﻿960 Mr. J. Kendall on the Solubility of 



Acid Solution. — 10 c.c. of decinormal sulphuric acid were 

 added to about two litres of water in one o£ the vessels, and 

 the solution evaporated down to 50 c.c. On titration against 

 baryta, with phenolphthalein as indicator, the existence of 

 the original amount of acid in the solution (within limits of 

 experimental error) was established. 



Alkaline Solution. — Two litres of calcium hydroxide solu- 

 tion of concentration *001 N were boiled in the silica vessel 

 for some time, and then, after a known excess of sulphuric 

 acid had been added, evaporated to small bulk. On titration 

 against baryta, with phenolphthalein as indicator, the required 

 excess of acid was found to exist in the solution. 



The silica flasks are therefore not attacked, to any appre- 

 ciable extent, by solutions of the above concentrations, and 

 these were never exceeded in subsequent experiments. 



The sulphuric acid used throughout was of approximately 

 decinormal concentration, the baryta solution of approxi- 

 mately centinormal. Phenolphthalein was employed as 

 indicator. All water used was freshly distilled, and collected 

 directly into one of the silica flasks. 



Mineral Calcite and Arragonite. 



The calcite used consisted of large, transparent crystals 

 of iceland-spar (density 2*72) ; the arragonite was a fine 

 museum specimen (density 2*90), which showed no traces 

 of strontium when tested by the spectroscope. Both minerals 

 were finely powdered in an agate mortar. Successive ex- 

 periments with the same sample of solid led to constant 

 solubility results — a most rigorous test of purity. Experi- 

 ments were carried out at three temperatures : 25° 0., 50° C, 

 and 100° 0. 



For the determination? at 100° 0. a small quantity of the 

 powdered substance was added to water at the boiling-point, 

 and after the boiling had been continued for periods varying 

 from 40 to 200 minutes, the solution was filtered off from 

 the remaining solid. For those at 50° 0. and 25° C. the 

 silica vessel was immersed in a thermostat at the particular 

 temperature, and fitted with a rubber cork, through which 

 passed two silica tubes, one short and the other reaching to 

 the bottom of the flask. The solution could thus be kept 

 agitated by a current of pure air drawn through the apparatus; 

 the air being led, from outside the building, through a long 

 tube packed with cotton-wool, a wash-bottle containing 

 Nessler's solution, two soda-lime towers, and finally a wash- 

 bottle containing pure water, before entering the solution. 

 Equilibrium was established much more slowly at these 



