188 SPRINGS, IUVERS, CANALS, LAKES, 



tation of many substances, which owe tbeir solubility to llie presence 

 of these volatile matters, likewise produces a re-action among'the other 

 fixed matters, whose properties are accordingly changed. The phe- 

 nomena of double decompositions which heat is capable of pro. 

 fJucing between compounds that remain unchanged in cold water, 

 cannot be estimated and allowed for, but in consequence of a long se- 

 ries of experiments not yet made. Without entering, therefore, more 

 fully into these considerations, it will be enough to observe, that 

 this assertion, whose truth is admitted by every chemist, suffi- 

 ciently shows, that evaporation is not entirely to be depended on. 

 Hence it becomes a question, whether there be any method of as. 

 certaitiitig the peculiar nature of substances dissolved in water with, 

 out having recourse to heat ; and whether the accurate results of the 

 numerous experiments of modern writers afford any process for cor. 

 reeling the error which might arise from evaporation. The follow- 

 ing pages extracted from a memoir communicated by M. Fourcroy 

 to the Royal Society of Medicine, will show, that very pure re- 

 agents used in a peculiar manner, may be of much greater use in 

 the analysis of mineral vtaters than has hitherto been thought. 



Among the considerable number of re-agents proposed for the 

 analysis of mineral waters, those which promise the most useful re- 

 sults are tincture of turnsole, syrup of violets, lime-water, pure and 

 caustic potash, caustic ammoniac, concentrated sulphuric acid, ni- 

 trous acid, prussiat of lime, gallic alkohol, or spirituous tincture 

 f>J ?ZH/-a//,y,the nitric solutions of mercury and of silver, paper co- 

 loured by the aqueous tincture of fernambouc, which becomes 

 blue by means of alkalis, the aqueous tincture of terra mcrita, 

 which the same salts convert to a brown red, the oxalic acid to ex. 

 liibit the smallest quantity of lime, and the inuriat of barytes to 

 ascertain the smallest possible quantity of sulphuric acid. 



The effects and use of these principal re-agents have been ex- 

 plained by all chemists, but they have not insisted on the necessity 

 of their state of purity. Before they are employed, it is of the ut- 

 most importance perfectly to ascertain their nature, in order to avoid 

 fallacious effects. Bergman has treated very amply of ihe altera- 

 tions they are capable of pruducing. This celebrated chemist 

 ailirms, that paper coloured with the tincture of turnsole becomes 

 of a deeper blue by alkalis ; but that it is not altered by the carbo. 

 nic acid. But as this colouring matter is useful chiefly to ascertain 



