1 826.] as carried on in Germany. 265 



through the mass, but will remain in a great degree stagnant. If 

 the mixture is found to be too much diluted, it must be corrected 

 by adding a little ore; if it be too thick, a little water should be 

 introduced. Attention must also be paid to the velocity with 

 which the barrels are made to revolve ; as by any material devia- 

 tion from that degree, which, from experience, has been found 

 best calculated to produce the desired result, nearly the same 

 effect will follow as when the mass is improperly mixed. If the 

 barrels are made to revolve too rapidly, the particles of mercury 

 will collect round the sides. The consistency of the mixture 

 should be occasionally ascertained by stopping a barrel, opening 

 the bung-hole, and dipping a stick into it (if, on withdrawing the 

 rod, the ore drops slowly from it, it is considered in a proper 

 state) ; and before the process is completed, a sample of the ore 

 should be taken, and tried in a crucible, and the operation conti- 

 nued if found to contain any considerable portion of silver. 

 Attention should also be paid to the state of the mercury in the 

 mixture, which should be minutely disseminated throughout the 

 mass, and the globules not larger in size than the head of a pin. 



After the barrels have been a few hours in motion, it will be 

 found that the temperature of the mixture has been considerably 

 increased ; and as heat materially assists the amalgamation, this 

 mode of obtaining it by revolving barrels, without the aid of ex- 

 ternal fires, to which they were formerly obliged to have recourse, 

 is one of the greatest discoveries that were made by De Born, 

 I should have observed, that to De Born, I believe, is also due 

 the merit of organizing, the system of previous calcination of 

 the ore with salt; although the mode of operation was improved 

 by Gellert in the construction of the Freyberg works. 



On the opening of a barrel, a strong acid smell may be per- 

 ceived, and particularly towards the end of the process. This 

 arises from the chemical changes that take place ; the muriates 

 which were formed by the calcination are decomposed ; the iron 

 unites with the muriatic acid ; and the metallic silver, and a 

 portion of copper, or other metals, contained in the ore, combine 

 with the mercury. The muriate of iron, being a soluble salt, 

 becomes dissolved in the water, as do the sulphate and the other 

 salts of soda. 



It is obvious that a deficiency of iron in the barrel will prevent 

 the decomposition of the muriate of silver from taking place; 

 care should therefore be had, to keep a proper supply of iron in 

 the barrels. 



The next process that requires to be noticed, is the separation 

 of the two metals contained in the amalgam, which is effected by 

 their different degrees of fusibility. The amalgam is exposed 

 in a furnace of a peculiar description, to a certain degree of heat, 

 when the mercury is sublimated, or distilled, and the silver 

 remains. 



When the furnace is charged and arranged, the weight of amal- 



