TRANSACtlOJJS OF SECTION B. 705 



2; On Recent Developments in the Textile Industries. 

 By Dr. A. Liebmann. 



3. Injluence of Pressure on the Formation of Oceanic Salt Deposits, 

 By H. M. Dawson, Ph.D., B.Sc. 



The present paper forms one of a series of investijrations carried out with a 

 view of obtaining information in regard to the conditions of formation of the 

 ytassfiirt deposits. 



In previous papers (van't Hoff and pupils) the isothermal equilibrium relation- 

 ships of salts occurring in sea-water and the intluence of temperature on these 

 has been investigated. This paper deals with the influence of pressure. 



One of the last phases of salt deposition in the Stassfurt layer is represented 

 by tachhydrite (CaCl., SMgCl, li'H.,0) ; experiment shows that this separates 

 from solutions of the mixed chloride of Ca and Wg if the temperature exceeds 

 22°-4 C. 



Below 22°'4 C. a mixture of the simple salts separates, but no tachhydrite. If 

 the mixed chlorides be heated in the solid condition, then at 22° 4 C. water is 

 split off and tachhydrite is formed. 



The influence of pressure on the temperature of formation of this double salt 

 has been studied. 



Careful determinations by the thermometric method show that under atmo- 

 spheric pressure this tearperature is 22°'400 C. 



By means of the manokryometer the temperature of formation under higher 

 pressures was determined. 



The mean result of this direct determination of the influence of pressure is 

 that for an increase of 100 atmospheres the temperature of formation is raised 

 1°-02C. 



Another and indirect determination is possible by applying the formula of 

 Thomson for the influence of pressure on the melting point to the trausiiion 

 temperarure at which calcium chloride, magnesium chloride, tachhydrite, and 

 saturated solution are in equilibrium. From the formula in question, viz., 



dT _ 1033-3 (f,-r,) 

 dp 426U0 q ' 



the determination of - - only involves the knowledge of the change of volume and 



'^P . . . 



the heat change accompanying the reaction, which takes place according to 



CMgCI.GII.p + l-188CaClo6ILO 



Saturated Solution. 

 ■252CaCl,2]\IgCl,-12H,-,0 + -101(10011,0 9-27 CaClj4-92 MgCL) + y Cals. 



The estimation of [v.. - «,) and of a from a aeries of experiments and substitu- 



dT 

 tion m the thermodynamic formula gives for — the value -OISS" C. In other 



dp 



words, ]00 atmospheres would raise the temperature of formation l°-o.5 C. 



Both results show tljat the influence of pressure on the separation of salts 

 from solution is very small in comparison with the influence of temperature. 



On thermodynamic grounds it can be shown that the influence of jjressure on 

 temperature displacement in the case of other salts must be of the same order of 

 magnitude as that found in the case of tachhydrite. 



The fact that certain Stassturt salts {e.g., Kieserte, Kainite, Loweite and 

 Langbeinite) are not deposited on evaporation of sea-water at a constant 



1900. z z 



