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BULLETIN

309,

U.

S.

DEPARTMENT OF AGRICULTURE.

which can be maintained accurately at a constant temperature and which are absolutely essential to comparative and absolute paper testing. The sample designated as No. 41 was manufactured from the combined pulps of cooks Nos. 7, 8, 9, and 10, and the sample designated as No. 76 was manufactured from the combined pulps of cooks Nos. The report of the Leather and Paper Laboratory 11, 12, 13, and 14. shown in Table VIII. is samples these on

relative humidity, conditions

Table VIII. ing

to tests

Physical properties of six paper samples made from zacaton pulp, accordconducted by the Leather and Paper Laboratory of the Bureau of Chemistry.

Bursting strength. L. and P. No.

Mark Ash. Xo.

500.

factor,

Aver- Maxiage.

Per -30612 30613 30614 30615 30616 30617

ct.

41 41 41

19.5 19.4 19.2

76 76

22. 4

76

22.5 21.4

Lis. 51.0 49.5 51.0 52.5 57.0 52.5

Folding endur-

Strength

Weight, 25x38, Mini-

per wt., 25x38.

ance.

Pts.

Pts.

28.0 25.5 27.5 13.0 14.0 13.5

29.0 27.0 29.0 14.0 14.0 14.0

27.0 24.0 26.0 12.0 14.0 13.0

55 .52 .54 .25 .25 .26

0.

factor.

ness.

Trans-

Longi-

Trans-

Longi-

verse.

tudinal.

verse.

tudinal.

mum. mum.

Pts.

Folding

Thick-

36 34 37 40 3S 39

27 25 38

42 39

0.53

0.82

35

.51 .74

4 4

3 3 3

.08 .07 .06

.79 .69 .06 .05 .06

3

Sample No. 41 contains the ash specified for a coated paper, namely, 20 per cent, although some uncoated book papers carry nearly this quantity. Practice varies in the different mills, some using more than others for the same general grade of paper. This sample shows a strength factor, which is the bursting strain divided by the ream weight, which is higher than that specified for a first-grade

filler

machine-finish printing paper, although the ash this grade.

The

folding factor

is

is

four times that of

likewise higher than

is

specified for

a first-grade machine-finished printing paper.

Sample Xo.

76, according to the

same

classification,

would fall below

the fourth-grade machine-finish printing paper. It should be noted here, however, that at the time the specifications of Report No. 89 were drawn up, the chief object was to secure better papers in general for the use of the United States Government. The

somewhat different and more rigorous the case had it been the intention to apply have been than would them to the general run of commercial papers. According to present commercial usage, sample No. 41 would be

specifications, therefore, are

regarded as much better than a first-grade machine-finish printing paper and No. 76 would be classed as a second-grade machine-finish printing paper