VOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. 521 



impregnated, and not the nitrous. Still however some acid is the constant 

 result of the union of the two kinds of air, and not water only. A quantity of 

 the same precipitate per se yielded no fixed air by heat. Comparing this experi- 

 ment with that in which iron is ignited in dephlogisticated air, this general con- 

 clusion may be drawn, viz. that when either inflammable or dephlogisticated air 

 is extracted from any substance in contact with the other kind of air, so that 

 one of them is made to unite with the other in what may be called its nascent 

 state, the result will be fixed air; but that if both of them be completely 

 formed before their union, the result will be nitrous acid. 



It has been said, that the fixed air produced in both these experiments may 

 come from the plumbago in the iron from which the inflammable air is obtained. 

 But since we ascertain the quantity of plumbago contained in iron by what re- 

 mains after its solution in acids, it is in the highest degree improbable, that 

 whatever plumbago there may be in iron, any part of it should enter into the 

 inflammable air procured from it. Besides, according to the antiphlogistic 

 hypothesis, all inflammable air comes from water only. As it cannot be said, 

 that any real fixed air is found in inflammable air from iron (since it is not dis- 

 coverable by lime-water) it must be supposed, that the elements, or component 

 parts of fixed air are in it ; but one of these elements is pure air, and the mix- 

 ture of nitrous air shows that it contains no such thing, though, according to 

 M. Lavoisier, fixed air contains 7*2 parts in 100 of pure air. 



However, being apprized of this objection to inflammable air from iron, I 

 made use of inflammable air from tin, and I had the same result as with that 

 from iron. I also calculated the weight of the fixed air which I got in the pro- 

 cess, and comparing it with the plumbago which the iron necessary to make the 

 inflammable could have contained, I found that in all the cases it far exceeded 

 the weight of the plumbago ; so that it was absolutely impossible, that the fixed 

 air which I found should have had this origin. For the greater satisfaction. Dr. 

 P. recites the particulars of a few experiments of this kind. But, for these, we 

 must refer to a separate pamphlet which Dr. P. published on this subject. 



HI. Observations on the Class of Animals called^ by Linnceus, Amphibia ; par- 

 ticularly on the Means oj Distinguishing those Serpents which are Venomous^ 

 Jrom those which are not so. By Edward Whitaker Gray, M. D., F. R. S. 

 p. 21. 



Of the various classes of the animal kingdom, says Dr. G., no one has been 

 so little attended to as the class, called by Linnaeus, Amphibia. What he him- 

 self did in that class, though far superior to what any other person has done, 

 was evidently done in a hurry ; false references are at least as common in that as 

 in any other part of his works, and many of his descriptions are given in a ytry 



YOL. XVI. 3 X 



