Polytechnic Association Proceedings. 837 



cotton. For this purpose the fabrics are first treated with a solu- 

 tion of caustic soda lye of from 4° to 5° Baum6 left therein from 

 ten to twelve hours, then immersed in a solution of the aluminate, 

 and finally in one of sal ammoniac. 



FLUORIDE OF CALCIUM. 



The residue obtained in the manufacture of caustic, and carbonate 

 of soda forms a valuable flux for the reduction of iron ores. It pre- 

 vents the formation of graphet, and attacks the furnaces far less than 

 limestone, the usual flux. The iron is not only purer, but of a finer 

 grain, and gives sharper castings. Fluoride of calcium has also been 

 employed in the reduction of gold and silver ores. To this end, 

 its hypothetical, is, however, altogether beyond its real practical 

 value. A slight advantage in its use, over the ordinary flux, might, 

 perhaps, under proper conditions, be obtained in the smelting of 

 very silicious ores. 



HYDRATE OF ALUMINA — OTHER AND NEW USES. 



Hydi^ate of alumina, when heated with saltpetre, decomposes the 

 same — forming thereby nitric and hyponitric acids, and aluminate 

 of soda. The mixture of the two gases may be converted into 

 commercial nitric acid by the process proposed by Kuhlmann, and 

 the remainder may either be used by itself, or transformed again 

 into soda and hydrate of alumina. 



The latter may be employed further for the disintegration of 

 heavy spar. For this purpose the spar is mixed with the hydrate 

 and carbonaceous matter, and exposed to a red heat until decom- 

 posed. By lixiviating the resulting mass with water, we get a solu- 

 tion of aluminate of baryta, from which we can, by partly neutral- 

 izing the liquid with muriatic acid, obtain chloride of barium, a 

 compound largely used for the whitening of paper collars. 



It is proposed to use the h^'^drate of alumina in the desulphuriza- 

 tion of gold and silver ores. It is a well known fact that the 

 decomposition of the sulphates in the roasting of these ores requires 

 a high temperature. The disadvantage connected therewith con- 

 sists not only in a waste of fuel, but also in the melting together 

 of the non-oxidized sulphides, which as they no longer present the 

 same large surface to the air, require, comparatively speaking, a 

 a much longer time, and, in consequence thereof, a much greater 

 quantity of fuel in order to become perfectly oxidized. An admix- 

 ture of hydrate of aluiirin:!. a.'^ detained in the above described \)yo- 

 cess, or even an addition if day soil, hoAvever, readily decomposes 



