On a Semi-automatic High-Pressure Installation. 153 



rise in resistance which may continue for a considerable 

 time. Evidence is given that this phenomenon is intimately 

 connected with the sorption of gas by the film. 



The above experiments were carried out in the Physical 

 Laboratory of the University of Bristol, under the direction 

 of Dr. A.M. Tyndall. I am greatly indebted to him for the 

 help and encouragement that he has given me throughout the- 

 work. My thanks are also due to Mr. J. D. Fry for his help 

 in the earlier stages of the work, particularly in the con- 

 struction of the apparatus. 



The expenses of the research were defrayed by a grant 

 from the University of Bristol Colston Society. 



April 20th, 1916. 



XII. A Semi-automatic High-Pressure Installation. 

 By The Earl of Berkeley, F.R.S., and C. V. Burton, H.Sc. 



A 



S the primary object of the installation was to deter- 

 mine the compressibilities of solutions, we add to the 

 description of the pressure-apparatus itself details of two 

 devices found useful in this connexion. 



Previous workf on the subject has shown us that when 

 altering the pressure, the alteration must take place slowly;., 

 otherwise, the mercury rising in the capillary of the piezo- 

 meter will leave behind it an appreciable quantity of the 

 solution clinging to the walls, and thus vitiate the estimation, 

 of the change of volume. The method by which this is 

 overcome is given in some detail on p. 159. Again, when 

 the pressure has been changed, it is essential that the thermo- 

 dynamic heating or cooling brought about thereby should 

 have time to dissipate before the level of the mercury 

 meniscus is read. In other words, the new pressure must 

 be maintained constant for a period of one to two hours ; an 

 automatic device for doing this is shown in fig. 6. 



The general arrangement. — The working fluid is castor oil*, 

 and the pressure is applied by means of a pump made by 

 Messrs. Schaffer and Budenberg. As this pump is of a 

 pattern regularly made and catalogued by the makers, its 



* Communicated by the Authors. 



t This research is not yet published. 



% Ordinary " cold pressed " castor oil becomes somewhat gelatinous 

 under high pressures. If, however, it is cooled to 0° C. until no further 

 precipitate comes out and then filtered, the oil will remain unchanged 

 for quite a long time. 



