374 Prof. F. Clowes. Deposition of Barium Sulphate 



Though the experiments cannot be quoted as confirming the chemical 

 hypothesis, which I still think to be supported by an overwhelming 

 weight of evidence, it has been thought worth while to describe them, 

 if only to show the extreme difficulty of eliminating the last traces of 

 active matter from the gas employed. That this is the real difficulty 

 in the way of obtaining positive results is well illustrated by the 

 ingenious experiments of C. Christiansen.* He found, among other 

 things, that when the metal (of a pair) near which positive potential is 

 usually observed is exposed, for a minute fraction of a second, to an 

 inactive gas, such as hydrogen, the observed potential difference is 

 very much smaller than when the exposure lasts for a considerable 

 time. The metal exposed by Christiansen was a jet of liquid amalgam, 

 flowing from a drawn out glass tube. Its surface was thus perfectly 

 clean, and the time of exposure to the surrounding gas was merely the 

 interval between the instant at which the amalgam left the nozzle and 

 that at which it broke into drops. The difference of potential observed, 

 when carbon was opposed to a jet of zinc amalgam in hydrogen in this 

 manner, was only 0'15 volt; while in air it was '89 volt. If more 

 time had been allowed, the impurities in the hydrogen would have 

 diffused in larger quantity towards the zinc, and given a larger effect, 

 similar in character to that observed in my experiments, where the 

 metals are exposed to the gas for a period amply sufficient for all such 

 action. 



"Deposition of Barium Sulphate as a Cementing Material of 

 Sandstone." By FRANK CLOWES, D.Sc., Emeritus Professor, 

 University College, Nottingham. Communicated by Professor 

 H. E. ARMSTRONG, F.E.S. Eeceived February 7, Eead 

 February 23, 1899. 



Some years ago I described the occurrence of a peculiar sandstone 

 over a large area in Bramcote and Stapleford, near Nottingham.! The 

 sandstone was remarkable for its high specific gravity, and chemical 

 analysis, supported by microscopical examination, proved that the 

 high specific gravity was due to the existence in the sandstone of a 

 large proportion of highly crystalline barium sulphate. In the rock 

 itself the percentage of the sulphate varied from 33*3 to 50*1 : and 

 it evidently served as the binding or cementing material which held 

 the sand grains together. The occurrence of this sandstone was stated 

 by geologists to be unique in the United Kingdom. 



Mr. J. J. H. Teall made an examination of a portion of the sand- 

 stone, and stated that after breaking up a portion of the rock, he easily 



* <Wied. Ann.,' vol. 56 (1895), p. 644. 

 f ' Eoy. Soc. Proc.,' vol. 46, p. 363. 



