40 BULLETIN 882, U. S. DEPARTMENT OE AGRICULTURE. 
For the comparative tests, fabrics made from Sakellaridis Egyp- 
tion, Sea Island, and American Egyptian cottons according to the 
Signal Corps specifications (a) and (5) were doped in the manner 
described above. These tests indicated that the lowest stretch was 
obtained with cloth made from the Sakellaridis Egyptian cotton, and 
the greatest with cloth composed of the American Egyptian, although 
there was very little difference between the sea island and the Ameri- 
can Egyptian. 
For the tests to determine the best weave, cloths made of similar 
.S/SO's mercerized yarn were used and the following were studied : 
Plain weave made according to Specifications 16,005-A: 2/2 basket 
weave of 68 ends by 68 picks per inch ; and 2/2 twill of 68 ends by 
68 picks per inch. Accepting as the proper basis of judgment that 
the highest tensile strength combined with the least stretch is best for 
airplane fabrics, and without considering the tendency of the fabric 
to draw when stretched on the panel of the airplane frame, these 
tests indicated that the basket weave was the best for the purpose. 
In general, they confirmed the results previously obtained upon the 
fabrics before doping, and thus show that the stretch-stress relations 
of the fabric are changed only in quantity by doping. 
Having determined the best commercial variety of cotton and best 
weave for airplane fabrics, efforts were then turned toward deter- 
mining the relation of the various contributing agents to the final 
result. The following points were studied : 
(a) Influence of the percentage of dope applied. 
(&) Influence of the doping material. 
(c) Influence of the stress conditions before doping. 
From these investigations it was determined that increasing the 
percentage of dope beyond 117 per cent did not improve the stretch- 
stress qualities of the doped fabric, but increasing the per cent of 
dope to this amount had decreased the stretch considerably, although 
the weight of the fabric had been thereby greatly increased (com- 
pare Figs. 20 and 21) ; that the nitrate dope produced slightly bet- 
ter results than the acetate dope, together with improved properties 
from varnishing (Fig. 21) ; and that stretching the fabric before 
doping reduced materiallv the stretch component of the doped fabric 
(Fig. 22). 
