INDUSTRIAL PROGRESS DURING THE YEAR 1875. cclxxxiii 



per cent.) as to entail large losses therefrom by the works, 

 while the quantities of the same are so great as to render it 

 difficult to find room for them. Dr. Hofmann has devised 

 the following process for utilizing them on a large scale : 

 The residues undergo a systematic washing, the temperature 

 of the water being about 40 C. (104 Fahr.). To the wash- 

 ings thus obtained salt is added in the proportion of one 

 equivalent for each equivalent of sulphuric acid present in 

 the liquid. The result is sulphate of soda, which is separated 

 by cooling and crystallization. This product has numerous 

 industrial applications, especially in the glass trade and in 

 the soda manufacture, and it is obtained in the present case 

 in quantity sufficient to cover the cost of all the operations. 

 The mother-liquors remaining after the sulphate of soda has 

 been separated contain zinc chloride, salt, sulphates of iron 

 and of zinc, and a further quantity of sulphate of soda. By 

 concentration to 54 B., the various salts are deposited with 

 the exception of the zinc chloride, which may then be sep- 

 arated. It has several well-known industrial applications, 

 and commands a good price. Or it may be worked for 

 metallic zinc, by being first treated with lime to convert it 

 into zinc oxide. 



The residue containing the iron originally present in the 

 pyrites, still impurified with some sulphur, is dried for some 

 days in the open air, when the bulk thereof crumbles to 

 powder, though there remain also compact fragments. 

 With regard to these masses, Dr. Hofmann has observed 

 that the pulverulent portions are almost free from sulphur, 

 which is almost completely contained in the more compact 

 fragments. A simple process of sifting suffices to separate 

 the portion free from sulphur, which is then ready for metal- 

 lurgical treatment as an iron ore. 



Professor Henry Wurtz has succeeded in devising a very 

 practical gravimetric method of gas analysis as a substitute 

 for the volumetric methods generally employed. The meth- 

 od which he recommends and which he has developed 

 with special reference to the investigation of illuminating 

 gases is founded on the general principle of submitting a 

 slow current of the gas to be investigated to the action of a 

 series of agents, so selected and combined as to absorb and 

 separate in succession, each by itself, the different proximate 



