temperature of the solar surface does not reach 3,000° C.

J. ERICSSON.

CHEMICAL NATURE OF STARCH GRAINS.

Dr. Brukner has contributed to the Proceedings of the Vienna Academy of Sciences a paper on the "Chemical Nature of the Different Varieties of Starch," especially in reference to the question whether the granulose of Nageli, the soluble starch of Jessen, the amylodextrin of W. Nageli, and the amidulin of Nasse are the same or different substances. A single experiment will serve to show that under certain conditions a soluble substance maybe obtained from starch grains.

If dried starch grains are rubbed between two glass plates, the grains will be seen under the microscope to be fissured, and if then wetted and filtered, the filtrate will be a perfectly clear liquid showing a strong starch reaction with iodine. Since no solution is obtained from uninjured grains, even after soaking for weeks in water, Brukner concludes that the outer layers of the starch grains form a membrane protecting the interior soluble layers from the action of the water.

The soluble filtrate from starch paste also contains a substance identical with granulose. Between the two kinds of starch, the granular and that contained in paste, there is no chemical but only a physical difference, depending on the condition of aggregation of their micellæ.

W. Nageli maintains that granulose, or soluble starch, differs from amylodextrin in the former being precipitated by tannic acid and acetate of lead, while the latter is not. Brukner fails to confirm this difference, obtaining a voluminous precipitate with tannic acid and acetate of lead in the case of both substances. Another difference maintained by Nageli, that freshly precipitated starch is insoluble, amylodextrin soluble in water, is also contested; the author finding that granulose is soluble to a considerable extent in water, not only immediately after precipitation, but when it has remained for twenty-four hours under absolute alcohol. Other differences pointed out by W. Nageli, Brukner also maintains to be non-existent, and he regards amidulin and amylodextrin as identical. Brucke gave the name erythrogranulose to a substance nearly related to granulose, but with a stronger affinity for iodine, and receiving from it not a blue but a red color. Brukner regards the red color as resulting from a mixture of erythrodextrin, and the greater solubility of this substance in water.

If a mixture of filtered potato starch paste and erythrodextrin is dried in a watch glass covered with a thin pellicle of collodion, and a drop of iodine solution placed on the latter, it penetrates very slowly through the pellicle, the dextrin becoming first tinctured with red, and the granulose afterward with blue. If, on the other hand, no erythrodextrin is used, the diffusion of the iodine causes at once simply a blue coloring.

With regard to the iodine reaction of starch, Brukner contests Sachsse's view as to the loss of color of iodide of starch at a high temperature. He shows that the iodide may resist heat, and that the loss of color depends on the greater attraction of water for iodine as compared with starch, and the greater solubility of iodine in water at high temperatures.

The different kinds of starch do not take the same tint with the same quantity of (solid) iodine. That from the potato arum gives a blue, and that from wheat and rice a violet tint; while the filtrate from starch paste, from whatever source, always gives a blue color.

THE AMALGAMATION OF SILVER ORES.

DESCRIPTION OF THE FRANCKE "TINA" OR VAT PROCESS FOR THE AMALGAMATION OF SILVER ORES.^[1]

By Mr. EDGAR P. RATHBONE, of London.

In the year 1882, while on a visit to some of the great silver mines in Bolivia, an opportunity was afforded the writer of inspecting a new and successful process for the treatment of silver ores, the invention of Herr Francke, a German gentleman long resident in Bolivia, whose acquaintance the writer had also the pleasure of making. After many years of tedious working devoted to experiments bearing on the metallurgical treatment of rich but refractory silver ores, the inventor has successfully introduced the process of which it is proposed in this paper to give a description, and which has, by its satisfactory working, entirely eclipsed all other plans hitherto tried in Bolivia, Peru, and Chili. The Francke "tina" process is based on the same metallurgical principles as the system described by Alonzo Barba in 1640, and also on those introduced into the States in more recent times under the name of the Washoe process.^[2]

It was only after a long and careful study of these two processes, and by making close observations and experiments on other plans, which had up to that time been tried with more or less success in Bolivia, Peru, and Chili—such as the Mexican amalgamation process, technically known as the "patio" process; the improved Freiberg barrel amalgamation process; as used at Copiapo; and the "Kronke" process—that Herr Francke eventually succeeded in devising his new process, and by its means treating economically the rich but refractory silver ores, such as those found at the celebrated Huanchaca and Guadalupe mines in Potosi, Bolivia. In this description of the process the writer will endeavor to enter into every possible detail having a practical bearing on the final results; and with this view he commences with the actual separation of the ores at the mines.

Ore Dressing, etc.—This consists simply in the separation of the ore by hand at the mines into different qualities, by women and boys with small hammers, the process being that known as "cobbing" in Cornwall. The object of this separation is twofold: first to separate the rich parts from the poor as they come together in the same lump of ore, otherwise rich pieces might go undetected; and, secondly, to reduce the whole body of ore coming from the mine to such convenient size as permits of its being fed directly into the stamps battery. The reason for this separation not being effected by those mechanical appliances so common in most ore dressing establishments, such as stone breakers or crushing rolls, is simply because the ores are so rich in silver, and frequently of such a brittle nature, that any undue pulverization would certainly result in a great loss of silver, as a large amount would be carried away in the form of fine dust. So much attention is indeed required in this department that it is found requisite to institute strict superintendence in the sorting or cobbing sheds, in order to prevent as far as practicable any improper diminution of the ores. According to the above method, the ores coming from the mine are classified into the four following divisions:

1. Very rich ore, averaging about six per cent. of silver, or containing say 2,000 ounces of silver to the ton (of 2,000 lb.).

2. Rich ore, averaging about one per cent. of silver, or say from 300 to 400 ounces of silver to the ton.

3. Ordinary ore, averaging about ½ per cent. of silver, or say from 150 oz. to 200 oz. of silver to the ton.

4. Gangue, or waste rock, thrown on the dump heaps.

The first of these qualities—the very rich ore—is so valuable as to render advantageous its direct export in the raw state to the coast for shipment to Europe. The cost of fuel in Bolivia forms so considerable a charge in smelting operations, that the cost of freight to Europe on very rich silver ores works out at a relatively insignificant figure, when compared with the cost of