vessel containing the sulphureous water through which it bubbles in a brisk but not violent stream. The gas, more or less charged with sulphuretted hydrogen, is led into a third vessel containing either a solution of nitrate of silver to which ammonia has been added, or an alkaline solution of arsenious acid, to arrest the sulphuretted hydrogen. The former solution is greatly to be preferred where the mineral water is only feebly sulphureous. The sulphur thus precipitated is to be determined in the usual way. Suppose the mineral water to contain free hydrosulphuric acid together with sulphids say of potassium and magnesium, we may proceed as follows: 1. We determine for a given volume of the water the total amount of sulphur present by the use of chlorid of copper or nitrate of silver. 2. We subject an equal volume of the water to the hydrogen current until the escaping gas gives only the faintest trace of hydrosulphuric acid when the jet is received on a surface of white porcelain rendered moist by a mixture of nitrate of silver and ammonia. The mixed gas being passed into the silver or arsenious solution, gives a precipitate from which we determine the amount of free hydrosulphuric acid in the water. 3. We apply heat to the flask containing the sulphureous water which has been thus treated, so as to canse gentle boiling, at the same time supplying the upper space with hydrogen in a moderate but steady stream. It will be found that below the point of ebullition the issuing hydrogen will give scarcely a trace of hydrosulphuric acid, but as soon as the liquid begins to boil, the stream of vapor and hydrogen plainly shows the presence of this substance, then slowly evolved by the decomposition of the sulphid of magnesium or calcium. 4. We treat the remaining liquid with chlorid of copper, or the arsenious solution, to determine the sulphur of the alkaline sulphid which is the only sulphur compound left in the water. The sum of this and the sulphur of the free hydrosulphuric acid subtracted from the total quautity of sulphur gives that of the sulphid of magnesium. We find that a proportion of hydrosulphuric acid too small to be quantitatively determined by precipitation from the water itself can be ascertained by the use of the stream of hydrogen. It is only necessary to pass the gas which has been transmitted through the water into an ammoniacal solution of nitrate of silver in a long test tube or Liebig's bulb. By continuing the action for one or two hours we obtain a precipitate capable of being separated. When the water contains no sulphid of magnesium or cal cium, it is merely necessary, after determining the total amount of sulphur present, to boil the liquid in an atmosphere of hydrogen as long as the gas gives a distinct trace of SH by the tache on porcelain as before described; and then by precipitation to determine the quantity of sulphur in the alkaline sulphid of the remaining liquid. From what has been said it is obvious that the only practical objection to the process here proposed is the tardiness of the displacing action of the hydrogen gas; but considering the acknowledged imperfection of the methods in use, we think that it may be found worthy of adoption. Second. On the use of Carbonic Acid Gas in the analysis of mineral waters containing Sulphuretted Hydrogen. As might be inferred from its great absorbability by water, carbonic acid acts much more rapidly than hydrogen in separating hydrosulphuric acid from that liquid. To assure ourselves of this effect, we made several experiments with natural and artificial sulphureous waters, all of which led to the same result. The following example will suffice to show the efficiency and promptness of the displacing action of the carbonic acid. Twenty-five cubic inches of Blue Lick water contained in a narrow necked bottle, were subjected to the washing action of a brisk stream of carbonic acid gas previously purified by transmission through water. In fifteen minutes the liquid, tested by ammoniacal nitrate of silver, gave a scarcely discernible trace of hydrosulphuric acid, and in twenty minutes not a vestige of it could be detected by the same reagent. The rapidity and completeness of the separation are as striking as the ease with which the experiment can be made. When therefore a mineral water is known to contain sulphuretted hydrogen only in the free state, we would recommend as the simplest and most exact method for determining this ingredient, to pass through the liquid a stream of washed carbonic acid gas, and to arrest the hydrosulphuric acid, by conducting the current of mixed gas into an ammoniacal solution of nitrate of silver in a small flask or Liebig tube. The precipitated sulphuret being mingled with only a small volume of liquid, admits of more easy separation and determination than when formed in the usual way by adding a precipitant to a large mass of the mineral water. In the case of feebly sulphureous waters this method is we think greatly superior in accuracy as well as promptness to any of those in use. By operating on a considerable volume of the water, the flask or tube will furnish the precipitated sulphuret in sufficient amount for a quantitative determination in cases where in the ordinary way no separable precipitate would be obtained. As carbonic acid is capable of decomposing the sulphids contained in a mineral water giving rise to free hydrosulphuric acid, it cannot be employed for determining the quantity of the latter when associated in the water with a sulphid. In this case the stream of carbonic acid would carry with it the hydrosulphuric acid due to its reaction with the sulphids, as well as that existing ready formed in the liquid. For such a water, hydrogen gas used as above explained, is the proper displacing agent. ART. XXVII-On Changes of the Sea-Level effected by existing Physical Causes during stated periods of time; by Alfred TYLOR, F.G.S. (Concluded from page 32.) PART II. ALLUSIONS have already been made to the difficulty of proving whether or not the sea-level had been gradually elevated, because the rise of the waters would conceal the evidence of their former height except just at the mouths of rivers, where deposits of fluviatile alluvium might raise the land from time to time and keep it above the waves. The recent strata formed at a few such localities have been described by the best observers; and while there are appearances in several cases which might be to some extent explained by the supposition of a gradual rise of the sea-level, yet no proof could be obtained without the concurrent testimony of a much greater number of instances than have yet been brought forward. Sufficient information, it appears, exists to show that the quantity of alluvium in the deltas of such rivers as the Mississippi, Ganges and Po, is so enormous, that the accumulation must have occupied a period of time during which it would not be possible to conceive the sea-level stationary. Little progress could be made in an inquiry of this kind without clear views of the operations of rivers. The recent reports of engineers upon this subject supply an important link in the chain of evidence, aud enable us to understand the laws which govern the formation of alluvial plains along the lower parts of all river-courses. The diagram (fig. 8) represents a section of 600 miles of North America, through the alluvial plains and delta of the Mississippi,* together with a section of the Gulf of Mexico, from a point 100 miles east of the Balize to the continent of South America. The sea-bottom is marked from the soundings on the Admiralty Chart, and the depth of the Mississippi and its fluviatile deposit are inserted from statistics collected by Sir C. Lyell.† For a most valuable detailed description of the physical geography, &c. of the Mississippi and Ohio valley, see Mr. C. Ellet's paper, Smithsonian Contributions, vol. ii, 1851. See note, page 26. Head of Fig. 8.-Diagram showing depth of the Delta (supposed. 600 feet); area 14,000 square miles; height of the river above the sea-level 275 feet at *; depth of river, supposed 80 to 200 feet in this diagram; ditto of plains, supposed to average 264 feet; area, 16,000 square miles. Junction with River Ohio. a, a. Fluviatile st ata of the plains of the Mississippi; the slope of these plains is determined by measurement to be about 1 foot in 10,000 towards the sea. Fig. 9.-Transverse section of the Mississippi, where it is 1500 feet wide and 100 feet deep, running in the midst of an alluvial plain 50 miles wide. a, a. The level of water in the river during flood, which is 25 feet above the level of the distant marshes, m, m. c, c. The level of water in the dry season. b, b. Artificial banks or levees, 4 feet high. d, d. The banks and pl tins. m, m. Marshes, supplied with water by filtration from the river at all seasons of the year. The whole body of water in the river must be in motion, so that even in flood time only a small per-centage of the water and alluvium in the stream can escape over the banks. South America. SECOND SERIES, Vol. XVIII, No. 53.-Sept, 1854. 28 It will be seen that the level of the water in the Mississippi, near its junction with the Ohio, nearly 600 miles from the Gulf of Mexico, is 275 feet above that of the sea. The slope of the alluvial plains through which the river winds will therefore be less than 1 foot in 10,000. The hills bordering the valley of the Mississippi are cut through in several places by the river, thereby exposing good sections of their component strata, consisting of alluvial deposits thought to be much more ancient than those we are about to consider. An area of 16,000 square miles is occupied by the more modern alluvial formation between the head of the delta and the junction of the Ohio.* It is supposed to be, in the average, 264 feet deep, and is from 30 to 80 miles wide. The true delta extends over 14,000 square miles, occupying a frontage of 24 degrees on the coast-line of the Gulf of Mexico, and extends 180 miles inland. At its southern extremity its surface is hardly above the level of high tides, but it rises gradually as it passes inland, and at New Orleans is nearly 10 feet above the sea-level. A boring near Lake Pontchartain, of 600 feet, failed to penetrate the modern alluvium; and wherever excavations are made, the remains of trees are frequently found, apparently in the places where they grew, but now far below the sca-level. Sir Charles Lyell computes its average depth at 528 feet, and consequently nearly the whole of this modern deposit is below the sea-level, yet is supposed not to contain marine remains. The fall of the Mississippi during a course of 600 miles is shown by fig. 8; the depth of the channel varies from 80 to 200 feet until it approaches the Balize, where it shallows to 16 feet. The rise of the tide at this point is only 2 feet. The depth of the alluvial deposit below the river-channel is also indicated, together with the surface of the more aucient formation upon which the Mississippi has formed this great alluvial deposit, the bottom of which is now more than 500 feet below the present sea-level. Mr. Charles Ellet, Jun., in a Report to the American Secretary of War, January 29, 1851, communicates the information from which the diagrams figs. 1 and 2 are constructed. See p. 23. The theory of Mr. C. Ellet is, that the velocity of the stratum of fresh water (fig. 1) is communicated entirely to the underlying stratum, composed of salt water, partially to the next stratum 3, but not at all to stratum 4, which is stationary: stratum 5 is also marine, but it flows in an opposite direction to the rest, and restores the salt water which is carried away by the friction of the upper stratum, No. 1, against the suface of No. 2. It is supposed that the rapid increase of deposit at the bar, fig. 1, arises from stratum No. 5 carrying mud to that point, where its *Lyell's Second Visit to the United States, 1849, vol. ii, pp. 146-152, 155, 169, 194, 195, 203, 243, &c. |