SECOND AEY ALTERATION OF ORES. 551 



distance to which, at Leadville, the metals appear to have been removed 



dnring secondary aheration from the original locus of deposition. 



According to J. Roth,' of such sulphates 100 parts of water dissolve, 



respectively : 



f 'f n ' n ;i;f' ^ -'"''" \ «"lpbate of lead. 

 At 13° C, 0.003155 parts f ' 



At 120 C, 21.300 parts sulphate of iron. 



At 41° C, 41.300 parts sulphate of zinc. 



The sulphate of silver is less soluble than either that of iron or of zinc, 

 but probably more so than the sulphate of lead; and at 100° C. it is said to 

 be soluble in 88 parts of water. 



Sulphide of silver may be reduced to native silver by the action of 

 water at 100° C, during which, according to Moesta, the water itself is 

 decomposed and SO3 and HS are formed. Native silver is slowly converted 

 into chloride in waters containing alkaline chlorides.^ 



Sulphide of silver is converted directly into chloride of silver at ordi- 

 nary temperatures when exposed to the action of sulphate of sesquioxide of 

 iron, chloride of sodium, and water.^ The presence of air is not necessary 

 for this reaction, but if the sulphate of protoxide of iron is substituted for 

 the basic suljjhate, chloride of silver is not produced without the presence of 

 air. This indicates that a salt of sesquioxide of iron must be formed before 

 the sulphide of silver is decomposed. 



Moesta' s^ experiments show that this reaction may take place with a 

 solution of NaCl alone at 100° C, and even at 20° C, but that it is quick- 

 ened by the presence of chloride of magnesium, and still more by pow- 

 dered pyrite; also that the combination with iodine is more rapid than with 

 chlorine. 



Sulphate of lead is transformed at the ordinary temperature into car- 

 bonate by solutions of fixed alkaline carbonates, and also by those con- 

 taining bicarbonate of lime and atmospheric air. Carbonate of lead (cerus- 

 site) is soluble in 7,144 parts of water saturated with carbonic acid.^ In 

 conversion 100 parts by weight of sulphide of lead become 126.78 of sul- 

 phate, and this in turn 111.71 parts of carbonate of lead.^ The increase 



' Allgemeiue Geologie, p. ."iO. Berlin, 18T9. 



^Percy's Metallurgy of Silver and Gold, Part I. Loudon, 1880. 



^Chlor-, Broiu- und Jodberbindungeu des Silbersiu derNatur, i). 40. Dr. Fr. A. Moesta. Mar- 

 burg, 1870. 



< Percy's Metallurgy of Lead, p. 40. London, 18T0. 'J. Roth, op. cit., p. S43. 



