2. 72 nitrous gas, 924 per cent. = 664 real + 5 azote. 53 ammonia, 99 per cent. = 521/ 125 67.5 fired. + azote. 63 washed, 1 or 2 hydrogen, found by adding a little hydrogen, and exploding with oxygen. Here we have 2 hydrogen and 6 azote to subtract, and there will remain 55 azote generated from the nitrous gas and the ammonia. Estimating the effective nitrous gas at 66, the following explanation many be given: 66 nit. gas = 30 azote+ 36 oxygen. 51 am. gas 26/ 561 + 66 hyd. (= 64 [= 32 oxy.] + 2). The other hypothesis would also afford an easy solution; but we must admit that no nitrous acid is formed, and that part of the ammonia escapes combustion. Thus 66 nitrous gas = 33 azote + 33 oxygen. 45 am. gas = 221 + 67 hydrogen. 55 azote, and 14 surplus hydrogen. 3. 78 nitrous gas, 92 per cent. = 72 real + 6 azote. 28 ammoniacal gas, 99 per cent. 106 60 fired, muddy. 601 washed, 81 oxygen. Here we find 46 azote generated from the nitrous gas and ammonia, which may be explained thus: 72 nitrous gas = 33 azote + 39 oxygen. 31 ammo.gas = 164 491 + 40 hydrogen. 3 azote+ 10 oxygen = nitric acid. 46 An explanation on the other system might be as under : 72 nit. gas = 26 azote + 36 oxygen (= 191⁄2 + 8 + 81). 26 am.gas = 13 +39 hydrogen (19 oxygen). It is clear, therefore, that experiments with mixtures of nitrous gas and ammonia should be made with an excess of ammonia, if they are intended to decide between the two theories. ARTICLE III. A General Formula for the Analysis of Mineral Waters. THE analysis of mineral waters has always been considered as a difficult operation. Numerous methods are employed to discover their ingredients, and estimate their quantities, many of which are liable to errors. This diversity of method itself is a source of discordant results; and to those not familiar with such researches, it presents the difficulty often of determining what process is best adapted to discover a particular composition. Hence the advantage of a general formula, if this could be given, applicable to the analysis of all waters. The views which have been stated in the papers connected with this subject, which I have had the honour of submitting to the Society, have suggested a method which appears to me to admit of very general application, and to be simple, not difficult of execution, nor liable to any sources of error but what may be easily obviated. The principles on which this method is founded, and the details of the process itself, form the subject of the following observations. Two methods of analysis have been employed for discovering the composition of mineral waters-what may be called the direct method, in which, by evaporation, aided by the subsequent application of solvents, or sometimes by precipitants, certain compound salts are obtained; and what may be called the indirect method, in which, by the use of re-agents, the principles of these salts, that is, the acids and bases of which they are formed, are discovered, and their quantities estimated, whence the particular salts, and their proportions, may be inferred. Chemists have always considered the former of these methods as affording the most certain and essential information: they have not neglected the latter; but they have usually employed it as subordinate to the other. The salts procured by evaporation have been uniformly considered as the real ingredients, and nothing more was required, therefore, it was imagined, for the accuracy of the analysis, than the obtaining them pure, and estimating their quantities with precision. On the contrary, in obtaining the elements merely, no information, it was believed, was gained with regard to the real composition; for it still remained to be determined in what mode they were combined; and this, it was supposed, could be inferred * From the Transactions of the Royal Society of Edinburgh, vol. viii. p. 259, only from the compounds actually obtained. This method, therefore, when employed with a view to estimate quantities, has been had recourse to only to obviate particular difficulties attending the execution of the other, or to give greater accuracy to the proportions, or, at farthest, when the composition is very simple, consisting chiefly of one genus of salts. Another circumstance contributed to lead to a preference of the direct mode of analysis-the uncertainty attending the determination of the proportions of the elements of compound salts. This uncertainty was such, that, even from the most exact determination of the absolute quantities of the acids and bases existing in a mineral water, it would have been difficult, or nearly impracticable, to assign the precise composition and the real proportions of the compound salts; and hence the necessity of employing the direct method of obtaining them. The present state of the science leads to other views. If the conclusion were just, that the salts obtained by evaporation, or any analogous process from a mineral water, are its real ingredients, no doubt could remain of the superiority of the direct method of analysis, and even of the absolute necessity of employing it. But no illustrations, I believe, are required to prove that this conclusion is not necessarily true. The concentration by the evaporation must in many cases change the state of combination, and the salts obtained are hence frequently products of the operation, not original ingredients. Whether they are so or not, and what the real composition is, are to be determined on other grounds than on their being actually obtained; and no more information is gained, therefore, with regard to that composition, by their being procured, than by their elements being discovered; for when these are known, and their quantities are determined, we can, according to the principle from which the actual modes of combination are inferred, whatever this may be, assign with equal facility the quantities of the binary compounds they form. The accuracy with which the proportions of the constituent principles of the greater number of the compound salts are now determined enables us also to do this with as much precision as by obtaining the compounds themselves; and if any error should exist in the estimation of these proportions, the prosecution of these researches could not fail soon to discover it. The mode of determining the composition of a mineral water, by discovering the acids and bases which it contains, admits, in general, of greater facility of execution, and more accuracy, than the mode of determining it by obtaining insulated the compound salts. Nothing is more difficult than to effect the entire separation of salts by crystallization, aided even by the usual methods of the action of alcohol, either as a solvent or a precipitant, or by the action of water as a solvent at different temperatures; in many cases it cannot be completely attained, and the analysis must be deficient in accuracy. No such difficulty is attached to the other method. The principles being discovered, and their quantities estimated in general from their precipitation in insoluble compounds, their entire separation is easily effected. Nothing is easier, for example, than to estimate the total quantity of sulphuric acid by precipitation by barytes, or of lime by precipitation by oxalic acid. And this method has one peculiar advantage with regard to accuracy, that if any error is committed in the estimation of any of the principles, it is discovered in the subsequent step of inferring the binary combinations, since, if all the elements do not bear that due proportion to each other which is necessary to produce the state of neutralization, the excess or deficiency becomes apparent, and of course the error is detected. The indirect method, then, has every advantage over the other, both in accuracy and facility of execution. Another advantage is derived from these views, if they are just, that of precluding the discussion of questions which otherwise fall to be considered, and which must often be of difficult determination, if they are even capable of being determined. From the state of combination being liable to be influenced by evaporation, or any other analytic operation by which the salts existing in a mineral water are attempted to be procured, discordant results will often be obtained, according to the methods employed; the propor tions at least will be different, and sometimes even products will be found by one method which are not by another. In a water which is of complicated composition, this will more peculiarly be the case. The Cheltenham waters, for example, have, in different analyses, afforded results considerably different; and, on the supposition of the salts procured being the real ingredients, this diversity must be ascribed to inaccuracy, and ample room for discussion with regard to this is introduced. In like manner, it has often been a subject of controversy whether sea-water contains sulphate of soda with sulphate of magnesia. All such discussions, however, are superfluous. The salts procured are not necessarily the real ingredients, but in part, at least, are products of the operation, liable, therefore, to be obtained or not, or to be obtained in different proportions, according to the method employed. And all that can be done with precision is to estimate the elements, and then to exhibit their binary combinations according to whatever may be the most probable view of the real composition. The process I have to state, conformable to these views, is essentially the same as that which I employed in the analysis of sea-water in a preceding memoir; and it was the consideration of the advantages belonging to it that has led me to propose it, with the necessary modifications, as one of general application. Mineral waters have been arranged under the four classes of carbonated, sulphureous, chalybeate, and saline. But all of them are either saline, or may be reduced under this division. From waters of the first class, the carbonic acid which is in excess is expelled by heat, and its quantity is estimated. Sulphureted hydrogen is in like manner expelled or decomposed; and iron may be detected by its particular tests, and removed by appropriate methods. In all these cases the water remains, with any saline impregnation which it has, and of course is essentially the same in the subsequent steps of its analysis as a water purely saline; the precaution only being observed of these principles being removed, and of no new ingredient being introduced by the methods employed. The salts usually contained in mineral waters are carbonates, sulphates, and muriates, of lime, of magnesia, and of soda. In proceeding to the analysis, a general knowledge is of course first to be gained of the probable composition by the application of the usual tests; the presence of sulphuric and carbonic acids being detected by nitrate of barytes, of muriatic acid by nitrate of silver, of lime by oxalic acid, of magnesia by lime-water or ammonia, and of any alkaline neutral salt by evaporation. It will also be of advantage to obtain the products of evaporation, and ascertain their quantities, without any minute attention to precision, the object being merely, by these previous steps, to facilitate the more accurate analysis. Supposing this to be done, and supposing the composition of the water to be of the most complicated kind, that is, that by the indications from tests, or by evaporation, it has afforded carbonates, sulphates, and muriates of lime, magnesia, and soda, the following is the general process to be followed to ascertain the ingredients, and their proportions. Reduce the water by evaporation, as far as can be done without occasioning any sensible precipitation or crystallization; this, by the concentration, rendering the operation of the re-agents to be employed more certain and complete. It also removes any free carbonic acid. Add to the water thus concentrated a saturated solution of muriate of barytes, as long as any precipitation is produced, taking care to avoid adding an excess. By a previous experiment, let it be ascertained whether this precipitate effervesces or not with diluted muriatic acid, and whether it is entirely dissolved. If it is, the precipitate is of course carbonate of barytes, the weight of which, when it is dried, gives the quantity of carbonic acid; 100 grains containing 22 of acid. If it do not effervesce, it is sulphate of barytes, the weight of which, in like manner, gives the quantity of sulphuric acid; 100 grains, dried at a low red heat, containing 34 of acid. If it effervesce, and is partially dissolved, it consists both of carbonate and sulphate. To ascertain the proportions of these, let the precipitate be dried at a heat a little inferior to redness, and weighed; then submit it to the action of dilute muriatic acid; after this wash it with water, and dry it by a similar heat, its weight will give the quantity of sulphate, and the loss of weight that of carbonate of barytes. By this operation the carbonic and sulphuric acids are entirely removed, and the whole salts in the water are converted into mu |