LEAD-PIGMENTS. 107 



and arsenic, are obtained from copper and other ores. These 

 mingled ores are hardly likely to yield the several products 

 sufficiently separate and distinct. 



Rochaz has a good arrangement for making this pigment 

 direct from metallic zinc by combustion. (Lond. Journ. xxxvi. 

 1.) Fire-clay crucibles are set each in a furnace, so that the 

 fire plays around but not above it. The zinc being thrown in 

 and brought to ignition, the cover of the crucible is removed 

 and a draft of air passes over the crucible, whereby oxide of 

 zinc is produced, forming abundant white fumes, which are 

 carried into a large chamber, divided into compartments. The 

 greater part of the oxide settles in these ; and to prevent any 

 appreciable quantity from passing off, the last compartment 

 is provided with hanging bands of hemp or other fabric, which 

 may be multiplied without interfering with the draft. He 

 proposes to use the Belgian furnace for distilling metallic zinc 

 from its ores, consisting of a stack of many cylindrical retorts, 

 in order to prepare the white oxide from the ore, and varying 

 the arrangement so that the air is admitted to the distilling 

 metal, whereby it is converted into oxide, and condenses in 

 chambers. Several forms of blast-furnace have been proposed, 

 but none have been proved sufficiently to speak of their merits. 



The native oxide of zinc of New Jersey has been recently 

 employed both for making the metal and zinc-white. The 

 former is less likely to be economically produced than the 

 latter ; and it is stated that the process for the latter is emi- 

 nently successful, as it requires but 2 pts. coal to obtain 1 pt. 

 of the pigment. Judging from the experience in Europe, we 

 must believe this to be a great miscalculation, for it requires 

 some 11 tons fuel to make 1 ton zinc in Belgium and Silesia, 

 and in making the oxide of zinc, the formation of metal must 

 precede it. 



A case of the peculiar effect of zinc in producing a colic 

 among operatives engaged in making it, is reported in the 

 Comptes Rendus, and although it appears to be less delete- 

 rious than white-lead, yet it shows that its effects on workmen 

 must also be guarded against. 



