Butler and Sheridan — Account of a New Oedanometer. 479 



The error is therefore 1 in 60 for 5° C, 

 or 1 io 300 for 1° C. 



2. Expansion of mercury in iron due to rise in temperature. 

 Volume of mercury in apparatus, . . = 4 c.cms. 



Coefficient of expansion of mercury in iron, . = '000143. 

 Eise in temperature of 5° C. 

 Increase in volume, = 4 x 5 x -000143 cms. = '00286 cms. = 2"8 c.mms. 



Now, one division on our manometer represents 1 c-mm. approximately, 

 hence the expansion of mercury would appear to cause a very serious error — 

 one of from 10 to 20 atmosplieres. In practice this is, however, not the case. 

 The expansion of the mercury causes a rise in pressure in the manometer; 

 but if the seed is unable to support this increased pressure, it loses water 

 and diminishes in volume, thus automatically correcting for the expansion 

 of the mercury, since the volume change is small. 



In support of this view we may point out the uniformity of the readings 

 given in the cases of beans and peas. Beans varied in our latest experiments 

 from 27 to 30 atmospheres pressure when swelling ; while peas varied from 

 48 to 50 atmospheres. These values would vary much more if the mercury 

 expansion effect was appreciable. 



Then the following experiments were carried out : — Two instruments were 

 placed in a water bath, and their temperatures rapidly raised through 10° C. 

 One of the instruments contained some peas which were registering about their 

 maximum pressure — in this case the mercury volume rose only '1 of a division 

 higher. In the second instrument the reading was low at the start — in this 

 case the mercury went up 4 graduations. If the seeds did not reduce in 

 volume, the mercury would have gone up in the first instrument as much as 

 it went up in the second one. 



We now carry out the experiments in an incubator, and keep it at a 

 temperature of 20° C. constant to a degree, to avoid this source of error. 



LiTEKATURE CiTED. 



(1) Atkins, W. E. Gelston. — The Absorption of Water by Seeds. ScLProcEoy. 



Dublin Soc, N.S. xii: 35-46. 1909. 



(2) CoupiN, H. — Sur les variations du pouvoir absorbant des graines en rapport 



avecle ur poids. Bull. Soc. Bot. de Prance xl : 102-104. 1893. 

 (3) Sur I'eau libre dans les graines gonflees. Bull. Soc. Bot. de France 



xli: 91-93. 1894. 

 (4) Eecherches sur I'absorption et le rejet de I'eau par les graines. Ann. des 



Sci. Nat., Bot., Serie 8. Tome ii : 129-222. 1895. 



