Chap, i.] Dr. Black, Mr. Cavendi/b, fcfr. 



the doctrine of the aerial fluids was but in a ftate of 

 infancy, till the decifive experiments of Dr. Black, 

 Mr. Cavendifh, and Dr. Prieftley, furnifhed us with a 

 new fyftem in this important department of natural 

 hiftory. 



The firfl of rhefe philofophers obferved, that lime 

 and magnefia, in their mild ftate, confift of an union 

 of a certain aerial fluid with the earthy bafe j that this 

 aerial matter is actually extracted by the operation of 

 burning, which reduces ordinary calcareous earth to 

 the ftate of quick-lime; and th.;t it is afterwards re* 

 abforbed by the quick-lime when expofed to the air. 

 On this principle he was able, not only to account for 

 the lofs of weight by rhe burning of lime-ftone, but 

 to eftimate to the greateft nicety the additional weight 

 which it could acquire from the atmofphere. He ex- 

 tracted the gas, to which he gave the name of fixed 

 or fixable air, alfo by another procefs, namely, by dif- 

 folving the calcareous earth in acids; he found thaj 

 the caufticity of lime depended upon its violently at- 

 tracting from, vegetable ,and animal matter a portion of 

 that air of which it hacl been deprived, and that upon, 

 this principle he was enabled to render cauflic the al- 

 kaline falts. 



To Mr. Cavendifh the fecond place in the order of 

 this hiftory belongs. He purfued th-s experiments of 

 Dr. Black, and afcertained the quantity of fixed air 

 which could be retained by the fixed and volatile al- 

 kalis. He accounted for the nature of acidulated 

 waters, by the fixable air which they contained. He 

 procured a fpecies of inflammable air from folutions 

 of iron and zinc in vitriolic acid j and he was the firft 

 who remarked, that a folution of copper in fpirit of 

 fait, inltead of yielding inflammable air, lilie that of 



iron 



