the water project, according to requirement, more and more above the sawdust. The ice cylinder shows on its basis a very regular hemispherical cavity, which progresses unaltered until its edges touch the mercury by b, and the last portions of water have been frozen from above downward. After the formation of ice is at an end, the instrument is still exposed some time to a temperature below 0° C. in order to freeze the last traces of water which exist by b between the mercury and the glass walls. The ice cylinder thus formed is perfectly free from air bubbles, and equals in clearness and transparency the finest crystal glass. The piece of apparatus designated in the figure with the letter B is now combined, by means of the cork e forcibly pressed in, with the open limb of the apparatus A in such a manner that not a trace of air is included between the cork and mercury, whereby the displaced mercury flows through the capillary tube f into the glass vessel, which is filled with mercury to g. The capillary tube is cemented with the finest sealing-wax into the smooth and perfectly poreless cork. To cement the cork likewise on the wider tube in which it sits, would be wholly superfluous, as a displacement is as little to be feared as an elastic effect afterward, as I have convinced myself by direct experiment. The instrument thus arranged is placed in a room having the greatest possible constancy of temperature, and is surrounded on all sides with a thick envelope of snow which has, at a temperature above 0° C., become completely coherent without at the same time becoming saturated with water. When, after 6 to 12 hours, the entire instrument has attained 0° C., the mercury vessel is removed from the cork h, weighed with the mercury it contains, and, after any mercury which may still adhere to the capillary tube, has been carefully removed, returned to its place. The apparatus is then removed from its envelope of snow, the ice it contains is melted by radiation from a non-luminous gas flame brought in its neighborhood, and it is permitted to attain as before in an envelope of snow, the temperature of 0° C. The mercury vessel is now removed and reweighed. The loss in weight, compared with the first weighing, is the weight of the mercury, whose volume calculated for 0° C. expresses the diminution in volume which the ice cylinder at 0° C. has suffered in melting to water at the same temperature.

Let G be the weight of the water frozen,

го

G, the weight of mercury which entered the instrument
during the melting of the ice,

So the specific gravity of water at 0° C.,
S the specific gravity of mercury at 0° C.,
S the specific gravity of ice at 0° C.,

On account of the great accuracy which the method just described permits, it appeared to me superfluous to make more than three experiments. In the first of these the water froze between -3° C. and -5° C., in the second between -1° C. and -3° C., in the third between 0° C. and -2° C. The following weights, reduced to vacuo, were obtained:

then the resulting specific gravity of ice S, will be:

We have therefore for the terms occurring in equation (2),

The weight of melted ice e which corresponds to T corrected divisions on the scale is therefore:

Let the latent heat of melting, for water, be l, then will one scale division correspond to pl of the previously defined units of heat. For the amount of heat w, expressed in units of heat, which is indicated by T scale divisions, we have therefore,

w = plT

or, if the value 80.025, hereafter to be determined, be substi tuted for 1,

As the ice cylinder which surrounds the vessel a weighs forty to fifty grams, and it is necessary, on the average, to melt by each experiment only about 0:35 grams of ice, which corresponds to rather more than four hundred scale divisions, it is possible to make with the same ice cylinder as many as 100 different calorimetric determinations and to use the apparatus, arranged once for all, for weeks at a time, when care has been taken that the snow which surrounds the instrument be morning and evening renewed by refilling.

The ice cylinder may be easily produced by a contrivance which is rendered intelligible by fig. 2: A is a sheet tin vessel containing alcohol, B an empty one, both of which are cooled to about -20° C. in a freezing mixture of salt and snow. C represents the inner vessel a fig. 1, around which the ice cylinder is to be produced. If suction be applied to the tube a, the cooled alcohol of the vessel A will be carried through the vessel C into the vessel B; if suction be then applied in the opposite direction by means of the tube b, the alcohol will return through the vessel C into the vessel A. By alternate suction at a and b, the vessel C may be kept to the height a as long as desired at a temperature of -10° C. to -15° C., by means of continually renewed cooled alcohol, and the required ice envelope will be produced in the water mass surrounding the vessel C which is denoted in fig. 1 by b. I have given this ice-producing apparatus the form, fig. 3. The two semi-cylindrical tin vessels a and b, which communicate with one another and with the tube a by means of tubes above and below, correspond to the single vessel A fig. 2, the precisely similar tin vessels opposite these, the outer one of which is denoted by e, correspond to the vessel B in fig. 2. These two vessels, each consisting of two concentric chambers, together with the tube a, possess, as may be seen, a very large cooling surface, and are sunk in one and the same freezing mixture. The arrangement of the system of tubes, fig. 3, by means of which the circulation of the cooled alcohol is effected, is rendered easy of comprehension, from the fact that the corresponding rubber tubes are designated by the same letters as in fig. 2. The alternate suction to and fro of the alcohol is regulated by the alternating cock H, which communicates with the water air-pump by means of the rubber tube w. When this cock is in the one position the rubber tube q communicates with the suction tube w, the tube p however with the atmosphere; in the other position the order is reversed, the suction tube w communicates with the rubber tube p, and 9 with the outer air. By means of this contrivance, the production of the ice cylinder becomes a very simple operation. The cooling apparatus with its attached rubber tubes is placed in the freezing mixture, p and q are connected with the alternating cock H, w with the water air-pump, the rubber stopper

with its tubes m and n is sunk by C in the inner vessel of the instrument, and finally the tubes m and n are placed on the corresponding glass tubes of the cooling apparatus. If now, after the cock of the water air-pump has been opened, the alternating cock be turned alternately back and forth, the cooled alcohol stream may be allowed to operate as long as you please in producing the ice cylinder. The formation of the latter in the apparatus, which stands quite free in the room, may be beautifully observed with the naked eye or through the telescope, and presents not uninteresting peculiarities. The temperature of the perfectly airless water in the outer vessel b, fig. 1, sinks gradually, without freezing taking place, until far below 0° C., while the vessel covers itself externally with an ice crust from the precipitated moisture of the atmosphere; even strong agitation is insufficient to put a stop to this abnormal fluidity. When the temperature has finally sunk very low, a sudden formation of ice takes place, which propagates itself in a few seconds from A to μ. The whole vessel is filled down to this limit with milky turbid leaves and needles of ice, the water mass from μ to the mercury surface is on the contrary unfrozen. Now begins, under continued cooling, the first formation of the ice. cylinder, which is allowed to increase until its walls have attained a thickness of about 6 to 10mm. That part of the very regularly formed ice crust which lies below u appears perfectly amorphous, clear and transparent as the purest crystal glass; the portion above u reaching to λ appears turbid and of a texture not dissimilar to the confused coarse-fibrous, after the instrument has stood several days ready for use at 0° C. in the snow this coarse-fibrous texture changes entirely. The ice mass between A and μ consists now of small rounded transparent grains of spherical habitus; if, after long use, the instrument be exposed to the temperature of the room, the individual spheres melt off on their surfaces, detach themselves thereby from the adjacent mass, and rise in the fluid; they then appear at times connected with one another like the cells of yeast.

[To be continued.]

ART. XXVII.-On the Porcelain rock of China; by Baron VON RICHTHOFEN.-From a letter to Prof. J. D. WHITNEY, dated Shanghai, Nov. 17, 1869.

I HAVE recently made a very pleasant trip of six weeks, going up the Yang-tse to Kinkiang, then into Poyang lake. I visited some places on its eastern affluents, among them the famous King-te-chin, where the Chinese have made nearly all their porcelain for almost three thousand years. I examined the places from which they take the material, crossed over into

An-hwei and Che-Kiang, and descended the Tsien-tang river to Hang-chan, whence I returned to Shanghai. This is probably one of the prettiest countries in China. The hills are overgrown with that prolific vegetation of Azaleas, Rhododendrons, Weigelia and numberless other kinds of low shrubbery which, on account of their beautiful flowers, justify the appellation of the "Flowery Kingdom," at least for this portion of China.

Its geology is rather monotonous, but by no means devoid of interest. Hardly anything is to be seen of the limestones otherwise so prevalent in China. On the eastern slope, sandstones occupy the field almost exclusively. They are folded up to high mountain ranges. Next to them in bulk are porphyries (both quartzose porphyry and porphyrite). The greater portion of the sandstones was certainly, the rest probably, deposited in and after the period of the eruption of the porphyric rocks. I cannot undertake to make an estimate of their stupendous aggregate thickness. Yet, they are surpassed in this respect by a formation on which they are superposed in the neighborhood of the watershed. It consists of clayslates, with sandstones occasionally imbedded; the whole formation stands on edge and preserves a W.S. W. to E.N.E. strike with remarkable regularity, the strata dipping at angles of 70 to 80 degrees alternately N.N.W and S.S.E. During a journey of about one hundred and thirty miles, going from S.S. W. to N.N.E., or at an angle of about 45 degrees with the strike of the rocks, I traversed no other formation but those same slates, standing on edge. This was on the western slope of the range. I have to record the unexpected fact, that the material from which the procelain of King-te-chin is made is taken from certain strata intercalated between these slates, and occurring at several places, separated from each other laterally, that is, at angles with the strike of the rocks. It is a rock of the hardness of feldspar (inferior kinds are not so hard), and of a green color, which gives it in some measure the appearance of jade, to which the Chinese, too, compare it. This rock is reduced, by stamping, to a white powder, of which the finest portion is ingeniously and repeatedly separated. This is then moulded into small bricks. The Chinese distinguish chiefly two kinds of this material. Either of them is sold in King-te-chin in the shape of bricks, and as either is a white earth, they offer no visible differences. They are made at different places, in the manner described, by pounding hard rock, but the aspect of the rock is nearly alike in both For one of these two kinds of material, the place Kaoling ("high ridge,") was in ancient times in high repute; and, though it has lost its prestige since centuries, the Chinese still designate by the name "Kao-ling," the kind of earth which was formerly derived from there, but is now prepared in other places. The application of the name, by Berzelius, to por

cases.