94 
These observations led me to conclude that the effect was 
due to hydrogen, and not to acid as Mr. Johnson appeared 
to think, having entered into combination with the iron 
during its immersion in the acid, which hydrogen gradually 
passed off when the iron was exposed. 
It was obvious however that this conclusion was capable 
of being further tested. It was clearly possible to ascer- 
tain whether or not the gas was hydrogen ; and whether 
hydrogen penetrated iron when under the action of acid. 
With a view to do this I made the following experiments. 
First, however, I would mention that after 24 hours I 
examined what remained of the wire, when I found that all 
appearance of frothing had vanished and the wire liad reco- 
vered its ductility, so much so that it would now bend 
backwards and forwards two or thi’ee times without break- 
ing, whereas on the previous evening a single bend had 
sufficed to break it. 
I then obtained a piece of wrought iron gas pipe 6 inches 
long and | inch external diameter, and rather more than 
-Je of an inch thick ; I had this cleaned in a lathe both 
inside and outside ; over one end I soldered a piece of cop- 
per so as to stop it, and the other I connected with a piece 
of glass tube by means of indiarubber tube. I then filled 
both the glass and iron tubes with olive oil and immersed 
the iron tube in diluted sulphuric acid which had been 
mixed for some time and was cold. Under this arrange- 
ment any hydrogen which came from the inside of the glass 
tube must have passed through the iron. 
After the iron had been in the acid about 5 minutes 
small bubbles began to pass up the glass tube. These were 
caught at the top and were subsequently burnt and proved 
to be hydrogen. At first, however, they came off but very 
slowly, and it was several hours before I had collected enough 
to burn. With a view to increase the speed I changed the 
acid several times without much effect until I happened to 
