preparing Aluminium. 235 



drochloi'ic acid (in platina vessels) ; tlie solution evaporated to 

 dryness with sulphuric acid and heated until the excess of acid 

 was dissipated, gave a residue which dissolved completely in 

 water with the aid of a little hydrochloric acid. Fi'om the solu- 

 tion ammonia precipitated a considerable quantity of alumina. 

 The solution filtered from the precipitate furnishedj on evapora- 

 tion, a residue of sulphate of soda free from potash. Moreover, 

 the powder gave the well-known reactions of fluorine in a marked 

 degree. 



This powder is ki-yolite of great purity ; therefore, the coarse 

 powder I first obtained was not the form in which it is originally 

 introduced. It is now to be obtained in Berlin in great masses ; 

 for the preparation of aluminium, however, it must be I'educed 

 to a very fine powder. 



In my experiments on the pi'eparation of this metal, which 

 were performed in company with M. Weber and with his most 

 zealous assistance, I made use of small iron crucibles of 1| inch 

 in height, and If inch upper diameter, which I had cast here. 

 In these I placed the finely-powdered kryolite between thin layers 

 of sodium, pressed it down tight, covered it with a good layer 

 of chloride of potassium, and closed the crucible with a well- 

 fitting porcelain cover. 



I found chloride of potassium the most advantageous flux to 

 employ ; it has the lightest specific gravity of any which could 

 be used, an important point when the slight density of alumi- 

 nium is taken into consideration ; it also increases the fusibility 

 of the fluoride of sodium. I usually employed equal weights of 

 kryolite and chloride of potassium, and for five parts of kryolite 

 I employed two parts of sodium ; the most fitting quantity for 

 the crucible was found to be 10 grms. of powdered kryolite. 

 The whole was raised to a strong red heat, by means of a blow- 

 pipe supplied with a mixture of atmospheric air and coal-gas, 

 through tubes, on the principle of Daniel's tube for the oxy- 

 hydrogen blowpipe. 



It was found most advantageous to maintain the heat for 

 about half an hour and not longer, the crucible being kept closely 

 covered the whole time ; the contents are then found to be well 

 fused. When quite cold, the melted mass is removed from the 

 crucible by means of a spatula ; this is facilitated by striking the 

 outside with a hammer. The crucible may be employed several 

 times ; at last it is broken by the blows from the hammer. 



The melted mass is treated with water, when at times only, a 

 very minute evolution of hydrogen gas is observed, which has 

 the same unpleasant odour as the gas evolved during the solution 

 of cast iron in muriatic acid. The carbon contained in this gas 

 is derived from the very slight trace of naphtha adhering to the 



112 



