242 ALKALIES. 



Indeed it was not known in purity until 1786, when Berthollet gave 

 the process by alcohol. 



In the ruins of Pompeii, which was overwhelmed by an eruption 

 of Vesuvius, A. D. 79, " a complete soap boiler's shop was discov- 

 ered, with soap in it, which had evidently been made by the combi- 

 nation of oil and alkali," and it was perfect, although it had been 

 made more than seventeen centuries.* 



9. TESTS FOR POTASH. j- 



1 . With an excess of tartaric acid, it forms a precipitate, which, 

 when stirred with a glass rod, forms peculiar white streaks. 



2. Muriate of platinum gives a yellow precipitate, a triple salt of 

 platinum and potash, forming, by gentle evaporation to dryness, and 

 the addition of cold water, " small shining crystals." 



3. Potash is precipitated by nothing. Turner. 



10. PHARMACEUTICAL PREPARATION AND MEDICAL USE. 



The pharmaceutical preparation does not differ materially from that 

 which has been already described for the purification of the alkali. 



The principal use of caustic potash is as an escharotic ; the cylin- 

 drical masses found in the shops, are often impure, and partially car- 

 bonated and deliquesced, and will sometimes disappoint the practi- 

 tioner. That which is carefully prepared by the process 3. (a.) and 

 (6.) is much more powerful. Potash is mixed with lime to render it 

 milder, and less deliquescent ; this is the kali causticum cum calce, of 

 the pharmacopeias. The pure alcoholic potassa, prepared by the pro- 

 cess 3. (c.) is a very certain caustic, and if fused at ignition, in the 

 conclusion of the process, broken up immediately, and put up in close 

 vials, it discovers, even in several years, no disposition to deliques- 

 cence, and preserves its crystalline structure. J 



Caustic alkali has been used as a lithontriptic. When the concre- 

 tions consist of uric acid, or urate of ammonia, there is often a favor- 

 able effect produced, but it is difficult to persist long in the use of 

 such a remedy, either by the mouth or by injection into the bladder. 



When there is to be a long perseverance in the use of alkaline 

 remedies, they must be taken in a milder form, as will be mention- 

 ed under their carbonates. 



* Parkes' Chem. Essays. 



t The nitrate, oxalate, or oxide of nickel, fused with borax, will give a blue color 

 with nitre, feldspar, or any substance containing potash, and the presence of soda 

 does not prevent the appearance of the color ; if nickel contains cobalt, the glass 

 will have a brown color. Am. Journal, Vol. XVI, p. 387. 



$ The late celebrated Dr. Nathan Smith used to obtain this alkali from the lab- 

 oratory, in all cases when he wished an energetic and certain effect, and it never dis- 

 appointed him. I have many times gone through the whole labor of preparing it 

 and although the processes are troublesome, the result is very valuable, both to 

 chemistry and medicine. 



