On Sal Nitrum and Nitro- Aerial Spirit 95 



bell-jar may be at the same level as the water outside, 

 as may be done by means of a syphon, the form 

 and mode of use of which were described in the 

 preceding chapter. Then let the water outside be 

 drawn off until it is lower than the water inside by 

 about three finger-breadths. And let everything 

 remain thus until the air enclosed in the glass, heated 

 by the hands of the operator, has returned to its former 

 state. And then, lastly, let the height of the water 

 within be noted by papers attached here and there to 

 the outer surface of the glass, as is shown in the 

 aforesaid figure. 



And now let the aforesaid small pieces of iron be 

 lowered by means of the string, the end of which 

 hangs outside, into the vessel which contains the 

 spirit of nitre. And so a very intense action will 

 soon be excited and the water within will at once be 

 depressed by the vapours thence arising. 



After action of this sort has gone on for the third 

 part of an hour more or less, or rather when the 

 water within has been depressed about three finger- 

 breadths by the vapours produced, let the pieces of iron 

 be lifted out of the vessel by means of the aforesaid 

 string. This done, after a short time you will see the 

 water within gradually rising, and in the course of an 

 hour or two you will see it far above the height first 

 marked. For the water which was quickly depressed 

 by the aforesaid vapours about three finger-breadths 

 below the point first marked, now rises some three 

 finger-breadths more or less above it ; so that about 

 a fourth part of the space in the glass which was 

 previously occupied by air is now occupied by the 

 water rising within. And indeed the water which has 

 risen in this way in the glass will not, even after a long 

 time, fall to the original mark. 



