According to the different opinions which are enter tained, with respect to the stale of combination of the ingredients, different methods have been recommended for ascertaining the compounds which mineral waters contain. The First of these is by the slow evaporation of the fluid.
By slowly et a,. _rating the water, the different saline substances may be obtained separately. For this pur pose, the evaporation is continued till a pellicle appear on the surface ; the liquid is then allowed to cool slow ly ; by this the earthy carbonates will be deposited. After these are removed, by a farther evaporation and cooling, the sulphate of lime will be separated. The alkaline neutral salts, and the sulphate of magnesia, will be deposited after the next evaporation. The muriates of lime and magnesia will remain, and will be obtained by evaporation to dryness.
If the water contain carbonate of iron, it must, after having been evaporated to a certain extent, be exposed to the air, by which the iron passes to a higher state of oxidation, and is no longer soluble in the acid ; it is therefore precipitated. The earthy carbonates are like wise separated by this means. After these have been deposited, the fluid may be evaporated to dryness, and a small quantity of water poured on the residue, by which sonic of the salts will be dissolved, and the others will be left. Sometimes the water is evaporated to dryness, and the residue is exposed to the air, by which the de liquescent salts, as the muliates of lime and magnesia, absorb moisture, and are dissolved. What is left undis solved, may be afterwards subjected to the action of wa ter. Occasionally, after evaporating the fluid to dry ness, the residue is subjected to the action of successive portions of water, by which the salts are taken up in the order of their solubility.
The different quantities of saline substances, thus ob tained by these various methods, must be dissolved in separate portions of water, that by slow evaporation the salts which are mixed may be separated.
Another method of ascertaining the nature of the salts in mineral waters, is by means of alcohol. Some of the salts contained in mineral waters arc soluble, while others are insoluble in alcohol. By a particular
management, the different saline substances may be obtained, either in solution, or by deposition from the water.
When alcohol is added to water, containing saline matter, the attraction between the two fluids is so strong, that those salts which are insoluble in alcohol are separated from the water, and are deposited ; thus, if a mineral water be mixed with an equal quantity of alcohol, sulphate of lime, if present, will be precipi tated ; if more alcohol be added to the fluid, the sulphate cf soda will be separated ; by adding another quantity of alcohol, muriate of soda will be thrown down. This method of employing alcohol in the analysis of mineral waters, was first pointed out by Boulduc.
Lavoisier has recommended another way of using al cohol. For this purpose the mineral water is to be evaporated to dryness, and eight parts of alcohol pour ed on the residue, by which some of the salts only will be dissolved. By adding alcohol, diluted with a little water, to the undissolved matter, another portion of the saline substance is taken up. In this way, by using alco hol of different specific gravities successively, the diffe rent saline compounds may be obtained separately ; thus, when strong alcohol is poured on the residue of the eva poration of a mineral water, muliates of lime and mag nesia, if present, will be dissolved. By diluting the next portion of alcohol with a little water, muriate of soda will be taken up, the carbonates and sulphates be ing left.
Occasionally these two methods of employing alco hol are joined ; thus the mineral water is evaporated to dryness, and alcohol is poured on the residue, by which the muriatcs of lime and magnesia are dissolved. When the solution is completed, the fluid is filtered, and a small quantity of cold water is added to the un dissolved matter, by which more of the saline sub stance is taken up. What remains is then boiled in a large quantity of water; by the application of the tests to the alcoholic and watery solutions, the different substances which they contain will be discovered.