﻿The Solubility of Calcium Carbonate in Water. 959 



degree of the temporary hardness) is a matter of great im- 

 portance. If the sample is boiled for some time the dissolved 

 carbon dioxide is expelled, and the greater part of the 

 temporary hardness is destroyed by precipitation of the 

 calcium carbonate, but some will still remain in solution. 

 The amount of this must be known before the values of the 

 temporary and permanent hardness of the water can be 

 calculated ; it has been roughly estimated at *02 gr. per litre. 

 Measurements of the solubility of calcium carbonate at other 

 temperatures and under ordinary conditions are altogether 

 lacking. 



At the suggestion of Professor Walker, I have attempted 

 the direct estimation of the solubility of calcium carbonate 

 in water. Experiments have been made, at temperatures 

 between 25° 0. and the boiling-point, upon all three varieties 

 of the substance — calcite, arragonite, and the amorphous 

 form ; also upon solutions of the bicarbonate, in equilibrium 

 with air free from carbon dioxide and with atmospheric air. 



The method of procedure was, briefly, as follows: — a 

 large volume — 2 to 3 litres — of the saturated solution was 

 prepared in a large silica flask, and filtered off into a second 

 silica flask containing a small excess of acid; the liquid was 

 evaporated to small bulk — 50 to 100 c.c. — and titrated 

 against a known solution of baryta. 



It is the use of silica vessels that renders this direct deter- 

 mination possible; with glass or porcelain vessels the solution 

 would dissolve out alkali, during concentration, sufficient to 

 vitiate the results entirely. The silica flasks u^ed were of 

 three to four litres capacity; their resistance to neutral, acid, 

 and alkaline solutions of the concentrations existing in the 

 subsequent experiments was first tested as below. 



Neutral Solution. — Water of specific conductivity 

 1*25 x 10 ~ 6 can be obtained by one distillation from tap- 

 water by the addition of 10 c.c. Nessler's solution to two 

 litres of water. Jena glass vessels and a tube of pure tin, 

 fitted with a condenser, are employed ; the distillation is 

 carried out in the open air, and the first third ot the distillate 

 rejected. On redistillation of this water from one silica 

 vessel to another, by means of a silica hood carefully ground 

 on the neck of the first vessel, water of a specific con- 

 ductivity '85 X 10 " 6 was obtained. If half of this distillate be 

 boiled away, the residue possesses a specific conductivity of 

 •70xl0 -6 , which is the conductivity value for the purest 

 water that can be obtained in contact with air. This shows 

 conclusively that pure water dissolves no conducting material 

 from a silica vessel. 



