other like scales, which makes the surface of the fiber rough; this
condition, together with the inclination of curling, renders it
capable of felting readily. Pure wool consists of a horny substance,
containing both nitrogen and sulphur, and dissolves in a potash
solution. In a clean condition, the wool contains from 0.3 to 0.5 per
cent. of ash. It is very hygroscopical, and under ordinary
circumstances it contains from 13 to 16 per cent. humidity, in dry air
from 7 to 11 per cent., which can be entirely expelled at a
temperature of from 226 to 230 degrees Fahrenheit. Wool when ignited
does not burn with a bright flame, as vegetable fiber does, but
consumes with a feeble smouldering glow, soon extinguishes, spreading
a disagreeable pungent vapor, as of burning horn. By placing a test
tube with a solution of five parts caustic potash in 100 parts water,
a mixture of vegetable fibers and wool fibers, the latter dissolve if
the fluid is brought to boiling above an alcohol flame, while the
cotton and linen fibers remain intact.

The solubility of the woolen fibers in potash lye is a ready means of
ascertaining the percentage of wool fiber in the paper. An exhaustive
analysis of the latter can be performed in the following manner: A
known quantity of the paper is slowly dried in a drying apparatus at
temperature of 230° Fahrenheit, until a sample weighed on a scale
remains constant. The loss of weight indicates the degree of humidity.
To determine the ash percentage, the sample is placed in a platinum
crucible, and held over a lamp until all the organic matter is burned
out and the ash has assumed a light color. The cold ash is then
moistened with a carbonate of ammonia solution, and the crucible again
exposed until it is dark red; the weight of the ash is then taken. To
determine the percentage of wool, a sample of the paper is dried at
230° Fahrenheit and weighed, boiled in a porcelain dish in potash lye