nessee line. The valley of the stream is, at the well, narrow, and is deeply set in the Cumberland table-land; it cuts through the Coal-measures and into the top part of the Mountain limestone, exposing about 50 feet of the latter. The Mountain limestone is therefore much depressed at this point. The well is sunk near the river, and is less than 200 feet deep. It was bored, about 1825, for salt water. At its greatest depth, a reservoir of oil was struck, from which so much petroleum flowed as to lead to the abandonment of the boring as a salt well. For several years after petroleum was gathered at this point for medicinal purposes. How much petroleum issued from this boring. it is now impossible to tell. I give it simply as a good example of an oil reservoir actually tapped in the Mountain limestone. 2d. In the Siliceous group. There are several examples in this formation of reservoirs reached by boring. At b in the section the geological (not geographical) place of the "Porter well" in Allen county, Kentucky, is represented. This well is located on Bay's Fork of Big Barren, on a line between Scottsville and Bowling Green, and about seven miles from the former place and eighteen from the latter. This reservoir was tapped, some time in January of this year, at the moderate depth of 55 feet. It yielded for a number of days, by pumping, about 400 barrels of oil and strong brine per day, half of which was oil. At the time of my visit, Feb. 13th, it had produced altogether about 1000 barrels of petroleum, but was not then doing well.

In the southern part of Overton county, Tennessee, on Spring creek, is another example. Here a reservoir was struck which yielded heavy oil, but how much I am not informed.

3d. In the Black Slate. On Boyd's creek, near Glasgow, Kentucky, is a group of half a dozen wells or more. Their position is shown by the heavy vertical lines at c. met with oil in the Black Slate.

One or two of these

4th. In the Upper Silurian. All of the Boyd's creek wells start in the Siliceous group, most of them pass through the Black Slate and terminate in this group. Taking all the wells, they vary in depth from 60 to 250 feet, averaging about 130 feet. So it was at least at the time of my visit. One of them was, and may be now, a flowing well, having yielded for many months nearly or quite 30 barrels of oil per day. One or two of these borings may reach the next group of limestones below. In fact practically, and possibly in reality, the rocks may be united with the Nashville group.

5th. In the Nashville group. This group has furnished the most and the largest reservoirs. The geological and topographical place of a number of borings, which have tapped oil reservoirs, on the Cumberland and Obey rivers, and on their tributaries, both in Kentucky and Tennessee, is shown by the heavy

short lines at d, d. The old "American oil well" near Burksville, originally bored for salt water, may be taken as an example. This, from top to bottom, is within the Nashville group. Its mouth is not far from 40 feet below the level of the Black Slate. At the depth of about 175 feet this boring tapped an oil reservoir, from which flowed out, at a minimum estimate, 50,000 barrels of oil. The recently bored Crocus creek well, which has yielded up to this time not far from 30,000 barrels, is another example. Other examples might be given, but these are sufficient. A great number of wells will be sunk in this forma tion during the present year.

6th. In the Trenton limestones. Some boring has been done in this series, but as yet no repositories of any note have been discovered, at least in Tennessee.

Nashville, Tenn., March 19th, 1866.

ART. XIX.-Analyses of some minerals from the Emery mine of Chester, Mass.; communicated by Dr. C. T. JACKSON. (From a letter to one of the Editors.)

1. Andesine. The emery vein enlarges as it goes in, and from four feet has already widened to seven feet eight inches of solid emery of the best quality. The adit now is extended 260 feet.. The portion of rock originally mistaken by me for granular quartzite, and called Indianite by Shepard, proves on analysis to be Andesine, although it is harder than stated in the books, scratching quartz crystal readily. It is associated with crystals of black tourmaline. It is very compact, fine granular in texture, with a conchoidal splintery fracture, and has G. = 2.586, H.75; the color slightly greenish white. I obtained for its composition,

1.

2.

In No. 2 there was a trace of oxyd of iron not weighable. 2. Analysis of Margarite, by JOHN C. JACKSON.-The margarite of Chester has, G. = 3.03, H. = 3.5-4. The analysis afforded:

3. Diaspore. The first of the following analyses of diaspore was made by my son, John C. Jackson. I was in hopes he would have had time to repeat the work and determine the alumina directly, an accident having damaged that part of his analysis so that he can give it only by difference. In my analysis of the same mineral the ingredients were all directly determined. The quantity analyzed at a time was 10 grains; two analyses were made. The diaspore is in prismatic crystals which contain microscopic crystals of Brookite. H. 7 nearly, scratching quartz distinctly but feebly. G. 3:39. Analyses:

Water,
Alumina,

Oxyds titanium and iron,

Sesquioxyd of iron and oxyd titanium,

=

The diaspore occurs in both the North and South Mountains, associated with emery and chloritoid. It exists both in bladed striated crystals, and in small prisms of considerable length, sometimes an inch or more long. Only the microscopic crystals present perfectly defined forms.

Chloritoid.-Ten grains of the chloritoid were selected for the analysis, as pure as possible, but it still contained microscopic particles of magnetic iron ore and perhaps of emery.

The results of my analyses are as follows. The second column contains these results as they would be if half the oxyd of iron is protoxyd:

If I can procure crystals free from any admixture I shall reanalyze it. It is plain that if the mineral is chlorite the magnesia is replaced by protoxyd of iron. It differs less from chloritoid but more from masonite, which by my analysis, published in my Report on the Geology of Rhode Island, contains 6 pr. ct. of oxyd of manganese and 32.20 of silica. The following is my analysis of masonite: (From analyses made in 1839 and published in 1840; Geol. of R. I., page 88, Prov., R. I., 1840. The analysis was repeated several times, and this is a mean of a number of carefully made analyses by myself on 25 and 50 grain lots.) Water, Silica Alumina,

4.000

33.200

29.000

0 240 25.924

6000

99.374

ART. XX.-On the detection of Iodine; by M. Carey Lea.

WHERE iodine exists in the form of hydriodic acid, or the iodid of a base, two methods are commonly employed to put it into a condition to be detected by the starch test. One of these is by the action of nitric acid, the other by chlorine or bromine water. The latter is the more delicate, but has the disadvantage that if the chlorine or bromine be added in excess, the reaction is missed.

It occurred to me while engaged in testing for iodine, that the facility with which that body is eliminated from its hydrogen and metallic combinations by chromic acid would make the latter substance a valuable means of bringing about the starch reaction, and a few experiments completely confirmed this view.

If, for example, we take an extremely dilute solution of iodid of potassium, such that the addition of nitric acid and starch produces no perceptible effect, the further addition of a single drop of very dilute solution of bichromate of potash will instantly bring about the characteristic reaction.

When chlorhydric acid is substituted for nitric, the effect of the bichromate is (as was to be expected) still more marked. The test has then the full delicacy at least of the chlorine test, with this great advantage, that an excess of the reagent does not prevent the reaction.

As to the delicacy of this test, the following observations were made.

With solutions of iodid of potassium up to one hundred thousandth (1: 100,000) the precipitate was abundant, becoming less blue and more tawny as the dilution increased. Beyond this poiut the distinctness rapidly fell off. The indications were observable at one-four-hundred-thousandth. With a solution of one-eight hundred-thousandth it was doubtful whether any effect was evident though still it was thought that a darkening was produced.

The experiment can be made in two ways, according to the result desired.

If it is wished to observe the effect of the chromic acid in increasing the delicacy of the indication, add the acid and starch to the very dilute solution of iodid, and then when the extreme dilution is such that no reaction appears, a drop of solution of bichromate instantly produces it.

But in employing the reagent in the search for iodine, add the starch to the liquid to be tested, stir it up, add a drop of dilute solution of bichromate, enough to communicate a pale yellow color, and finally add a few drops of chlorhydric acid. The test is then the production of the characteristic precipitate,

or in case of great dilution, approaching to a half-millionth, merely a tawny shade given to the solution.

It seems scarcely necessary to say that if a very great excess of acid is used, and too much bichromate, the starch may be made to reduce the bichromate. Even this, however, cannot deceive, for a bluish-green solution is thereby produced, whereas the indications of iodid are in the order of their strength: blue precipitate, tawny precipitate, tawny solution. Unless in the case of very exceptional dilution above spoken of, a well marked blue precipitate is always obtained.

The examination of the delicacy of the reaction with very dilute solutions was made at a temperature of 65° F. or thereabouts. This fact requires to be taken into account, as according to some experiments of Fresenius to be found in the Jahresbericht for 1857, the delicacy of the starch test increases as the temperature falls, so that at 0° C. a fainter trace can be rendered evident than at 12° C., and so on: the difference is asserted to be material. Fresenius's experiments were made with sulphuric acid and hyponitric acid, and the delicacy of the reaction obtained by him at corresponding temperatures seems to fall a little short of the above.

SCIENTIFIC INTELLIGENCE.

I. CHEMISTRY AND PHYSICS.

1. On the preparation of Hydrofluoric Acid; by W. P. DEXTER.Few chemists have at their disposal a distillatory apparatus of platinum, and the cryolite from which the purest hydrofluoric acid is prepared; and the shape commonly given to the dome of platinum retorts is such as to allow matter which may be projected upon it to flow down the neck into the receiver. The acid made from fluor spar in such a retort I have found to contain sulphate of lime. A simple remedy for this defect would be to fix in the dome a perforated disc, or ring, over the aperture of which another disc of less diameter, but larger than this aperture, is supported by three strips of platinum rivetted to the ring, both being made of silver platinum foil.

A dome of platinum attached to a leaden vessel seems to me a halfway measure, combining the disadvantages attending the use of both metals.

To those who are not in possession of an apparatus of platinum, I can recommend from experience the following comparatively inexpensive arrangement.

It consists of the ordinary leaden bore, (mine is 6" high by 3" internal diameter,) made of a piece of lead pipe into which a bottom of lead is cast, and provided near the top with a small and short tube for the escape of the gas. The tube must incline slightly from the retort up