240 Sir J. J. Thomson oh 



atom and molecule of oxygen. Rays with the?e atomic 

 weights and having a negative charge are very conspicuous, 

 their only rival on the negative side being the hydrogen 

 atom. A copy of the photograph taken with oxygen at a 

 very low pressure in the tube is given in fig. 16. 



Carbonic Oxide. 



The electric atomic weights of the characteristic primary 

 rays for carbonic acid are 12, the carbon atom with one 

 charge, 16 the oxygen atom, 32 the oxygen molecule, and 

 one with an atomic weight about 47, this may be a molecule 

 of ozone which would have an atomic weight 48, or possibly 

 one of carbonic acid which would have an atomic weight of 

 44. It would thus appear that the molecule of CO does not 

 appear among the positive rays when the discharge passes 

 through this gas. Fig. 18 is a photograph for this gas. 



Marsh- Gas. 



The electric atomic weights are 16, the molecule CH 4 more 

 probably than the atom of oxygen, as it does not appear on 

 the negative side, and 2S. This may possibly be a molecule 

 of acetylene 2 H 2 , which would give an atomic weight of 

 26. It is remarkable that there were no lines with an atomic 

 weight of 12 on this plate, though it was present in the 

 other carbon compounds which were investigated, carbonic 

 oxide and cyanogen. Fig. 19 is the photograph for this gas. 



Cyanogen. 



The electric atomic weights for the primary rays are 12, 

 the atom of carbon, and 26, the molecule CN. It is remark- 

 able that the latter is also found with a negative charge. 

 Fig. 20 represents the photograph for this gas. 



Helium. 



The line corresponding to the electric atomic weight 4, due 

 to the atom of helium, is exceedingly strong, and can be 

 detected when there is only a very small quantity of helium 

 in the discharge-tube. The most prominent line on fig. 21 

 is due to helium, the tube contained other gases in addition. 



Hydrochloric Acid Gas. 



The primary rays were the atom and molecule of hydrogen, 

 and a very faint one presumably due to the chlorine atom as 



