"OL. LXXII.j PHILOSOPHICAL TRANSACTIONS. 263 



solved in the same quantity of the same spirit of salt, and the air received over 

 mercury, afforded 9 1. 28 cubic inches of air ; but of these only 4.Q cubic inches 

 were inflammable air ; the remainder therefore, viz. 86.38, were marine air, 

 which weigh 56.49 gr. 



Now, as spirit of salt certainly does not dephlogisticate copper more than the 

 vitriolic acid does, it follows, that these 4.9 cubic inches of inflammable air, and 

 86.38 cubic inches of marine air, do not contain more phlogiston than would 

 be separated from the same quantity of copper by the vitriolic acid : and since 

 100 grains of copper would yield to the vitriolic acid 4.32 gr. of phlogiston, 8.5 

 gr. of copper would yield O.367 of a grain of phlogiston ; this then is the whole 

 quantity extracted by the marine acid, and contained in Q1.28 cubic inches of air, 

 and deducting from this the quantity of phlogiston contained in 4.9 cubic inches 

 of inflammable air (= 0.171 of a grain,) the remainder, viz. O.367 — 0.171 = 

 0.196, is all the phlogiston that can be found in 80.38 cubic inches of marine 

 air. Then 100 cubic inches of marine air can contain but 0.227 nearly of a grain 

 of phlogiston, 65.173 of acid. Hence we see why it acts so feebly on oils, spirit 

 of wine, &c. having a very small affinity to phlogiston ; and why it is not dis- 

 lodged from any basis by uniting with phlogiston, as the vitriolic and nitrous 

 acids are, its affinity to it being inconsiderable. 



XVI. Of the Method of rendering very sensible the weakest Natural or Artificial 

 Electricity. By Mr. Alexander Volta, Professor of Experimental Philosophy 

 in Como, &c. &c. From the Italian, p. 237. 



Whenever, in observing the atmospherical electricity, no degree of it can be 

 discovered by the ordinary methods of performing those experiments, it is diffi- 

 cult to determine whether any electricity at all does or does not exist in the at- 

 mosphere at those times ; since it may exist, and the quantity of it onlv be so 

 small as not to affect the electrometers employed. In that case therefore, if we 

 rely on the common electrometers, even the most sensible, we must conclude, 

 that neither the conductor nor the atmosphere, so high as the conductor reaches, 

 contain any electricity ; but by means of the apparatus here described, it will 

 be found, that the said conductors are never entirely void of electricity, and 

 consequently the air, which surrounds them, is also at all times electrified. This 

 method not only shows the existence of electricity, but also ascertains whether it 

 is positive or negative, and that when the atmospherical conductor itself is not 

 capable of attracting the finest thread ; and if the conductor were to show any 

 very small attraction, then, by means of our apparatus, there may be obtained 

 even strong sparks. The electrophorus in this case might perhaps better deserve 

 the name of electrometer, or micro-electrometer, but Mr. V. rather calls it a 



