On the Precipitate produced in Water by Acetate of Lead. 125 



of lime. To know whether it arises from the water redis- 

 solving carbonate of lime, which had been held dissolved by 

 carbonic acid and then precipitated by boiling, I transmitted 

 a current of carbonic acid through lime water tilLit completely 

 redissolved the precipitate which had at first formed. I then 

 boiled the solution for a short time, as in experimenting 

 with the spring waters, and filtered the liquid; but although 

 it was slightly precipitated by acetate of lead, the effect was 

 very much less than that on common water ; showing that we 

 cannot account for the effect on common water by supposing 

 that all the carbonic acid had not been driven off by the ebul- 

 lition. Again, when distilled water was left in contact with 

 marble in impalpable powder for several days, both acetate of 

 lead and oxalate of ammonia showed less lime than in the 

 common waters, although rather more than in the lime-water 

 experiment. I incline therefore to think that the carbonate 

 of lime owes its origin to double decomposition between an 

 alkaline carbonate and a lime salt, such as a chloride. If to 

 a few ounces of distilled water a drop or two of muriate of 

 lime and a drop or two of carbonate of soda be added, the 

 liquid remains quite transparent ; and the reaction of common 

 water with acetate of lead and acetic acid may be exactly imi- 

 tated with this liquid. And in all the common waters yielding 

 the reaction, I could detect alkalies in union with acids. 



The common water of the town of St. Andrews, I found, 

 after being boiled and filtered, to yield by evaporation -^j^-^-^ 

 of carbonate of lime; and other well and river waters may 

 contain still more. Fresenius has stated that water is capable 

 of holding in solution yy^oT ^^ carbonate of lime, after being 

 saturated with that salt by long-continued boiling, and left 

 in contact for four weeks with the deposit formed on cooling. 

 Nature of course does not take such pains to charge spring 

 waters with lime ; and I think the method I have suggested 

 affords a much more simple and probable means of effecting 

 this end. 



The St. Andrews' water also contains a trace of carbonate 

 of magnesia after being boiled and filtered ; and it is probable 

 that this substance may sometimes be in part the cause of the 

 reaction referred to, but to a much less extent*. 



* I have given fuller details on this subject in a paper inserted in the 

 Transactions of the Royal Society of Edinburgh for the present year. 



