447 
in the laboratory. However, quantitative bleaching experiments allow 
of considerable accuracy and should afford fairly reliable data for com- 
parative purposes under practical conditions. 
Bleaching powder (chloride of lime) is used almost to the exclusion 
of all other agents, so that it alone need be considered. This chemical 
is usually applied in the form of a clear solution of approximately 5° Bé. 
strength (specific gravity, 1.036), made by disintegrating the powder 
in water and clearing it by allowing it to settle or by filtering. The 
amount of bleaching powder necessary to produce the required shade 
depends on several factors, chief among which is the completeness of the 
previous treatment—that is, the removal of the noncellulose.!? The kind 
of fiber to be bleached also materially affects the amount of bleaching 
agent required. It is the practice to base all calculations as to quantity 
upon the amount of bleaching powder required to bleach. 45.4 ' kilos of 
the original fiber. The quantities in general use for this weight of 
different fibers are stated as follows: 
Kilos.!4 
Rags (cotton and linen fiber) 0.907- 2. 268 
Straw 3. 175- 4.58 
Esparto 4.53 — 6.80 
Wood 5.44 -11. 34 
Jute and Manila 4.53 - 9.07 
The pulp is bleached either in the beating machine or in large chests 
termed “plotchers.” The exact procedure varies in the different mills, 
but time-saving devices and schemes are quite generally employed—that 
is, acid is added to hasten the bleaching action and artificial heat is 
supplied for the same reason. The following details of procedure, 
adopted for quantitative bleach experiments on abaca, apply as well to 
all the other fibers studied. It will be noted that all digestion experi- 
ments were performed on 1-kilo lots of raw material. This furnished 
in most instances about 450 grams of pulp. The washed, dry residues 
were repulped by beating or shaking with a definite volume of water, and 
a clear solution of bleaching powder of known strength was added, shghtly 
in excess of the amount required to produce a good white. In some 
instances the operation was performed in a model beating engine of the 
Hollander type of about one-half kilo capacity, but most of the bleaching 
"A well-boiled pulp should contain 90 to 95 per cent of cellulose—that. is, 
will lose from 5 to 10 per cent in weight in the process of bleaching. Cross and 
Bevan: Text-book on Paper Making, 160. 
* 100 pounds. 
14 2— 5 pounds. 
7-10 pounds. 
10-15 pounds. 
12-25 pounds. 
10-20 pounds. 
