THE ALUMNI JOURNAL. 



301 



the negative side of the plate, but were 

 absent from the positive side, while on 

 the positive side of the plate there was 

 the positive pole spectrum of nitrogen, 

 and on the negative side of the plate the 

 negative pole spectrum of nitrogen and 

 the hydrogen spectrum. 



Sulphur Monochloride. — When the tube 

 was filled with the vapor of this substance 

 at a low pressure, the chlorine lines were 

 brighter on the negative side of the plate 

 than at the positive, while the sulphur 

 lines were brighter at the positive side 

 than at the negative. Thus the chlorine 

 in this substance behaves in the opposite 

 way to the chlorine in HC1; in the latter 

 compound the chlorine ion has a charge 

 of negative electricity, while in the sul- 

 phur monochloride it has a charge of 

 positive electricity. 



Influence of the Chemical Constitution of 

 a Compoimd on the Sign of the Charge of 

 Electricity on one of its Constituent Atoms. 

 — In many organic compounds an atom 

 of the electro -positive element hydrogen 

 can be replaced by an atom of the electro- 

 negative element chlorine without alter- 

 ing the type of the compound. Thus, 

 for example, we can replace the four hy- 

 drogen atoms in CH 4 by chlorine atoms, 

 getting successively the compound CH S 

 CI, CH 2 C1 2 , CHCI3, and CC1 4 . It seemed 

 of interest to investigate what was the 

 sign of the change of electricity on the 

 chlorine atom in these compounds. The 

 point is of some historical interest, as the 

 possibility of substituting an elect: o- 

 negative element in a compound for an 

 electro-positive one was one of the chief 

 objections assigned against the electro- 

 chemical theory of Berzelius. 



"When the vapor of chloroform, CHC1 8 , 

 was placed in the tube, it was found that 

 both the hydrogen and the chlorine lines 

 were bright on the negative side of the 

 plate, while they were absent from the 



positive side, and that any increase in 

 the brightness of the hydrogen lines was 

 accompanied by an increase in the 

 brightness of those due to chlorine. 

 The spectium on the positive side of the 

 plate was that called the carbonic oxide 

 spectrum; when first the discharge passed 

 through the tube, the spectrum on the 

 positive side was the so-called candle 

 spectrum, but this very rapidly changed 

 to the carbonic oxide spectrum. The 

 appearance of the hydrogen and chlorine 

 spectra at the same side of the plate was 

 also observed in methylene chloride and 

 in ethylene chloride. Even when all the 

 hydrogen in CH 4 was replaced by chlor- 

 ine, as in carbon tetrachloride, CC1 41 the 

 chlorine spectra still clung to the negative 

 side of the plate. To test the point, still 

 further, I tried the analogus compound 

 silicon tetrachloride, inserting a small jar 

 in the circuit to brighten the spectrum. 

 The chlorine spectrum was again bright- 

 est at the negative side of the plate, while 

 the silicon spectrum was brightest at the 

 positive. This is a very favorable case 

 for the application ot this method, as 

 there are two silicon lines (wave-lengths 

 5058, 5043) quite close to two chlorine 

 ones (wave-lengths 5102, 5078), so that 

 their relative brightness can easily be 

 compared. The experiment with the sili- 

 con tetrachloride is more conclusive than 

 those with the carbon compounds, as 

 with the latter the spectrum on the posi- 

 tive side of the plate is a band spectrum, 

 and since the potential gradient when the 

 discharge is passing very much steeper 

 on the negative side of the plate than on 

 the positive, the effects observed might 

 be supposed to be due to the circum- 

 stances on the negative side being better 

 adapted for the production of the line 

 spectra than those on the positive. This 

 explanation is not, however, applicable 

 to the case of silicon tetrachloride, where 



