cury. The action of this last metal is rendered more energetic by the sulphates with which the mass is heated; and it is even probable that Medina only employed simultaneously, the sulphate of iron and copper, and the muriate of soda, because he discovered in these first attempts, that salt was only favourable to the process in the ores which contained decomposed pyrites. Without having any clear idea of the action of the sulphates on the muriate of soda, he endeavoured to recompose (refaire) the ores, that is to say, to add magistral to those which the miner considers as not vitriolic.

Since the practice of amalgamation of silver ores was introduced into Europe, and since the learned of every nation met at the metallurgic congress of Schemnitz*, the confused theory of Barba, and the Mexican azogueros, has been succeeded by sounder ideas, better adapted to the present state of chemistry. It is supposed that the practice of Freiberg, where a mass of roasted ores is amalgamated in a very few hours, will be gradually introduced into the amalgamation of Mexico, where the ores are generally not roasted, and where they remain exposed in the open air to the sun and the rain for several months. It is believed that in the moistened mixture of ores of silver and mercury, salt,

* Properly Szkleno or Glashütte, near Schemnitz.

lime and magistral, this last, which is an acid sulphate of iron and copper, decomposes the muriate of soda; that sulphate of soda and muriate of silver are formed, and that the latter is decomposed by the mercury which unites with the deoxidated 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 ore in the metallick state, though united with sulphur, antimony, iron*, copper, zinct, 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 the 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.

§ In weisgültigerz.

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 ore whatever, for example, on 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 ores, 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 sulphuret of silver only gives cold amalgam, in adding muriate of soda and sulphate of iron: we oberved, on the contrary, that on triturating mercury and artificial

sulphuret 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 vitreous silver ore 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 degreest, and the mixtures having been slightly moistened.

On imitating the amalgamation de patio used in Mexico, and mixing in a cold state native sulphuret of 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

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 artificial muriate of silver. It is probable 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 the magistral and salt employed in too great abundance. The lime which remedies the latter mode of action does not without the application of heat deprive the silver of its sulphur, for on mixing native sulphuret of silver with lime, no sulphuret of lime is formed, though the mixture have 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 subdued with difficulty, when we triturate a mixture of lime, sulphuret of silver, and mercury. In the same manner on forming a paste of silver ores, salt, magistral, and mercury, and triturating the whole till the mercury becomes invisible, we see this last metal separate from the metallick powder, and unite in considerable masses whenever lime is added. Globules of mercury, which gradually