86 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



EIVOT METHOD OF EXTRACTING GOLD AND SILVER. 



A new process of extracting gold and silver from their 

 ores, devised by Rivot for treating the California ores, has 

 been lately published, and is said to be applicable under cer- 

 tain circumstances in which the usual methods can not so 

 readily be employed. The principal stages in this method 

 of treatment are presented in the following summary : 



1. Roasting of the pyrites in heaps, or in reverberatory fur- 

 naces, in such a manner as to almost completely oxidize the 

 metallic sulphides, and to reduce the formation of sulphates 

 to a minimum. 



2. Pulverizing and mixing of the roasted pyrites with the 

 ores. 



3. Roasting of the mixed mass with superheated steam in 

 a revolving furnace, with exclusion of air. 



4. Amalgamation in vertical mills, which are capable of a 

 great out-turn, and of working wet or dry, as may be de- 

 sired, and which divide the mercury well, and effect a more 

 speedy and complete amalgamation, owing to the pressure 

 of the millstones. ' 



5. Separation of the mercury from the residues. 



6. Squeezing of the mercury through coarse linen bags or 

 wooden cylinders. 



7. Distillation of the amalgam in cast-iron tubes provided 

 with receivers cooled .by water. 



8. Smelting of the metals recovered by amalgamation in 

 black-lead crucibles, and casting in iron moulds. 21 A,Dec.^ 

 1871,1219. 



ESTIMATING SULPHUR. IN COAL. 



A method for the estimation of sulphur in coal or coke, in- 

 troduced by Dr. Crace Calvert, has reference more particular- 

 ly to the combination of sulphur with iron, as being the only 

 combination affecting the commercial value of the fuel. The 

 process consists in boiling the powdered coal in a solution 

 of carbonate of soda, which decomposes any sulphate of lime, 

 the carbonate of lime being removable by washing. In the 

 residue is contained the combination of sulphur and iron, 

 which can be estimated by any of the methods familiar to 

 chemists. 15 A, August 12,1871,209. 



