroscopic 

 power of wool than of linen; the maxima and minima of flannel and 

 linen being respectively 175 and 111, 75 and 41. 



Observations 5 to 8 show that linen changes the quantity of its hy- 

 groscopic water at a proportionately quicker rate than flannel. The 

 two pieces were for twelve hours in the cellar, when linen absorbed 

 111, flannel 175; immediately after, for four hours, in a cold place, 

 where linen lost 18 per 1,000 of its absolutely smaller amount of 

 water, while the flannel lost only 15 per 1,000; but during the next 

 three hours linen lost only 2, but flannel 12 per 1,000. 



When (Obss. 9 to 15) the pieces had come from the cold lecture- 

 room into a warmed room, linen again ceased giving off water at a 

 much quicker rate than flannel. 



The accelerated rate, only in an opposite direction, took place 

 again (Obss. 15 to 18) when the temperature in the room sunk from 

 65 to 59. 



All bodies become more hygroscopic with a sinking temperature, 

 but the absorption of water and increase of weight, as well as the 

 contrary process, take place proportionately quicker with linen than 

 with flannel. 



The more the air in any material is displaced by water, the less it 

 keeps us warm, the quicker it conducts the heat ; hence the frequent 

 injury resulting from wet clothes, and the striking discomfort pro- 

 duced by a damp cold. You all know how comfortable we can feel 

 in a walk, when the air is cold and dry, and how differently we feel 

 when it is damp, although not colder. Then our clothes also get 

 much damper, and conduct more of our heat away. 



This is not to be underrated. We have seen in the table that 

 1,000 parts of flannel took up in the cellar 157 parts of water. Take 

 the weight of a whole woolen clothing as ten pounds, and you see 

 that it may absorb one and a half pound of hygroscopic water, 

 which requires about 1,680 caloric units from our body to be evap- 

 orated. 



Linen and flannel bear the same relation toward water they are 

 wetted with as toward their hygroscopic water. Linen is quickly 

 wetted and soaked, wool more slowly, but linen cannot take up the 

 same quantity. Spilled water has certainly taught you this many 

 times, when you wanted to take it up. It is the same in evaporation, 

 which is also much quicker from linen. Two equal pieces of linen 

 and flannel, weighing each 1,000 grammes, put into water and wrung 

 out till they no longer yield a drop of water, keep back respectively 

 740 and 913 per 1,000. 



But a much greater difference exists in the intensity of evapora- 

 tion from wet linen and from wet flannel, during equal periods, in a 

 heated room. 



