578 Transactions. 



Conclusions. 



(1.) The solubility of tricalcic phosphate in carbonic-acid solution in- 

 creases directly with increasing pressure of carbon dioxid"e. 



(2.) The solubility also increases with increasing time of contact between 

 solvent and solute. 



(3.) Differences of temperature appear to have very little effect. 



(4.) The solubility is irregular when che surface of the solution-vessel 

 is not uniform throughout a series of runs. 



(5.) The presence of small quantities of copper in solution causes a 

 small decrease in the solubility. 



(6.) An interaction takes place between the tricalcic phosphate and the 

 carbonic acid. 



Notes. 



In (2) practically no difference is observable between a solution run off 

 after standing in the solution-vessel for eighr.oen hours and the same 

 solution after standing forty hours. This is due to the sinking of the 

 undissolved portion of the phosphate to the bottom of the vessel, and the 

 consequent removal from the sphere of action. 



In (3) any increase in solubility with rising temperature is probably 

 counteracted by the concomitant lessened solubility of the carbon dioxide. 



It is suggested that further work might be carried out to determine 

 the solubility with varying times of contact between solid and solvent, and 

 also to ascertain the effect of metallic salts, such as those of ammonium, 

 calcium, and copper. More accurate work also could be done if the vessel 

 were lined with a quite continuous coat of platinum. 



Art. LIIL— On [the Deflection of the Plumb-line from the Vertical due to 

 the Spheroidal Form of the Figure of the Earth, and its Effect on the 

 Latitude of Station? above the Mean Sea-level. 



By W. T. Neill, New Zealand Survey Department. 



[Read before the Otago Institute. 22nd September, 19 J 4.] 



It is now well known that the attraction of mountains and elevated regions 

 has a sensible influence on the plumb-line. These local deflections have 

 been the subject of numerous investigations since 1854, when Archdeacon 

 Pratt computed the effect of the attraction of the Himalaya Mountains 

 on the plumb-line in North India (Phil. Trans., 1854). 



In modern geodetic surveys the degree of precision in the determination 

 of the apparent astronomical latitude by means of the zenith telescope 

 is so great that the station error, as it is called, or the difference between 

 the observed and computed latitudes, due to local causes, has become a part 

 of the routine work. 



The deflection of the plumb-line by the attraction of mountains or by 

 the variation of the density of the underlying strata will not be further 

 discussed, the object of the present investigation being to determine the 



