12 
BULLETIN 309. U. S. DEPARTMENT OF AGRICULTURE. 
grinding; the sulphite process, by acid hydrolysis; the caustic-soda 
process, by hydrolysis with caustic soda; and the sulphate process, 
by hydrolysis with sodium hydrate and sulphid. 
From previous general knowledge of the paper value of fibrous 
plants and from the similarity of zacaton to known species, it was 
decided to investigate this material by the soda process, which con- 
sists in subjecting the material to the action of a caustic-soda solution 
at moderately high temperature for a definite length of time, which 
operation is technically known as cooking. Since the soda solutions 
at the temperatures required exert a steam pressure of 50 to 100 
pounds to the square inch, the cooking is effected in large, strong 
steel cylinders, known as digesters, which are of two general types, 
the upright stationary and the horizontal rotating. The prehminary 
cooking of zacaton was conducted in an autoclave, simulating the 
conditions of the upright stationary digester. The autoclave was 
of the regular laboratory type, of 7J-liter capacity, composed of a 
rigid stand supporting the spun-copper autoclave shell, which could 
be securely closed by clamping on a bronze head or cover, the seal 
being secured by polished surfaces between the body and the head. 
The head was provided with a pressure gauge and thermometer well. 
A gas burner underneath the shell served to heat the charge to any 
desired temperature or pressure. 
The method of operation is to place a certain weight of material 
hi the body, to cover with a soda solution containing sufficient 
caustic soda to completely reduce the material, to securely close the 
autoclave, and, by means of the gas burner, to heat the entire charge 
to a definite temperature or pressure. This pressure is maintained 
the required number of hours, after which the charge is allowed to 
cool and the contents are removed and washed free from the dark-, 
colored spent soda solution known as black liquor. Undercooked 
pieces of grass, which are invariably present, are separated from the 
pulp by screening through a No. 10 screen, in which the slots are 
0.01 of an inch wide. 
If the material under examination contains pith cells which by 
reason of their high percentage or quality tend to impart undesirable 
qualities to the finished sheet, it will be necessary to separate them 
from the true fiber at this point. Separation can readily be accom- 
plished by manipulating the pulp on a 60 or 70 mesh wire cloth with 
a stream of water, whereby the small pith cells are washed away, 
leaving the long, true fibers on the wire. In the case of zacaton it 
does not appear necessary or advisable to separate the pith, and it 
was done only in cook No. 1. 
In autoclave cook No. 1, 404 grams of grass, bone-dry basis, were 
treated with 24.4 per cent of caustic soda at a concentration of 19.7 
