Intelligence and Miscellaneous Articles. 473 



ON THE DECOMPOSITION OF SILICEOUS MINERALS BY MEANS 

 OF HYDROFLUORIC ACID. 



The reason this method of decomposing siliceous substances, 

 first pointed out by Berzelius, is so seldom adopted, no doubt arises 

 from the necessity of preparing pure hydrofluoric acid in platina 

 retorts, with which few chemists are provided. In order to over- 

 come this difficulty, Mr. C. Brunner has proposed to place the si- 

 liceous substance to be acted upon, in an atmosphere of hydro- 

 fluoric acid, which for this purpose he 



prepares, in a leaden vessel of this form : ^ 



the diameter is about 6 inches, and the C^III^^^^^^^^^'='^^^:=========^ 



other dimensions in proportion. In the [^-^--^^^-— --J 



middle of this vessel, supported by leaden 

 feet, a very flat platina dish is placed, in 



which is spread the siliceous substance reduced to the finest 

 powder and moistened with a little water. The bottom of the 

 leaden vessel is covered to the depth of ^ to ^ of an inch with a 

 mixture made to the consistence of a paste, of fluate of lime, and 

 sulphuric acid. A small flat cover with a wooden handle closes the 

 vessel. So provided it is submitted to the gentle heat either of a 

 sand-bath or small lamp. By means of the hydrofluoric acid gas 

 thus given out a quantity from 20 to 30 grains of siliceous mineral 

 is completely decomposed in the space of one or two hours. During 

 the progress the powder must be twice moistened with a few drops 

 of water. If the powder is well spread out at first, it is seldom 

 necessary to stir it. When this operation is finished a quantity of 

 concentrated sulphuric acid is added, drop by drop, to the powder as 

 long as any hydrofluo-silicic acid is given ofi^, at the same time it is 

 to be warmed by a spirit-lamp, and finally the excess of sulphuric 

 acid is driven off by a continued heat and evaporation to dryness. 

 The dry residue after being moistened with muriatic acid is boiled 

 in water, and further examined in the usual way. 



This method is particularly applicable to the examination of such 

 minerals as contain alkalis. — Foggendorff's Annals, No. v. 1838, 

 p. 134. 



ON THE SEPARATION OF COMPOUNDS OF OXIDES OF ANTIMONY 



AND LEAD. 



During some experiments on the decomposition and preparation 

 of a colour known in commerce by the name of Naples yellow, 

 Mr. C. Brunner found the greatest difficulty in separating this com- 

 pound. Upon most of the samples, acids had very little or no ac- 

 tion, nor did heating with alkalis effect his puqjose. He then 

 thought of converting them into sulphurets in the following man- 

 ner, which completely succeeded. About 30 grains were carefully 

 mixed with 75 grains of sulphur and 150 grains of recently heated 

 carbonate of potash, and the whole melted in a glass retort. As 

 soon as it was uniformly liquid and the dark brown mass had cooled 

 the retort was filled with water. The sulphuretted solution con- 

 tained all the antimony and the undissolved residue contained all the 



