238 Prof. Rose on a new and advantageous Method of 



I repeatedly employed chloride of sodium (common salt de- 

 crepitated) as a flux in the absence of chloride of potassium with- 

 out remarking any important diflFerence in the amount of metal 

 produced, although a higher temperature is required in that case. 



The operation may also be conducted in unglazed crucibles of 

 difficultly fusible stone-ware of the above dimensions, although 

 they do not resist the action of fluoride of sodium at very 

 high temperatures so well, but fuse in one or more places. The 

 iron crucibles fuse, however, when exposed to a very high tem- 

 perature in a charcoal fire. 



The produce in metal was found to vary much, even when 

 operating exactly in the manner recommended, and with the 

 same quantities of the materials. I never succeeded in reducing 

 the whole amount of metal contained in the kryolite ; it con- 

 tains only 13 per cent, of aluminium ; by operating on 10 grms. 

 of the mineral, the quantity I always employed in the small 

 iron crucibles, the most successful result was 0-8 grra. But 0*6 

 grm., or even 0*4 grm. may be considered favourable. Many 

 times I obtained only 0-3 grm., or even less. 



These very different results depend on various causes, more 

 particularlj', however, upon the degree of heat obtained. The 

 greater the heat, the greater the amount of larger globules, and 

 the less amount of minutely divided aluminium to oxidise during 

 the cooling of the cracible. I succeeded once or twice in re- 

 ducing nearly the whole of the metal obtained to one single | 

 button, weighing 0*5 grm. at a very high temperature in a stone- I 

 ware crucible. I 



I could not always attain the same heat with the blowpipe, n 



as it depended in some degree upon the pressure in the gaso- 

 meter at the gas-works, which varies at different periods of the ^ 

 day. The following experiment will show how great the loss of 9 

 aluminium may be owing to the oxidation of the metal dux'ing 

 the slow cooling of the crucible and contents. 



In a large iron crucible were placed 35 grms. of kryolite in 

 alternate layers with 14 grms. of sodium, and the whole covered 

 with a thick stratum of chloride of potassium. The crucible 

 closed with a porcelain cover, was placed in a larger earthen one 

 also covered, and the whole exposed to a good heat in a draft 

 furnace for one hour, and cooled as slowly as possible. The 

 produce in this case was remarkably small, for 0"135 grm. of 

 aluminium was all that could be obtained in globules. 



The difference in the amount reduced depends also in some 

 degree on the more or less successful stratification of the sodium 

 with the powdered kryolite, as much of the latter sometimes 

 escapes decomposition. The greater the amount of sodium 

 employed, the less hkely is this to be the case ; however, 



