ON CALCAREOUS EARTH 251 



does not, as Dr. Black supposes, contain fixed air. When 



it is reduced by means of charcoal, the fixed air is to be 



deduced from the charcoal, and not from the metallic calx. 



As long as the author considers fixed air as phlogiston and 



ether, he will easily be able to explain why dry volatile 



alkali, abstracted from a metallic calx, becomes caustic. But 



a prudent chemist will not so lightly yield his assent, much 



less will he reason so much at random ; for in this case we 



have a double attraction, the fixed air, which is united with 



the volatile salt, and constitutes with it a kind of sal 



ammoniac, since it is a species of acid the fixed air, I say, 



uniting with the metallic calx, as at other times it does with 



lime, and the matter of heat in the calx joining the alkali. 



In Experiment 31 the author distilled sal ammoniac, prepared 



with volatile spirit of urine and oil of vitriol, and he obtained 



an alkaline spirit which effervesced with acids. I have 



repeated the experiment, with this difference, that I used 



spirit of sal ammoniac and not oily spirit of urine for 



saturating the vitriolic acid. My Glauber's ammoniac 



melted during the distillation, and I obtained caustic 



volatile alkali, which neither rendered lime - water turbid 



nor effervesced with acids. The residuum in the retort was 



vitriolic acid ; some of the ammoniac was also sublimed. 



The 40th experiment, too, proves nothing. He burns terra 



foliata tar tar i, or acetated vegetable alkali, and obtains a 



salt which effervesces with acids. The injudicious and 



uninstructed may indeed be easily led into mistakes by 



such experiments as this. He should know that there are 



oily particles in vinegar, and that if they were away it 



would be no vinegar at all. These oily particles, an 



essential part in all vegetable acids, are destroyed by the 



heat ; upon which the fixed air, the other constituent part 



of this oil, and indestructible in the fire, combines with the 



