COMBUSTIBILITY OF GASES. 
31 
if ids are much denser than hydrogen gas. It is possible that The colour 
the conducting power as to electricity, which must be peculiar p^g 0 ^ ^ 
to each gas, may be concerned in this effect ; and Priestley sup- conducting 
poses, not, perhaps, without reason, that the red colour may be P ower °* tiie 
an indication that the electricity is transmitted with diffi- 
culty. 
In the vapor of boiling water the electric spark is of an j n steam the 
orange yellow, and in dried carbonic gas, as well as in oxigen spark is yel- 
gas, I have always seen it of a very beautiful violet. 
In order to dry these gases as much as possible, I hay 6 left 
them to remain over pure lime a little heated, which absorbed 
the water of the carbonic acid until it was saturated. 
We see, therefore, in these experiments, the electric light ap- All the prisma- 
pears with the colours of the solar spectrum red, orange, seen in 0 ^j^ re 
green, blue, and sometimes violet, a phenomenon which agrees rent sparks, 
with the observations of Ritter. This philosopher applied the 
positive pole of the pile to his eye, while he brought his hand 
into contact with the negative pole, and he observed that ob- 
jects then appeared to him brighter and bluish j but, on the Voltaic specu- 
contrary, when he applied the negative pole to his eye, objects Iat *oiis. 
became deeper and of a reddish colour. (See Gilbert’s An- 
nals, VII, p. 447.) When the carbonates dissolved in water, 
or even pure water, is exposed to the current of the voltaic 
pile, a decomposition takes place ; the carbonic acid, or the 
pure oxigen is separated by the positive pole, and it is precisely 
in these two gases that the electric spark appears blue 5 but it 
appears red in hydrogen gas, phosphorated hydrogen, ammo- 
nia, sulphurated hydrogen, and probably in all the gases which 
are disengaged at the negative pole*. 
14. In atmospheric air, which I had compressed by a co- Electric spark 
lumn of two feet of mercury, I caused the electric spark to 
pass. The spark was brighter, but ne>t^oloured. It is weaker a i r . 
in hydrogen and in ratified air. From these observations, I 
think it may be concluded, that the intensity of the electric 
* From some experiments, not yet sufficiently repeated, I think there 
is reasouto conclude, that the colour of the electric spark is governed 
by the refracting power of the medium upon light ; that at the maxi- 
mum the colour is red, and at the minimum violet. Note of M, 
^chweigger. 
light 
