CATARACTS, AND INUNDATIONS. 



sides of the moistened bladder alter and decompose the elastic fluid 

 obtained. It is scarcely necessary to remark, that the phenomena 

 exhibited by the water, during the escape of the gas, must be 

 carefully examined, and that a less quantity of water may be 

 exposed to distillation, in proportion as its taste and sparkling indu 

 cate that it contains a larger quantity of gas, 



Such is the method recommended by modern chemists to obtain 

 the elastic fluids combined with waters : It must be observed, I. 

 That this process cannot be depended on, with regard to acidulous 

 waters, unless the pressure of the atmosphere, and the state of com- 

 pression of the elastic fluid under the glass vessels be more accu 

 rately accounted foi : and as this is not easily done, the absorption 

 of carbonic acid by lime water, proposed by Gioanetti, appears to 

 be preferable. 2. Though it has been recommended by Bergman 

 to obtain sulphurated hydrogen gas from sulphureous waters, it 

 does not answer, because the heat of ebullition decomposes the gas, 

 and it is likewise decomposed by the mercury, which is converted 

 into etbiops, as soon as it comes in contact with this elastic fluid: 

 for this reason, litharge should be used to absorb this gas in the 

 cold, and to deprive sulphureous waters of their sulphur. 



The Examination of Mineral Waters by Evaporation. 

 Evaporation is generally considered as the most certain method of 

 obtaining all the principles of mineral waters. We have before ob- 

 served, ;ni(i here repeat, from various well conducted experiments, 

 that long continued ebullition may decompose saline matters dis 

 solved in water, and for that reason we have advised the exami- 

 nation of them by re agents, employed in greater proportions ; yet 

 evaporation may afford much information, when used, together 

 with the analysis by re-agents, which ought always to be considered 

 as one of the principal methods of examining waters. 



The intention of evaporation being to collect the fixed principles 

 contained in a mineral water, it is obvious, that in order td*know 

 the nature and proportion of these principles, a considerable quan- 

 tity of the water must be evaporated, and so much the more, in pro- 

 portion as the principles appear to exist in smaller quantities. 

 When the water is thought to contain a large quantity of saline mat- 

 ter, about twenty pounds must be evaporated ; if, on the contrary, 

 it appears to hold but a very small quantity in solution, it will be ne. 

 cessary to evaporate a much larger quantity. It is sometimes re* 



