Sxey.—On the Solubility of Earthy Carbonates in Pure Water. 453 
consider this question to be settled, at any rate not authoritatively so; thus 
the degree of solubility of calcic carbonate in pure water, as assigned by 
Fresenius, is one part in 10,601 parts of water, and by Bloxham, one part in 
85,000 parts, while one in about 23,000 parts is generally taken as the 
datum wherewith to compute the quantity of this compound present in sea- 
water, or about three grains per gallon. 
Now these statements are, as you perceive, of a very conflicting 
character, and upon coupling the knowledge of this fact with that of the 
very decided solvent effects of many alkaline salts upon calcic carbonate (as 
shown in my last paper to this Society," I became impressed with an 
idea that in the case of the earthy carbonates generally those results 
upon which the higher ratios of solubility were based had been vitiated by 
the action of one or more of such salts in the test liquid used, a certain 
quantity of the carbonate tested being dissolved thereby, which, added 
to that capable of being dissolved by pure water, raised the quantity 
dissolved to one proportionately greater than that proper to assign to such 
carbonates. 
Under this impression I investigated the matter for myself, and whether 
my hypothesis be right or not, it was soon ascertained beyond doubt that 
these higher ratios are wholly erroneous, and not only this, but that even 
in most cases the lower ones are greatly over-stated. 
The actual results of this investigation, together with the method used 
therein, I will now proceed to state as succinetly as possible. 
First, then, as to the method :— 
I make up a solution of the earth, the carbonate of which is to be tested, 
to a certain strength, as a chloride, also a very weak solution of car- 
bonate of soda or of lithia. Both solutions are boiled for a long time to 
expel any free carbonic acid present, and afterwards allowed to cool to a 
common temperature. The solution of earthy chloride I then dilute with 
freshly distilled water applied successively in small and measured quantities, 
until the last portion sampled therefrom when mixed with the carbonate 
manifests but the faintest cloudy appearance (indicating a precipitate of 
carbonate) when viewed in a large bulk and after the lapse of a considerable 
tim: 
e. 
Now it is obvious that so long as the slightest cloud is formed under 
these circumstances, the whole of the earthy carbonate which is produced 
by the interaction of the salts used is not dissolved, a minute quantity being 
thrown out of solution, and so by computing the quantity of earthy 
carbonate present in a certain volume of the liquid we have an approximate 
estimate of the solubility in water of the earthy carbonate with which we 
* Vide Art. LXVII. 
