WITH SOLUBLE LEAD SALTS. 359 



of carbonate of lime can be dissolved, independently of the continued presence of 

 the free acid, to cause the appearances referred to. 



I next tried the solvent action of water alone on finely divided carbonate of 

 lime. Distilled water, which had been boiled and cooled, was left in contact 

 with marble in impalpable powder for several days in a close vessel. It was 

 then found by the action both of acetate of lead and of oxalate of ammonia, that 

 rather more carbonate of lime had been taken up by the pure water than was left 

 in solution after boiling the carbonated water, but still that the amount was con- 

 siderably less than the reactions which have been referred to, indicate in ordi- 

 nary natural waters ; and it is remarkable that the effect of the lead salt is usually 

 more decided than that of the oxalate. 



I incline, therefore, to think, that the carbonate of lime present, in such cir- 

 cumstances as have been described, has a different origin, viz.. Double Decompo- 

 sition, between a lime-salt and a carbonated alkali ; as it would seem that the 

 carbonate of lime formed is, in this kind of nascent state, dissolved more readily 

 than when precipitated by boiling from a carbonic solution. The following expe- 

 riments illustrate this origin of the reaction. To half an ounce of distilled water, 

 a few drops of a solution of sulphate of lime in water were added. A single drop 

 of solution of chloride of calcium, and a single drop of solution of carbonate of 

 potash were then added. The liquid remained quite transparent, and did not 

 affect turmeric or cabbage paper. When boiled it still remained transpai-ent. 

 When a drop of solution of acetate of lead was added to a portion of this liquid, 

 either before or after boiling, a considerable Avhite cloud was formed, which dis- 

 appeared on the addition of a drop of acetic acid. Thus was the reaction of the 

 spring waters exactly imitated. I at first inclined to think that in such cases no 

 actual double decomposition ensued until the liquid was concentrated by heat, 

 and that the action on the lead-salt was due to the carbonated alkali present. 

 But farther experiments lead me to believe that the carbonate of lime is actually 

 formed, at least to a considerable extent, and then dissolved by the water ; for, 

 if a couple of drops of solution of chloride of calcium and a drop of solution of 

 carbonate of potash be added to a few drops of distilled water, muddiness will be 

 produced ; and this will disappear when half an ounce of distilled water is 

 shaken with the mixture, without any deposit being formed by rest. The solution, 

 however, of the carbonate of lime is dependent on the action of the water taking 

 place either on the nascent salt, or at least immediately after its formation ; for I 

 found that when carbonate of lime, precipitated by double decomposition, was col- 

 lected on a filter, washed, and allowed to stand some minutes, and then left in con- 

 tact aU night with boiled and cooled distilled water, acetate of lead had only a 

 very feeble effect on the liquid. 



It was, of course, necessary, in order to establish this view, to ascertain that 

 those natural waters which exhibit the reaction referred to, actually contain 



