Skey. — On the Soli(biliti/ 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 

 35,000 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 succinctly 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 

 fi-'eshly 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 

 time. 



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. LXYII. 



