26 



BULLETIN 309, U. S. DEPAETMENT OF AGEICULTUKE. 



which can be maintained accurately at a constant temperature and 

 relative humidity, conditions which are absolutely essential to com- 

 parative and absolute paper testing. 



The sample designated as No. 41 was manufactured from the com- 

 bined 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. 

 11, 12, 13, and 14. The report of the Leather and Paper Laboratory 

 on these samples is shown in Table VIII. 



Table VIII. — Physical properties of six paper samples made from zacaton pulp, accord- 

 ing to tests conducted hy the Leather and Paper Laboratory of the Bureau of Chemistry. 











Bursting strength. 



Strength 





Folding endur- 

 ance 



Folding factor. 



L. and 



Mark 

 No. 



Ash. 



Weight, 



25x38, 



500. 





factor, 

 per wt., 

 25x38. 



Thick- 

 ness. 







P. No. 



Aver- 



Maxi- 



Mini- 



Trans- 



Longi- 



Trans- 



Longi- 











age. 



mum. 



mum. 







verse. 



tudinal. 



verse. 



tudinal. 







Per ct. 



Lbs. 



Pts. 



Pts. 



Pts. 















30612 



41 



19.5 



51.0 



28.0 



29.0 



27.0 



0.55 



36 



27 



42 



0.53 



0.82 



30613 



41 



19.4 



49.5 



25.5 



27.0 



24.0 



.52 



34 



25 



39 



.51 



.79 



30614 



41 



19.2 



51.0 



27.5 



29.0 



26.0 



.54 



37 



38 



35 



.74 



.69 



30615 



76 



22.4 



52.5 



13.0 



14.0 



12.0 



.25 



40 



4 



3 



.08 



.06 



30616 



76 



22.5 



57.0 



14.0 



14.0 



14.0 



.25 



38 



4 



3 



.07 



.05 



30617 



76 



21.4 



52.5 



13.5 



14.0 



13.0 



.26 



39 



3 



3 



.06 



.06 



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 

 filler 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 

 machine-finish printing paper, although the ash is four times that of 

 this grade. The folding factor is likewise higher than is specified for 

 a first-grade machine-finished printing paper. 



Sample No. 76, according to the same classification, would f aU 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 

 specifications, therefore, are somewhat different and more rigorous 

 than would have been the case had it been the intention to apply 

 them to the general run of commercial papers. 



According to present commercial usage, sample No. 41 would be 

 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 



