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VII. 



NOTE ON THE TENSILE STEENGTH OP WATER. 



By HENRY H. DIXON, Sc.D., F.R.S., 

 Professor of Botauy in tbe University of Dublin. 



Read January 26. Ordered for Publication Feekuauy 9. Published April 5, 1909. 



Donny/ in 1846, found that it was possible for a column of sulphuric acid 

 1'255 m. long to hang in a vertical glass tube sealed at the upper end, even 

 when the atmospheric pressure was removed from the lower open end. He 

 explained this phenomenon as due to the adhesion of the sulphuric acid to the 

 glass and to the cohesion of the liquid itself. 



He compares this behaviour of the sulphuric acid to the well-known 

 experience that the mercury in a barometer is retained above the actual 

 barometric height, if the tube, completely filled by inclining it, is gradually 

 raised to a vertical position. He further points out that this phenomenon 

 has been explained by Laplace, as due in a similar manner to the adhesion 

 of the mercury to the glass and to its own coliesion. 



Donny points out that when one withdraws a plane disc from contact 

 with a surface of water, the cohesion of the latter does not come into play ; 

 but the column of water connecting the disc with the liquid below at first 

 grows gradually thinner until, at a moment when the disc has been raised to a 

 certain heiglit above the general level of the lower liquid, the column spon- 

 taneously draws in from the edges of the disc, and when its diameter becomes 

 extremely small, breaks in two. He also shows that, in a tensile liquid 

 column a bubble, sufficiently small to have surface-tension forces capable of 

 supporting the hydrostatic head of the liquid below, will not destroy the 

 tensile state. He, however, failed to demonstrate the cohesion of water by 

 the same method which had been successful in the case of sulphuric acid. 



But he points out that the coliesion of water may be observed in another 

 way. A straight glass tube sealed at both ends, partly filled with water, 

 and enclosing some air, is supported vertically in one hand of the experi- 

 menter, while he vigorously strikes the lower end with the palm of the other 



F. Donny, Sur la cohesion des liquides, et sur leur adherence aux corps solides. Ann. de 

 Chimis et de Physique, ser. 3, tome xvi., 1846, pp. 167 et seq. 



