lime, and magistral, this last, which is an acid sulphate of iron and copper, decomposes the miriate of soda; that it is formed of sulphate of soda, and muriate of silver, and that the muriate of silver is decomposed by the mercury, which unites to the disoxidated silver. It is admitted that the lime or the potash, are added to prevent the superabundant sulphuric acid from acting on the mercury. According to this explanation, the silver which is found in its mineral in the metallic state, though united with sulphur, antimony, iron*, copper, zinc†, arsenic, and lead§, passes into the state of muriate before combining with the mercury. M. Garces a Mexican author, whom we have frequently had occasion to quote, thinks on the other hand, that no muriate of silver is formed in the process of amalgamation. He supposes that muriatic acid only combines with metals which are found united with silver: that water carries off the soluble muriates of iron and copper, and that silver freed from these metallick substances, combines freely with the * In prismatic black silver. Klaproth's Beiträge, T. i. p. 166. Bergbaukunde B. i. p. 239. † In fahlore, weissgültigerz and graugültigerz, Klaproth, T. iv. p. 61. In fahlore or argentiferous grey copper. Teorica del Beneficio, p.112-116. mercury. But this explanation, apparently very simple, is contrary to the laws of affinity. If muriatic acid disengaged by the action of sulphates on the muriate of soda, were to act on any silver mineral whatever, for example, on the ore of prismatic black silver, which contains silver, iron, antimony, sulphur, copper, and arsenic, muriate of silver would necessarily be formed whenever the acid should have exhausted the other metals. The theory of M. Garces is equally inapplicable to the amalgamation of sulphuretted silver minerals, which are abundantly spread throughout the most part of the veins of Mexico. Without entering in this work into any profound discussion of the phenomena, presented by the contact of so many heterogeneous substances; and without resolving the important question, whether cold amalgamation can be carried on without salt and without magistral, I shall confine myself to the mention of several experiments. made by M. Gay Lussac, and myself, which may tend to throw some light on Mexican amalgamation. It is not true that the mixture of sulphur, entirely prevents the silver from uniting with the mercury, and that a sulphur of silver only gives cold amalgam, in adding muriate of soda and sulfate of iron: we observed on the conthat on triturating mercury and artificial trary, sulphur of silver, the mercury is quickly extinguished, and that a small quantity of silver is obtained by the distillation of the amalgam. We mixed mercury with ore of vitreous silver reduced to powder; and after a contact of 48 hours, there was formed a small quantity of silver amalgam. In this experiment and in the following, we acted on two or three grammes* of mineral, the temperature of the air being from ten to twelve centigrade degrees†, and the mixtures having been slightly moistened. On imitating the amalgamation de patio used in Mexico, and mixing in a cold state sulphur of natural silver, sulphate of iron, muriate of soda and lime, we did not find a vestige of muriate of silver, although the mixture remained in contact for a week; but we obtained it when the mass was exposed for some hours to an artificial temperature of from 30° to 34° centigrade. In the warm regions of New Spain, the tortas exposed to the sun become the most heated, and it is observed that the amalgamation takes place a great deal slower on the table lands, where the thermometer descends to the freezing point, than in the deep vallies, and in the plains in the vicinity of the coast. It is probable that the muriate of silver * 30 or 45 English grains. Trans. which is promptly formed at a temperature of 34°, would form in a long space of time at a much lower temperature. By mixing muriate of soda, sulphate of iron, and mercury in a cold state we obtain muriate of mercury; and this muriate is also obtained when we triturate mercury with muriate of artificial silver. We may easily believe that in the process of amalgamation on a great scale, a part of the mercury is converted into muriate by two distinct ways, viz. by the decomposition of the muriate of silver, and by the immediate action of magistral and salt employed in too great abundance. The lime which remedies the latter mode of action does not carry off in a cold state the sulphur from the silver; for on mixing sulphur of native silver with lime, sulphur of lime is not formed, though the mixture has been triturated for several days. The lime opposes in a very remarkable manner, the combination of silver with mercury. We observe that the latter is extinguished with difficulty, when we triturate a mixture of lime, sulphur of silver and mercury. In the same manner on forming a paste of silver mineral, salt, magistral, and mercury, and triturating the schlich till the mercury becomes invisible, we see this last metal separate from the metallick flour, and unite in considerable masses whenever lime is added. Globules of VOL. III. T mercury, which gradually increase in size, appear wherever the molecules of lime have touched the mixture; and it is from this particular action of the lime, that the azogueros assert it cools the mercury, or prevents the paste from working. The muriatic acid, disengaged from the muriate of soda by the sulphate of iron, attacks the silver, although the latter is found in its mineral in the metallic state. On treating vitreous silver with muriatic acid, we obtain muriate of silver in abundance; and on pouring the same acid on sulphur of natural silver it disengages itself from the sulphuretted hydrogen. M. Proust observed that the piastres which fell to the bottom of the sea, at the time of the memorable shipwreck of the San Pedro Alcantara, were covered in a short space of time with a crust of muriate of silver of half a millimetre✶ in thickness; and I made the same observation during my stay in Peru at the time of the shipwreck of the frigate Santa Leocadia on the South Sea coast near Cape Saint Helen. M. Pallas affirms that on the banks of the Jaik in Siberia, old Tartar coins have been found converted into muriate of silver by the contact of an earth which is impregnated with muriate of soda. All these * .0196 of an inch, Trans. |