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.

[Footnote:  Paper read before the Institution of Mechanical Engineers at the Cardiff meeting.—­Engineering.]

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.[1]

[Footnote 1:  Transactions of the American Institute of Mining Engineers, vol. ii., p. 159.]

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.