CATARACTS, AND INUNDATIONS. 201 



should be saturated with fixed alkalis and with acids, that the preci- 

 pitates be collected, and their nature examined. Bergman appre- 

 hended that the quantity of the principles contained in waters might 

 be judged of from the weight of the precipitates obtained in these 

 mixtures. Several other chemists have likewise employed this me- 

 thod, but always with a view to certain particular circumstances; 

 and no one has hitherto proposed to make a connected analysis of 

 mineral waters by this means. To succeed in this analysis, it would 

 be proper to mix several pounds of the mineral water with each 

 re-agent, till the latter ceases to produce any precipitate: the pre- 

 cipitate should then be suffered to subside during the time of 

 twenty. four hours, in a vessel accurately closed ; after which the 

 mixture being filtered, and the precipitate dried and weighed, the 

 operator may proceed to examine it by the known methods. In 

 this manner the nature of the substance will be clearly ascertained 

 on which the re-agent has acted, and the cause of the decomposi- 

 tion may consequently be inferred. A certain order may be fol- 

 lowed in these operations, by mixing the waters first with such 

 substances as stand least capable of altering them, and afterwards 

 passing to other substances capable of producing changes more va- 

 ried and difficult to explain. The following method is that which 

 Fourcroy commonly uses in this kind of analysis. After having exa- 

 mined the taste, the colour, the weight, and all the other physical 

 properties of a mineral water, he pours four pounds of lime water 

 on an equal quantity of the fluid ; if no precipitate is made in 

 twenty-four hours, he is sure that the water contains neither discn- 

 a r ed carbonic acid nor alkaline carbonat, nor earthy salts with 



C5 O * 



the base of aluminous earth or magnesia, nor metallic salts. But if 

 a precipitate be formed, he filters the mixture, and examines the 

 chemical properties of the deposited substance ; if it has no taste, 

 if it be insoluble in water, or effervesces with acids, or forms an 

 insipid and almost insoluble salt by the addition of sulphuric acid, 

 lie concludes that it is chalk, and that the lime water has acted 

 only on the carbonic acid dissolved in the water. If, on the con- 

 trary, it is small in quantity, and subsides very slowly ; if it do not 

 effervesce, and affords with the sulphuric acid a styptic salt, or a 

 bitter and very soluble salt, it is formed by magnesia or aluminous 

 earth, and often by both. 



After Ihe exumiuatiou by lime water, Fourcroy pours on four 



