284 Air. T. Tate's Experimental Researches on 



thoroughly dried, I have found that calico, linen, unsized paper, 

 and other substances of this kind absorb and retain about their 

 own weight of water ; woollen cloth about twice its own weight ; 

 bath brick and fine sand about one-third their own weight; 

 plaster of Paris, after being set, about six-tenths ; common deal, 

 six-tenths ; laurel-wood rather more than two-thirds ; pine-wood 

 nearly six-sevenths; and bran, about three and three-quarters. 



In order to determine the porosity of different substances, so 

 far as regards their capacities for absorbing water, we have the 

 following formulae : — 



V ^^F~^ xY > andv = (s 2 - 5l )V; 



where V= the volume of the body; v= the capacity of the 

 interstices of the body, or the volume of that portion of it pene- 

 trated by the water absorbed ; w = the weight of the body in a 

 dry state, s x being its corresponding specific gravity; w^— its 

 weight when perfectly saturated with water, s 2 being its corre- 

 sponding specific gravity ; and w x = the weight of the body in 

 water. 



By means of these formulas and the experimental data, I have 

 found the following results : — 



For woollen cloth, v = |V; that is, the interstices are three- 

 fourths of the whole volume of the substance. 



For bath brick, v=' 2 V; that is, the interstices are two-fifths 

 of the whole volume of the substance. 



For fine sand, v = '4<7 ; that is, the interstices are nearly one- 

 half of the whole volume of the substance. 



For deal, v=^V; for laurel- wood, v = *45V; and for pine- 

 wood, v = -|V. In these cases, however, a slight allowance must 

 be made for the expansion of the wood by the absorption. 



Contraction and elongation of textile fabrics by the absorption of 



moisture. 



Under a constant stretching force, calico, linen, flax, and 

 unsized paper undergo contraction upon the absorption of 

 moisture, whilst certain woollen fabrics undergo elongation. 

 Thus strips of linen and calico were contracted about the -pj- th 

 part of their length, whilst strips of woollen cloth were elongated 

 nearly the same proportional part of their lengths by the absorp- 

 tion of moisture. Threads of cotton and flax were contracted 

 about -g-^th^part of their lengths. 



The strips as well as the threads were suspended from one 

 extremity, and had metal plates attached to their lower extremi- 

 ties, so as to give the material a uniform tension. The divisions 

 of the scale, measuring the lengths of the strips, were divided 



