WATER. 



different faline fubftances contained in a mineral water. 

 They muft of courfe be varied according to circumftances ; 

 but this, as well as the application of other methods, muft 

 depend upon the praftical knowledge and judgment of the 

 analyft. 



The principles, however, upon which many of the above 

 analytical procefles are founded, have been lately called in 

 queftion by Dr. Murray of Edinburgh, and we think very 

 juftly. That gentleman has endeavoured to (hew, that we 

 by no means arrive atajuft knowledge of the conftituents of 

 a mineral water by thefe procefles, and that many of the 

 compounds obtained by them are determined by the pro- 

 ceffes themfelves. The following quotation, from a paper 

 by Dr. Murray, entitled " A general Formula for the 

 Analyfis of Mineral Waters," in the eighth volume of the 

 Tranfaftions of the Royal Society of Edinburgh, will con- 

 vey a diflinft idea of his opinions and mode of reafoning 

 upon the fubjeft. 



Two methods of analyfis have been employed for dif- 

 covering the compofition of mineral waters, what may be 

 called the direH method, in which, by evaporation, aided by 

 the fubfequent application of folvents, or fometimes by 

 precipitants, certain compound falts are obtained ; and what 

 may be called the indireB method, in which, by the ufe of 

 reagents, the principles of thefe falts, and bafes of which 

 they are formed, are difcovered, and their quantities efti- 

 mated, whence the particular falts and their proportions 

 may be inferred. 



Chemifts have always confidered the former of thefe me- 

 thods as affording the moft certain and eflential information. 

 They have not negltfted the latter, but they have ufually 

 employed it as fubordinate to the other. The falts pro- 

 cured by evaporation have been uniformly confidered as the 

 real ingredients ; and nothing more was required, therefore, 

 it was imagined, for the accuracy of the analyfis, than the 

 obtaining them pure, and eftimating their quantities with 

 precifion. On the contrary, in obtaining the elements 

 merely, no information, it was believed, was gained with 

 regard to the real compofition ; for it ftill remained to be 

 determined in what mode they were combined : and this, it 

 was fuppoled, could be inferred only from the compounds 

 aftually obtained. This method, therefore, when employed 

 with a view to eftimate quantities, has been had recourfe to 

 only to obviate particular difficulties attending the execution 

 of the other, or to give greater accuracy to the propor- 

 tions, or, at furtheft, when the compofition is very fimple, 

 confdling chiefly of one genus of falls. 



Another circumftance contributed to lead to a preference 

 of the direft mode of analyfis, — the uncertainty attending 

 the determination of the proportions of the elements of the 

 compound f-lts. This uncertainty was fuch, that even 

 from the moft exaft determination of the abfolute quantities 

 of the acids and bafes exifting in a mineral water, it would 

 have been dilEcult, or nearly impracticable, to aflign the 

 precife compofition and the real proportions of the com- 

 pound falts : and hence the ncceflity of employing the direft 

 method of obtaining them. 



The prefent ftate of the fcience leads to other views. 



If the conclufion was juft, that the falts obtained by eva- 

 poration, or any analogous procefs from a mineral water, 

 are its real ingredients, no doubt could remain of the fu- 

 periority of the direcl method of analyfis, and even of the 

 abfolute neceflity of employing it. But no illuftrations, I 

 believe, are required to prove that this conclufion is not ne- 

 celTarily true. The concentration by the evaporation muft, in 

 many cafes, change the ftate of combination ; and the falts 

 obtained are hence frequently produfts of the operation, not 



Vol. XXXVIII. 



original ingredients. Whether they are fo or not, and what 

 the real compofition is, are to be determined on other 

 grounds than on their being aftually obtained ; and no more 

 information is gained, therefore, with regard to that com- 

 pofition, by their being procured, than by their elements 

 being difcovered; for when thefe are known, £ind their 

 quantities are determined, we can, according to the prin- 

 ciple from which the aftual modes of combination are in- 

 ferred, whatever this may be, aflign with equal facility the 

 quantities of the binary compounds they form. 



The accuracy with which the proportions of the confti- 

 tuent principles of the greater number of the compound falts 

 are now determined, enables us alfo to do this witli as much 

 precifion as by obtaining the compounds themfelves ; and if 

 any error fltould exift in the eftimation of their proportions, 

 the profecution of thefe refearches could not fail foon to 

 difcover it. 



The mode of determining the compofition of a mineral 

 water, by difcovering the acids and bafes which it contains, 

 admits in general of greater facility of execution, and more 

 accuracy, than the mode of determining by obtaining infu- 

 lated the compound falts. Nothing is more difficult than to 

 efFeft the entire feparation of falts by cryftallization, aided 

 even by the ufual methods of the aftion of alcohol, either as 

 a folvent or a precipitant, or by the aftion of water as a 

 folvent at different temperatures : in many cafes, it cannot 

 be completely attained, and the analyfis muft be deficient in 

 accuracy. No fuch difBculty is attached to the other me- 

 thod. The principles being difcovered, and their quantities 

 eftimated in general from their precipitation in infoluble 

 compounds, their entire feparation is eafily effefted. No- 

 thing is eafier, for example, than to eftimate the total 

 quantity of fulphuric acid by precipitation by barytes, or 

 of lime by precipitation with oxalic acid ; and this method 

 has one peculiar advantage with regard to accuracy, that if 

 any error is committed in the eftimation of any of the prin- 

 ciples, it is difcovered in the fubfequent ftep of inferring the 

 binary combinations : fince, if all the elements do not bear 

 that due proportion to each other, which is neceflary to 

 produce the ftate of neutralization, the excefs or deficiency 

 becomes apparent, and of courfe the error is detefted. 

 The indireft method, then, has every advantage over the 

 other, both in accuracy and facility of execution. 



Another advantage is derived from thefe views, if they 

 are juft, that of precluding the difcuflion of queftions, 

 which otherwife fall to be confidered, and which muft often 

 be of difficult determination, if they are even capable of 

 being determined. From the ftate of combination being 

 liable to be influenced by evaporation, or any other analytic 

 operation, by which the falts exifting in a mineral water are 

 attempted to be procured, difcordant refults will often be 

 obtained, according to the methods employed : the propor- 

 tions at leaft will be different, and fometimes even produfts 

 will be found by one method, which are not by another. 

 In a water which is of a compUcated compofition, this will 

 more peculiarly be the cafe. The Cheltenham waters, for 

 example, have in different analyfes afforded refults confider- 

 ably different : and on the fuppofition of the falts procured 

 being the real ingredients, this diverfity muft be afcribed to 

 inaccuracy ; and ample room for difcuflion with regard to 

 this is introduced. In like manner, it has often been a fub- 

 jeft of controverfy whether fea-water contains fulphate of 

 foda with fulphate of magnefia. All fuch difcuflions, how- 

 ever, are fuperfluous. The falts procured are not uecef- 

 farily the real ingredients, but in part, at leaft, are produfts 

 of the operation ; liable, therefore, to be obtained or not, 

 or to be obtained in different proportions, according to the 

 I) method 



