160 FARADAY 



acid, which is the acid you might have to use !f you were 

 to make these experiments (only, in using this acid with 

 limestone, the body that is produced is an insoluble sub- 

 stance, whereas the muriatic acid produces a soluble sub- 

 stance that does not so much thicken the water). And you 

 will seek out a reason why I take this kind of apparatus for 

 the purpose of showing this experiment. I do it because 

 you may repeat in a small way what I am about to do in a 

 large one. You will have here just the same kind of action ; 

 and I am evolving in this large jar carbonic acid exactly 

 the same in its nature and properties as the gas which we 

 obtained from the combustion of the candle in the atmos- 

 phere. And, no matter how different the two methods by 

 which we prepare this carbonic acid, you will see, when we 

 get to the end of our subject, that it is all exactly the same, 

 whether prepared in the one way or in the other. 



We will now proceed to the next experiment with regard 

 to this gas. What is its nature ? Here is one of the vessels 

 full, and we will try it as we have done so many other gases 

 by combustion. You see it is not combustible, nor does it 

 support combustion. Neither, as we know, does it dissolve 

 much in water, because we collect it over water very easily. 

 Then you know that it has an effect, and becomes white in 

 contact with lime-water; and when it does become white 

 in that way, it becomes one of the constituents to make car- 

 bonate of lime or limestone. 



The next thing I must show you is that it really does dis- 

 solve a little in water, and therefore that it is unlike oxygen 

 and hydrogen in that respect. I have here an apparatus by 

 which we can produce this solution. In the lower part of 

 this apparatus is marble and acid, and in the upper part cold 

 water. The valves are so arranged that the gas can get 

 from one to the other, I will set it in action now, and you 

 can see the gas bubbling up through the water, as it has been 

 doing all night long, and by this time we shall find that we 

 have this substance dissolved in the water. III take a glass 

 and draw off some of the water, I find that it tastes a little 

 acid to the mouth ; it is impregnated with carbonic acid ; and 

 if I now apply a little lime-water to it, that will give us a 

 test of its presence. This water will make the lime-water 



