MATTES. 



723 



Analysis XXXIX. Iron sow. 



ain order to obtain a fair average assay of silver .and gold ttio assay was toade on 200 

 grams, which explains why gold is given to the TjinrnrTi of an ounce to the ton. 



Analysis XXXIX sliows tbat tbe sow.s are an alloy of iron and lead combined 

 with a quantity of arsenic sufficient to class tbem with speiss. Like the latter, sows 

 contain nickel, niolybdennm, and sulphur. Their graphite is liberated when their iron 

 enters into combination with larger quantities of sulphur and arsenic, and is blown 

 away with the lead dust where it has been found. Like supersaturated speiss, sows 

 are very rich iu silver. The fact that they contain traces of cobalt, which cannot be 

 detected in speiss, shows that this metal is forcibly taken away by virtue of a reaction 

 which is not yet understood, although one is inclined to presume that sulphide of 

 cobalt is formed, and that it combines more readily with sulphide of lead than with 

 arsenide of iron. 



MATTES. 



The examination of the mattes of Leadville proved so surprising to the writer 

 that he accumulated all possible proofs in order to have no doubts as to their nature. 

 It will be seen that thej* are formed of sulphides of irou and lead and magnetic oxide 

 of iron. It was in order to demonstrate the piesence of this oxide that experiments 

 and reactions were varied in every pos.sible way, which were discarded afterwards, 

 and became useless when the magnetic oxide of iron was successfully isolated iu the 

 pure crystalliue state. Thus mattes are formed of sulphides aud oxides, and, like 

 most furnace products, they are crystaHographic comhiiiafious of chemical compounds. 



A careful examination was made of the two typical kinds of mattes of Leadville. 

 The so-called iron matte, with a fine crystalline structure and a brown luster, was col- 

 lected at jMe«.sr.s. Cumming & Finn's smelter (Analysis XL). The so called lead 

 matte, blackish gray, with a decided crystalline structure, was found at the Elgin 

 smelter (Analysis XLI). Both specimens were slightly swollen aud split by a begin- 

 ning of oxidation. Both yield strongly magnetic particles to the magnet, which were 

 at fii>t mistaken for magnetic sulphides. By rubbing the magnetic i)orticn on filter 

 paper, isolating with the magnet, repeating the operation several times, and finally 

 treating it with nitric acid, in order to destroy some sulphides which adhere to it, 

 the pure magnetic oxide is obtained. Whether the adhering sulphides are magnetic 

 or not could not be decided. The pure magnetic oxide was not analyzed, but there is 

 but little doubt that its formula is the same as that of the oxide isolated from slags, 

 namely, Fe^Og. 



