atacamite. The following is Mr. Tyler's account of his investigations.

"The specific gravity of a small piece of the mineral which I analyzed, was 43. It agreed in other physical characteristics with the description given in the Mineralogy.

On charcoal, the mineral swells, effervesces and melts at last to a globule of CuO. Held in the blue flame with the platinum forceps, it tinges it a bright green color. Heated in the closed tube it gives off sulphur, sulphurous acid and water. microcosmic salt it gives the copper reaction.

With

This mineral was dissolved in concentrated nitric acid. From the solution, copper was precipitated by means of sulphuretted hydrogen, and determined, by Rose's method, as Cu2S; the iron was precipitated with ammonia, and the lime with oxalate of ammonia.

To determine the sulphur, a separate portion of the substance was treated with fuming nitric acid; the sulphur which remained undissolved was filtered off, dried and weighed as such, and that which was oxydized to sulphuric acid was precipitated from the solution with chlorid of barium and weighed as sulphate of baryta.

1.0137 grm. of the mineral gave 8132 Cu S, containing 6444 Cu; 027 Fe2O3, containing 0189 Fe; 009 CaO.

8110 grm. gave 6437 Cu2S, containing 5140 Cu; and '0205 Fe 030143 Fe.

8749 grm. gave 0372 S and 8268 BaOSO3, containing 1135 S. Several trials to determine the loss by igniting gave from 15 to 20 per cent-nothing constant however. The amount of sulphur driven off, and the degree of oxydation which the copper assumes, appear to vary according to circumstances.

If now we consider the iron and lime as not essential, the formula will be CuS+CuO+HO.

I have considered one of the atoms of copper here as combined with oxygen; and have taken the difference necessary to make 100 as water, (or, what amounts to the same thing, have taken the water at one equivalent). The direct determination of the latter is in this case a difficult matter, and I have not the opportunity now of making it. That the above is the true composition of the mineral I think the following considerations show.

1st. The fact that sulphur is given off when the mineral is heated in a matrass proves the presence of CuS, not of Cu3S. This leaves an atom of Cu which can be combined only with oxygen.

2nd. The presence of CuO is indicated by the following reactions. The mineral tinges the blowpipe flame green gives off sulphurous acid in the closed tube: ammonia dissolves part of it when pulverized, to a deep blue liquid, and as CuS is insoluble in ammonia this must be CuO.

3d. All pure sulphurets of the metals hitherto described are anhydrous; the presence of water, therefore, in combination, and to such an extent as here, is a strong argument for considering the mineral partially an oxyd.

4th. There are exactly two equivalents of Cu present, and just enough excess of S above one equivalent to combine with the Fe and CaO. If now we consider the extra atom of Cu as combined with oxygen, there remain about nine per cent (8.61), which we are justified in regarding as the correct amount of water contained in the mineral.

3. Moronolite.-A description of this species will be found in the appendix to my Mineralogy. From the analyses here given it would appear to be nearly identical with the Gelbeisenerz found at Kolosoruk near Berlin, and analyzed by Rammelsberg, and in alum slate at Kirchspiel Modum, Norway, as analyzed by Scheerer (both referred to below by Mr. Tyler). All these substances are closely akin to the Jarosite of Breithaupt from Jaroso, Spain.1

Mr. Tyler gives the following as the result of his examinations. "The analysis was conducted in the usual way so far as the bases are concerned. To determine the amount of water, (which could not be found by simple heating, as sulphuric acid would

also be driven off,) I proceeded as follows. The hygroscopic water was first determined by heating the substance at 100°C., until the weight became constant, then by strong ignition in a platinum crucible over a gas-blast ("gas-gebläse"), all the chemically combined water and a great part of the sulphuric acid were driven off, and the loss of weight was noted after the operation. The residue was treated with hydrochloric acid, in one case, in the other it was melted with carbonate of soda, and the remaining sulphuric acid was precipitated from the solution with chlorid of barium, and determined in the usual manner. In another portion, the sulphuric acid, the whole amount was found. Knowing now the amount of water and sulphuric acid together, and of the latter alone, the water is determined by the difference. The results of the analyses are as follows:

This result agrees pretty well with the two analyses of "Gelbeisenerz" (from Bohemia and Norway) by Rammelsberg and Scheerer, given in Rammelsberg's Mineralchemie. I annex them for comparison.

The formula of the mineral therefore would be this, (+4Fe) +9Aq.; the only peculiarity being that while the above have each but one of the alkalies, they are both present in the Moronolite.

As the amount of alkali found was in all cases too small, I have taken the largest one here, instead of the average, as most correct.

ART. XXIX.-Note on the Mechanical Equivalent of Light; by MOSES G. FARMER, Electrical Engineer.

IN the October number of the L., E. and D. Philosophical Magazine is copied, from Poggendorff's Annalen, an article by Prof. J. Thomsen, of Copenhagen, on the mechanical equivalent of light.

His results show that about 13.1 foot-lbs. per minute represent the mechanical equivalent of a spermaceti candle, burning at the rate of 126 grs. per hour.

On the evening of the 4th of July, 1863, there was exhibited. by Mr. E. S. Ritchie, from the cupola of the State House in Boston, an electrical light, developed by the action of 250 Bunsen cells, arranged in five rows of 50 cells.

The intensity of this light was estimated by Prof. Wm. B. Rogers, by direct measurement, as equal to that of from 10,000 to 13,000 standard candles.

If we consider the electro-motive force of a Bunsen cell as equal to the evolution of one cubic centimeter of mixed oxygen and hydrogen gases per minute in a circuit of which the total resistance is equal to that of 4400 ft. of a round wire th of an inch in diameter, made from electrotype copper; and if we assume also the internal resistance of such a cell to be equal to 15 ft. of such wire, (these are about the average measurements), then the maximum available electrical energy, which these 250 cells would evolve, would be

Since about 614 of these units of electrical energy are the

80666666

equivalent of one unit of mechanical energy, we find 614 =131000, foot-lbs. as the mechanical energy equivalent to the light developed.

Dividing this by the estimated amount of light we get

=13.1, or

131000
13000

131000

10000

101 foot-lbs. per minute as the mechanical

equivalent of a candle light, a remarkably close agreement with the results of Prof. Thomsen.

Salem, Mass., Dec. 15, 1865.

ART. XXX.-On Scheeletine at the Southampton Lead Mine, Mas sachusetts, and Uwarowite at Wood's Chrome Mine, Texas, Pennsylvania; by CHARLES UPHAM SHEPARD.

1. Scheeletine.-This mineral was handed me for determination early in November by Mr. Clark of Northampton, who has watched with much diligence the materials thrown out during the recent working of the old Southampton lead mine. He found the few unknown crystals, of which he presented me four, occupying together a cavity in a cellular quartz gangue that appeared to have once contained galena. They prove to be Scheeletine. They are more or less coated by yellow crystals of carinthite, in small, low, double eight-sided pyramids; and one of them is also partially incrusted by a red-brown, somewhat botryoidal mineral which affords the blowpipe reaction of vanadinite, though the quantity employed in the trial did not permit a complete verification of this inference.

The scheeletine crystals are nearly half an inch long by ths of an inch in diameter, having the form of right square prisms, imperfectly terminated by acute four-sided pyramids, whose sides have an intermediary inclination betwixt the lateral edges and planes, and are therefore hemihedral. The lateral faces are not altogether plane, but present a dissected or unfinished appearance, a quality also perceptible in the terminations. The color is pale wax-yellow, passing into gray. The inner portions are grayish-black with a shade of blue, and have a submetallic luster. Otherwise the luster is adamantine.

Before the blowpipe, it decrepitates slightly. It melts easily, yielding vapors of lead, and leaves a dark gray globule. With borax on charcoal, it affords globules of lead, is yellow while hot, but becomes gray and opaque on cooling. With salt of phosphorus the color is yellow while hot; but it becomes colorless on cooling, unless the mineral is in excess, when it is greenishyellow while warm, and opaque and grayish after it is cold.

With nitric acid it is partly dissolved, leaving a yellow resi due. Ammonia throws down protoxyd of lead from the solution. The yellow residue on being fused with four times its weight of carbonate of soda containing a little nitrate of potassa, and treated with hot water, gave a colorless solution, which, after being acidulated with hydrochloric acid and the addition of metallic zinc, gave in a short time a rich blue color, from the precipitation of the oxyd of wolframium.

It is quite possible that this mineral may have been noticed before at the mine and been mistaken for cerasite or matlockite, one or the other of which, under the old name of the muriate of lead, has been supposed to exist at this locality.