HEMP HUEDS AS PAPER-MAKIISTG MATERIAL. 13 



It is well known that the method of conducting tests necessarily 

 varies with the size of the test. In the matter of yield determination, 

 for example, laboratory tests may be on such a small scale that the 

 weighing and sampling of the resulting cellulose fibers may be con- 

 ducted by means of chemical laboratory apparatus and analytical 

 balance, while in tests involving a matter of 5 to 10 pounds of material 

 larger and different types of equipment are necessary. When 

 the tests are so increased in size as to employ 300 or 400 pounds, 

 still other t3rpes of equipment are necessary for the treatment of 

 the material and for a determination of the yield of fiber. In 

 tests involving tons of material the equipment involves the use of 

 machines. Accuracy in degree of control and in results will vary 

 materially with the size of the test. As the size of the test increases, 

 certain factors will vary in a beneficial manner, while others will vary 

 in a detrimental manner, so it is a question for each investigator to 

 decide, after taking all factors into consideration, as to the size of 

 test which will give the most satisfactory results. In work of this 

 nature it is found, on the whole, that better results are obtained in 

 large tests, although the control of the factors and the determination 

 of the yield of fiber are more difficult than in smaller tests. 



In the tests described in this bulletin, the Department of Agricul- 

 ture employed a rotary digester of its own design,^ comprising a shell 

 5 feet 5 inches in length by 4 feet in diameter, capable of holding 

 about 300 pounds of air-dry hurds. It is believed that a test of this 

 size is large enough to give satisfactory results and that the results 

 are susceptible of commercial interpretation, while at the same time 

 they are sufficiently small for complete control and to afford fiber- 

 yield figures which are both accurate and reliable. Two such rotary 

 charges gave enough 'fiber for one complete paper-making test. 



OPERATIONS INVOLVED IN A TEST. 



A complete test on hurds comprises seven distinct operations, and 

 the method will be described, operation by operation, in the order 

 in which they were conducted. 



Sieving. — The hurds for the first test were not sieved to remove 

 sand and dirt, but the resulting paper was so dirty that sieving was 

 practiced in aU subsequent tests. The hurds were raked along a 

 horizontal galvanized-iron screen, 15 feet long and 3 feet wide, with 

 11 i meshes per linear inch, the screen being agitated by hand from 

 below. Various amounts of dirt and chaff could be removed, depend- 

 ing on the d(;grce of action, but it was found that if much more than 

 3 per cent of the material was removed it consisted chiefly of fine 

 pieces of wood with practically no additional sand or dirt; in most of 

 the tests, therefore, the material was screened so as to remove 



' For a description of this rotary digester, see Brand, C. J., and Merrill, J. L., Zacaton as a paper- 

 making material, U. 8. Dept. Af;r. Bui. 3CX», p. 2S, 1915. 



