some of the metallic oxides possess of separating the oxygen is curious.When these are added to it, the oxygen flies off with a sudden explosion: and, what is more, the oxygen of the oxide itself is liberated along with it, and the metal is reduced to a state of purity. Another singular fact is, that even the pure metal, when thrown into oxygenated water, effects a separation of the oxygen. In order to account for such an agency in a substance which does not enter, in the meantime, into any new chemical state, M. Thenard sagaciously suggests that the agency of the metal must be of an electrical nature. On this point, room is left for farther research.

A question has been raised, whether in the liquid oxygenated acids the oxygen is in union with the acids, or merely with the water? If the latter, the force of the argument already stated with regard to chlorine will be weakened, because the new compound, so different from chlorine, will come to be viewed not as an oxygenated muriatic acid, but muriatic acid in combination with oxygenated water. As an argument for supposing that the oxygen is really in union with the acid, it has been observed that simple water does not retain the oxygen so powerfully as the liquid acids do. But the force of this fact is diminished by another which has been discovered, viz. that various other impregnations, such as sugar and gum, also impart to water the property of retaining the combined oxygen with greater power.

Oxygenated water has been represented as possessed of a property capable of being turned to good practical account, viz. that of removing the dark colour induced on white lead by sulphureted hydrogen, which in many cases spoils the effect of old

paintings, and the oxygenated water does not in general injure those other colours with which the white lead is in contact on the canvas. It is said, however, that the same property is possessed also by chlorine, a substance much more easily procured.

CONSTITUTION AND ANALYSIS OF MINERAL WATERS.

Chemistry, in some of the improvements which it has recently undergone, has acquired a more complicated aspect than it previously wore, but in others it has been much simplified. In both cases, the science is extended, and its foundations fixed in a more satisfactory manner. The composition of mineral waters has always been an object of great interest to the chemist as well as to the physician. This has been manifested by the laborious manipulations which have been employed in the analysis. These have been multiplied by the difficulty of the subject, and they have in general tended to display in the end an uncertainty which appeared to be inseparable from it. In the midst of much doubt and disappointment, it is pleasing to find a ray of light thrown on their composition, which tends in one respect to simplify our views and abridge our labours, by shewing us at what point an uncertainty commences which no labour is adequate to remove.

Dr Murray's analysis of the mine. ral waters of Dunblane has led him to these improved views, which are unfolded in the 7th and 8th volumes of the Transactions of the Royal Society of Edinburgh at full length, in three Memoirs, entitled, "An Analysis of the Mineral Waters of Dunblane;"—" An Analysis of Sea-Wa

ter;" and "A general Formula for the Analysis of Mineral Waters;" all of them containing important information, both on general principles and on the details of manipulation. It is only a statement of the improved principles and general modes thus introduced that we can propose now to give, which will be most advantageously done in the order in which they are laid down, and in which they seem to have occurred to this chemist.

The water of Dunblane shewed, in the usual preliminary trials, that it consisted of neutral salts, composed of sulphuric and muriatic acids, lime, a minute portion of iron, and probably soda, though the presence of this last ingredient is less easily substantiated by trials of that preliminary kind. Muriates of soda and lime, with a smaller portion of a sulphate, were presumed to be the neutral salts by which it was impregnated; and the usual method of ascertaining the individual salts, by evaporation and crystallization, was resorted to.When an English pint was evaporated, 47 grains of a solid residue were left. This, when dried and then exposed, deliquesced from the presence of the muriate of lime, the muriate of soda remaining crystallized. These ingredients were more completely separated by means of alcohol, which dissolved the muriate of lime, and left the muriate of soda in the state of crystals; and, though such separation was not perfect in the first instance, it was completed by means of a repetition of the processes of solution and crystallization. The quantity of the muriate of lime was not only ascertained by driving off the alcohol which dissolved it, and weighing the solid matter that was left, but by determining the quantity of sulphuric acid required to decompose that salt, and

neutralize the base. From the quantity of sulphate of lime formed, that of the muriate of lime was calculated on the principles of chemical equivalents.-20.5 grains of sulphate of lime were obtained, leaving 16.7 of dry muriate of lime. The matter undissolved by the alcohol amounted to 28.5 grains. This matter was found to be all soluble in distilled water, except 2.4, and of this .5 were found to be carbonate of lime, and nearly .2 sulphate; but, from the quantity of sulphuric acid found by testing with a barytic salt, there were altogether 2.9 of sulphate of lime, provided the whole of that acid which was present existed in a state of combination with lime. He confirmed the accuracy of the results, by executing an analysis by a different method, which gave in a pint of the water,

This water has a purgative quality, which must arise from its impregnation; yet the muriate of lime is not known to possess that power, and muriate of soda only in a very slight degree. This was an exemplification of a well-established general fact, that the powers of mineral waters are often much greater than can be anticipated from the nature and quantity of their ingredients; and that the ac tion of saline substances is increased, and considerably modified, when they are in a state of great dilution.

This paper contains also an analysis of the water of Pitcaithly, affording the following results, as the ingredients of an English pint.

The observations which the author makes on the general question,-in what state do all the saline ingredients exist in a mineral water?-are of great importance. The different acids and bases may either be supposed to exist in a state of simultaneous combination, the whole acids being neutralized by the whole bases; or, as forming a mixture of different neutral salts. The latter opinion is embraced by him as the most probable of the two: Yet he conceives that the neutral salts, existing in the water, may not be the same with those which are evolved by the process of evaporation of crystallization, because the state of combination is liable to be modified by the analytic operations themselves. For example, when muriate of soda, muriate of lime, and sulphate of lime, were obtained in the quantities which we have stated from the Dunblane water, it is possible that the sulphate of lime may have been a product of the operation, and not an original ingredient. The sulphuric acid may exist rather in the state of sulphate of soda, and when, in the progress of the evaporation, the liquor becomes concentrated, this salt may act on a portion of the muriate of lime, and by mutual decomposition form corresponding portions of muriate of soda and sulphate of lime.

This is not a question of mere speculation, but may sometimes throw light on the properties of mineral waters. For example, in the present instance, sulphate of lime is a sub

stance apparently inert in its relation to the living system. If it exist, therefore, as such in the water, it can contribute nothing to its efficacy. But in the other state of combination which is supposed, both the quantity of muriate of lime, the active ingredient, will be greater, and the presence of sulphate of soda will in part account much better for the purgative operation which the water exerts. The question does not admit of being determined by direct experiment, as we know not when a neutral salt is merely separated from a solvent, and when it is formed in the operation. Nor does its separation by alcohol afford an unambiguous demonstration, as the alcohol may operate by acting on the water, and diminishing its solvent power by withdrawing it from the dissolved substance; thus leaving room for the force of cohesion to act in determining the combination of those ingredients which form the least soluble compound. One presumptive fact, however, was evolved by the author's experiments. He added to different portions of the water (four ounces each) 5, 10, 15, 20, and 30 grains of sulphate of soda. In the greater number of those proportions, the quantity of sulphate of soda was more than sufficient to convert the whole muriate of lime in the water to sulphate; and, according to the known solubility of this salt, the quantity of water was not sufficient to retain it all dissolved. Another result which he obtained was, that when he added a small portion of sulphate of soda, the quantity of sulphate of lime obtained was increased. When ten grains of the crystallized sulphate of soda are added to a pint of the water, four grains, or double the quantity of sulphate of lime are obtained; proving that both muriate of soda and sulphate of lime are liable to be formed in the progress of the

evaporation. Though the conclusion is not thus absolutely established, that the sulphuric acid exists in this water in the state of sulphate of soda, it is greatly favoured by it, and is on the whole the most probable opinion. If it be admitted, the statement of the ingredients and their proportions must be altered; the sulphate of lime must be omitted; the sulphate of soda, though it cannot by any method be separated in that form, may have its quantity inferred from that of the sulphate of lime, which is formed by its acting on the muriate of lime. The sulphates of lime and of soda being nearly the same in weight, the quantity found of the one may nearly be substituted for that of the other, as inferred to be present, and the whole proportions will be:

principal interest of this view arises from its relation to the question, whether chemical analysis is capable of discovering the sources of the medicinal virtues of mineral waters?—which some have been disposed to decide in the negative, from the fact that analysis, in some instances, detects no ingredients of adequate activity to the effects which these waters are found to produce on the system. It has been always found difficult to account for the virtues of the celebrated Bath wa ter, the ingredients obtained from it possessing little activity, and the prin cipal ones none at all. An English pint of it contains, along with a slight impregnation of carbonic acid, nine grains of sulphate of lime, three grains of muriate of soda, three grains of sulphate of soda, eight-tenths of a grain of carbonate of lime, one-fifth of a grain of silica, and one-twentieth of a grain of oxide of iron.-From these no medicinal operation of any importance could be expected: they are either altogether inert, or in quantities so extremely minute as to be incapable of producing any sensible effect in the dose in which the water is taken. Yet their virtues are established by sufficient practical evidence, and also their injurious effects when certain precautions in the use of them are neglected. To account for these, however, various hypotheses have been proposed.-It has been maintained that substances given in small doses, in a state of great dilution, may, from this dilution, produce more effect on the general system than the quantity given would lead us to expect. It is also supposed, that the temperature of the water may have some influence, particularly by favouring the action of the iron. Something has been ascribed to the nitrogen gas rising through the water, or the siliceous earth, of which one pint contains a grain. All this is unsatisfactory. It is not easy