Butler and Sheridan — Account of a Neiv Oedanoineter. 469 



poreuse, elle fera nionter I'index et pourra se mesurer par la dimimition de 

 longueur de la colonne d'air. Cela fait, je plonge I'appareil dans un vase 

 plein d'eau. 



" Anssitot cette eau penetre dans les pores, refoule a I'interleur I'air qu'ils 

 contenaient, et la pression augmente progressivement. Au bout de quelques 

 jours elle est devenue egale a 3 ou 4 atmospheres, dans la plupart des cas ; 

 elle en atteint 5 avee Toxyde de zinc ; elle en d^passe 6 avee Famidon." 



Experiments carried out on peas with this apparatus registered a pressure 

 of 234 pounds per square inch. The levers used at first, however, were badly 

 bent by the pressure, and the balance was stretched beyond its capacity, so 

 that the pressure recorded was not even approaching the maximum. In 

 other experiments on the measurement of the swelling force of seeds — for 

 example, those carried out by Macdougal (11) — no packing material appears 

 to have been used. In this case the seeds can swell considerably by becoming 

 polyhedral without necessarily exercising much pressure on the piston. 



If a number of equal spheres are arranged one directly over the other, 

 the pore space is at a maximum and occupies 47"64 per cent, of the total 

 volume ; however, when the splieres are arranged as shot is piled, this space is 

 reduced to a minimum of 25'95 per cent. [Hall (9).] 



lu order to determine experimentally the relative proportion of pore 

 space existing between seeds, we packed a number of peas at random, but 

 as tightly as possible, into a glass-measuring cylinder of three inches 

 diameter until they reached a height of five inches (this gives approximately 

 the size and shape of the reservoir of apparatus described). Keeping them 

 pressed down with a piston, we poured in mercury to the same height, so that 

 all the spaces were filled. The volume of the mercury thus gives tlie total 

 volume of the pore spaces. In the ease of peas, this volume was found to be 

 approximately 34 per cent, of the apparent total volume or one half the actual 

 volume of the seeds. This result is slightly below the mean of the theoretical 

 maximum and minimum quoted above. 



The figures given by Hall apply only when the diameter of the sphere is 

 very small compared with the size of the containing vessel. If, however, an 

 allowance is made for the shape and sides of the vessel, and the peas are 

 regarded as spheres of quarter-inch diameter, the calculated minimum pore 

 volume is considerably increased. Further, the smaller the cylinder, or the 

 larger the seeds, the greater the percentage of the minimum pore volume 

 becomes. Hence if a smaller cylinder were used the results obtained would 

 be lower. For this information we are indebted to Prof. H. C. McWeeuey. 

 Thus, were it not for the sand, seeds could expand fifty per cent, of their 

 volume without necessarily exerting much pressure on the piston. 



SCIENT. PEOC. B.D.S., VOL. XIV., NO. XXXV. 4 E 



