VOL. X.] PHILOSOPHICAL TRANSACTIONS. 241 



the mixture of aquafortis and copper,* remains always air, and always keeps up 

 the water in the glass at that height to which it first raised it ; but on the con- 

 trary, the air produced by the mixture of oil of tartar and oil of vitriol,-|- almost 

 all vanishes of itself in 24 hours. — On mixing equal parts of aquafortis and aqua- 

 vitas, and putting two equal quantities of the mixture in two small glasses, with 

 two equal bits of iron, one in each, and including one of the glasses in vacuo, 

 there was seen a very great ebullition, and the liquor became black ; whilst the 

 other glass that was left without the receiver, made no ebullition, but remained 

 always transparent, or rather white than black. After these two glasses had 

 stood 1 2 hours, the iron in the glass in vacuo was almost all dissolved, whereas 

 the other was very little diminished. This experiment succeeds quite the con- 

 trary when made with aquafortis alone and copper ; for then the solution is less 

 within the vacuum than without it. 



Oil of olives makes no ebullition, neither with vinegar nor with spirit of wine, 

 when they are just mixed, either in vacuo or out of it. But having mixed to- 

 gether without the receiver, some of that oil and vinegar and spirit of wine, and 

 put this mixture in vacuo, it did not boil up so soon as when there was no oil ; 

 but then the bubbles, which it afterwards made were larger, and they began to 

 appear again from time to time, so that some of them were seen a quarter of an 

 hour after the receiver had been exhausted. Possibly this may be owing to the 

 oil swimming on the top, retaining the more volatile parts of the spirit of wine, 

 which would otherwise fly away as soon as the air is begun to be pumped out, 

 and at the same time hinders the surface of the liquor below from easily rising 

 up into bubbles; because to make them do so, the parts of the oil that stick 

 close to each other must be separated. When therefore the volatile parts are col- 

 lected in a sufficient quantity, able to surmount the resistance which the oil makes 

 to it, they issue out with greater violence than if nothing had detained them. 



All these ebullitions hitherto spoken of, are greater in vacuo than in the 

 open air : but it is not so with lime. For taking two equal glasses with two 

 equal quantities of water, and putting the one of them in vacuo, the other in 

 the open air, there was let fall into both at the same time two equal parcels of 

 lime, one into each ; and it appeared, that that which was in vacuo did indeed 

 throw up some large bubbles, but yet fewer of them than that which was in the 

 air : and having taken it an hour after out of the receiver, and stirred the lime, 



* The aeriform body thus produced by die action of aquafortis on copper, was nitrom gas. It 

 appears, therefore, tliat the discovery of this species of permanently elastic fluid is due to the authors 

 of the above related experiments, to which Mr. Boyle's previous pneumatical inquiries had served as 

 a clue. 



-}• Fixed air or carbonic acid gas, 



VOL. II. I I 



