332 



Scientific Proceedings, Royal Dublin Society. 



weighed again, W« ; exposed to air at normal condition for t 2 hours ; then 

 finally weighed, W z . The total surface A sq. cms. of the sample was also 

 calculated. 



The following results were obtained for three samples of erinoid in the 

 form of short cylindrical rods of diameter about 2-5 cms. 



A = 66 sq. cms., t t = 73 hours, t 2 = 25'5 hours. 



in which x = W 2 - W x the water absorbed in 73 hours, and y = W% - W 3 

 the water lost in the succeeding 25 - 5 hours on exposure to normal air. 



The percentage gain in weight due to the absorption of water in 73 hours 

 100a: 



was therefore 



W x 



and the percentage loss of the water absorbed due to air 



drying for 25 - 5 hours was 



100?/ 



Thus, for the three samples the following values are calculated : 



Of these, the red variety is the most absorbent and the most retentive of 

 water. The blue, a dark blue, and the black are much more nearly equal in 

 these respects. 



To confirm the result that red was more absorbent of water than blue 

 erinoid, a second experiment was made with samples of erinoid in sheet form, 

 each of total surface-area of about 135 sq. cms. The results obtained were : — 



