Mr. Booth of Philadelphia, who is at present engaged in my laboratory, and who rendered me much assistance in these experiments, discovered at the same time a cyanid of iridium and potassium. He obtained it according to the method given by Gmelin for the corresponding platinum salt, viz., by gentle long continued ignition of a mixture of dry protocyanide of iron and potassium (prussiate of potassa) with iridium in powder. This must be performed apart from the air, for otherwise, when heated to a certain degree, the mass undergoes combustion. The coagulated mass is powdered and dissolved in water. Upon evaporation of the almost colorless solution, a portion of undecomposed iron and potassium-cyanid crystallizes and at length the salt of iridium.

Cyanide of iridium and potassium (probably protocyanide) crystallizes in long four prisms, generally in twin-crystals similar to selenite, to judge from the angle on their terminating planes. They are perfectly colorless and clear, and have not that blue and yellow opalescence, peculiar to the corresponding salt of platinum. They are soluble in water and not in alcohol, and their solution is not precipitated by sulphuretted hydrogen. They contain no water;-decrepitate strongly on being heated and become black ;-by stronger heat they fuse and iridium separates, often covering the glass with a metallic mirror.

The excess of iridium, which had been added to the potassiumiron-cyanide, and which remained after dissolving the ignited mass in water, has taken up much iron and carbon. It has now become so combustible that when ignited in one point, it continues the ignition of itself throughout the whole mass, like a pyrophorus. The iron may afterward be easily separated by digestion with hydrochloric acid.

ART. XIV.-Caricography; by Prof. C. DEWEY.

Appendix, continued from Vol. xxvI. p. 108.
No. 132. Carex incurva, Lightf.
Wahl. No. 19.

C. juncifolia, All. et Wahl. No. 17.
Schk. Tab. Hh. fig. 95.

Spiculis androgynis distigmaticis apice staminiferis in caput ovato-globosum aggregatis; fructibus ovatis subconicis teretibus subrostratis ore integris, squama ovata acuta paulo longioribus.

Culm one to two inches high, curved, with leaves sheathing at the base and longer than the culm; spikelets several, aggregated into a dense head, staminate above; stigmas two; fruit ovate, roundish and tapering, subrostrate, entire at the orifice, a little diverging; pistillate scale ovate, acute, a little shorter than the fruit: plant light green. This is a small, beautiful species found in the northern Alps of Europe; and on the Rocky Mountains, by Dr. Richardson.

No. 133, C. supina, Willd.

Wahl. No. 106.

Schk. Tab. I. fig. 41.

Spicis distinctis, staminifera solitaria; pistilliferis subbinis tristigmaticis subrotundis subsessilibus approximatis; levibus ore bilobo, squamam ovatam subæquantibus.

Culm about six inches high, slender, leafy at the base; leaves narrow and flat; staminate spike single, slender, with oblong scales whitish on the margin; pistillate spikes one or two, nearly sessile, globose, approximate, the lower with a short lanceolate bract; stigmas three; fruit roundish, subglobose, smooth, brown, rostrate, emarginate or with a two-lobed orifice; scale ovate, acutish, very nearly as long as the fruit.

This species, found in Austria and Tyrol, &c., was found also near Bear Lake in the Northern regions, by Dr. Richardson.

No. 134. C. laxa, Wahl. No. 93.

Schk. Tab. Aaa, fig. 78.

Spicis distinctis, staminifera solitaria oblonga; fructiferis tristigmaticis oblongis exserte-pedunculatis pendulis subdistantibus; fructibus ellipticis triquetro-depressis brevi-rostratis ore integris, squamam ovato-oblongam obtusam aequantibus.

Culm 6-10 inches high, sub-prostrate and flaccid; leaves shorter than the culm, sheathing, brownish towards the base; spikes distinct, staminate single, cylindric, with oblong scales sometimes slightly macronate; stigmas three; fruitful spikes one to three, pedunculate, pendulous in fruit, with short sheaths; fruit ovate and obtuse or elliptic compressed and triquetrous, entire at the orifice; scale oblong, or ovate-oblong, obtuse, sometimes with a short point, about equalling the fruit.

This carex closely resembles C. limosa, as both Wahl. and Schk. remark, and belongs in the section with this species. It is a more delicate plant, its fruit more elliptic, and its pistillate scale is shorter. and obtuse, while the other is more lanceolate. In Europe it is found in Lapland; also at the Norway House in the northern regions of America, by Dr. Richardson.

No. 135. C. ovalis, Gooden.

C. leporina, L. and Wahl. No. 35.
Schk. Tab. B. fig. 8.

Spicis androgynis, basi staminiferis, subsenis ovalibus sessilibus subapproximatis; fructibus distigmaticis ovato-ovalibus compressis acuminatis membranaceo-marginatis ore bifidis, squamam ovato-longam equantibus.

Culm twelve or twenty inches high, scabrous above, with leaves sheathing towards the base and nearly as long as the culm; spikelets about six, ovate or oval, sessile, tawny, staminate at the base; stigmas two; fruit ovato-oval, acuminate, compressed, membranaceous at the margin, bifid at the orifice; scale ovate, oblong, acutish, about as long as the fruit, whitish on the edge; plant light green.

This is the C. leporina, L., but not his plant in Flor. Dan., which is the C. lagopina of Wahl. and C. approximata of Hoppe and has only three or four spikelets different from these. The C. ovalis, Gooden. is found in England, &c., and lately on the Rocky mountains. By the plant under this name Pursh probably meant C. scoparia.

No. 136. C. Vahlii, Schk.
C. alpina, Vahl.

Sch. Tab. Gg, fig. 94 and Tab. Ppp, fig. 154.

Spicis subternis, tristigmaticis, suprema androgyna oblonga infernè staminifera, ceteris pistilliferis ovatis vel oblongis subpedunculatis brevi bracteatis; fructibus subrotundo-ellipticis triquetris ore integris, squama ovata vel oblonga subacuta majoribus.

Culm 6-10 inches high, triquetrous, smooth, leafy towards the base; leaves flat, soft, sheathing, upper ones long as the culm; stigmas three; spikes three or four, sub-umbelform, upper one oblong, staminate below; the others pistillate, ovate or oblong, subsessile, bracts longer than the culm; fruit oval, roundish, triquetrous, orifice entire, light green; scale ovate or oblong, acute or somewhat obtuse on the same spike, shorter than the fruit, and black.

Found in Alpine meadows of Lapland; and by Dr. Richardson, on the Rocky mountains, and also at the sea-coast of the Arctic regions of America, full in fruit June, 1826.

Figures of two Carices are in this volume;

C. Baldwinia, D. Tab. T. fig. 61.

ART. XV.-Communications by Dr. JOHN LOCKE, of Cincinnati.

I. Improved modification of Dr. Locke's Galvanometer.

Cincinnati Female Academy, Feb. 14, 1884.

TO PROFESSOR SILLIMAN.

Dear Sir-In my last, I sent you some account of my galvanometer as finally made in the discoid form on a wooden ring. My communication was accompanied by a drawing of the instrument as enclosed in a cylindrical box. I now communicate to you an improvement which I have since made by adding a stationary magnet. to neutralize the effect of the earth's magnetism on the needle. This magnet I have adapted to the brass tube which rises from the center of the glass cover, and encloses the filament suspending the needle. It is two and a half inches long, OP

M

and one eighth of an inch in diameter,
having a large perforation in the middle,
in which is inserted a short piece of
brass tube having an inside diameter
adapted to the suspension tube of the in-
strument. The tube and the magnet thus
connected surmount the instrument with
an ornamental cross. T The suspension
tube. P the ivory pin for winding the
filament by which the needle is suspend- volume.

F

For the drawing of the rest of this instrument, see p. 105 of this

ed. M The neutralizing magnet. S The socket slitted and springy so as to move finger tight" on T.

Experiments 1. Having adjusted the magnet to such height as nearly to neutralize the effect of terrestrial magnetism, I brought the needle to north 45° west and raised a wine-glass of river water to the battery of the instrument, consisting of a five cent piece of silver and a corresponding disc of zinc. The needle turned with an equable velocity to the north, and finally quite to the east having described an arc of 135° in twenty one seconds.

2. Having procured a rude piece of antimony and a strip of sheet copper I connected them with the wires of the galvanometer and finally with each other, having previously warmed the copper by holding it in my hands. The needle was deflected 80°.

3. I applied the two wires to the two extremes of the piece of antimony, which was about three inches long and one a half thick, pressing one wire to it with a piece of wood and the other with my thumb and finger. The warmth of the hand, thus applied caused the needle to turn 76° when the wood and the fingers were changed to the opposite extremes, the needle reversed its motion.

Whether the above experiments indicate any superior delicacy in the instrument I am not able to say. So far as my own experience goes, it excels by far all other modifications.

II. Experiments, March 12th, 1834.

The most delicate experiments which I have made, are as follows:

1. When the needle is nearly neutralized by the fixed magnet, the application of river water to the 5 cent piece battery will turn the needle 90°; and often by impulse throw it entirely round.

2. The poles (copper wires) of the instrument being held to the extremes of a piece of antimony as large as a hen's egg, the one by a piece of wood and the other by the fingers, the needle will turn 90° in consequence of the thermo-electricity generated by the heat of the fingers.

3. Two discs of copper attached to the poles, and half an inch in diameter including a disc of antimony of the same size caused the needle to turn 90° upon the application of the end of the finger to one of the copper discs.