THOMSON'S METHOD OF CHEMICAL ANALYSIS 61 



A word of caution may well be given here in connexion with 

 the relative photographic intensities of the lines. These are 

 entirely misleading and incorrect, as one might very well expect 

 on seeing that in Plate I hydrogen gives almost the brightest 

 lines in a tube supposed to contain practically pure air. A trust- 

 worthy electrical method has been devised recently by which 

 the true relative intensities of the lines can be deduced from the 

 total charges carried by the particles which give rise to them ; 

 the results show that a hydrogen line appearing on the plate 

 or screen as the brightest line of the set may really not be one 

 hundredth part as intense as the lines corresponding to the gas 

 with which the tube is filled. 



From experiments already made by the electrical method, 

 we may say that roughly speaking the true intensities of lines 

 due to a given gas are proportional to the quantity of that gas 

 present, whilst the photographic intensity of lines of equal true 

 intensity is far greater in the case of those produced by particles 

 of lighter mass. 



To readers interested in chemistry a short description of the 

 specific behaviour of a few individual elementary substances 

 may be of interest. To begin with, it is a fact of the very first 

 importance to the student of the nature of electricity that up to 

 now, though every possible scrutiny has been applied, no positive 

 ray having a smaller mass than that associated with a hydrogen 

 atom has been detected. Elements of lower atomic weight, if 

 present, make no appearance on the sensitised surfaces used to 

 record the rays, neither does it seem possible for the hydrogen 

 atom itself to carry more than one charge. 



Hydrogen. — The lines due to H 1+ and H 2+ , largely no doubt 

 owing to their very exceptional photographic efficiency, appear 

 on practically every photograph taken of the part of the 

 magnetic spectrum which includes them. They can be elimin- 

 ated, however, by thoroughly rinsing out the tube with highly 

 purified oxygen. Oddly enough, considering the chemical 

 properties of the element, atomic hydrogen also appears 

 repeatedly with a negative charge, the negative parabola due 

 to the hydrogen atom being plainly visible in Plates I and 

 II. If hydrogen be mixed with a small percentage of some 

 other gas, such as nitrogen, a very remarkable line sometimes 

 makes its appearance which corresponds to a hypothetical 



