lfi4 PuriJit-:itlon of FixeJ jitltnlir. 



VI. 



The Method of ohtaining the FixeJ Alkalis iti CryJIah of the greatejl Purity. By LoiriTZ, 



Prcffor, l^c. at Psterfiiirg *. 



I. 1 HI 



IE cauftic alkalis, as obtained by the ordinary proceflcs, are fufficiently pure for the 

 purpofes of pharmacy and the arts ; but for the experiments of philofophical chemillry the 

 greatcil purity is required in every fubftancc made ufe of. » 



2. Cauftic alkalis have hitherto been very fcldom ufed in the analyfis of mineral fubflances. 

 M. Klaproth f has fhewn their utility in analyfes, not only in e(fe£ting a more eafy fepara- 

 tion of aluminous earth, but likewife to difunite the principles of the mofl refraflory foflils. 

 This circumftancc has induced nie to give a more particular defcription of the difcovery I 

 made fome years ago of the cryftallization of the cauftic alkalis, as the principal means of 

 obtaining them in a flate of abfolute purity. I have likewife embraced this opportunity of 

 rectifying the millake of various chemills, who have imagined that cryftallization cannot 

 take place but during the moll extreme cold of winter. 



3. My firft experiments on vegetable alkali were made in the hotteft days of fummer, 

 and the mod bc.iutlful cryftjilization was formed even over the fire. 



4. The cryftallization of foda does not fucceed but in winter ; but the ordinary cold 

 of five degrees (R.) is fufficient for this cfleft. The reafon why this alkali requires fo low a 

 temperature arifes from the property its cryftaJs poflefs of being foluble at tlie flighted heat 

 in their own water of cryftallization. The fame thing is obfervable in the muriate of 

 foda or common fait cryftallized by cold %. 



5. Before the difcovery of this method, no one had fuccecded by the ordinary procefles to 

 obtain a colourlefs lixivium of cauftic alkali. Thefe folutions were always more or lefs 

 brown. By repeated cryftallizations this lixivium may be had in the moft concentrated 

 Rate, as limpid as the pureft water; which inconteftably proves that the common lixivia are 

 contaminated by heterogeneous matters, which charcoal and the ftrongeft calcination are 

 incapable of deftroying. 



6. The whole of the operation for obtaining a cauftic alkali of the greateft purity and 

 without the leaft colour, confifts in this : A cauftic lixivium of pot-afli is evaporated to a 

 thick pellicle. After the cooling, the foreign fait which has cryftallized is to be feparated, 

 and the evaporation of the lixivium continued in an iron pot, as in the preparation of the 

 lapis caufticus. During this fecond evaporation the pellicle of foreign falts, particularly 

 of carbonate of pot-afti, which continues to be formed, muft be carefully taken ofl" with 

 an iron ftimmer. When no more pellicle is formed, and the matter ceafes to boil up, 

 it is removed from the fire, and fuffered to cool, with continual agitation by an iron fpa- 

 tula. It is then to be diflblved in double the quantity of cold water, the folution filtered, 



* Von Crcll's Chcmifchc Annalen auf 1796, b. i. f. 506. 



+ Beytragc 2ur Chcmifchtn Kenninifs dcr Mineral Koerper, b. i. 



\ I.owitz obtained this fingular cryfiallizaiion of the muriate of foda by expoGng a folution of this fait to in- 

 teofc cold. The cryftals, which are hexagonal, are two inches in diameter, and one line thick. They liquefy 

 jr a few degrees below the freezing point of water, and fall into a very fine white powder at an extremely low 

 uinpcrarore. Note of Van Mons in the Annals of Chcmiftry, XXII. 17. 



5 and 



