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 preliminary 

 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 7i-Hter 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 

 in 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 



