﻿Intelligence and Miscellaneous Articles. 313 



Table A will serve to construct Table B ; this latter gives the 

 length x which a column of nitrous vapour at 26°* 7 must have, on 

 our hypothesis, to present the same degree of colour, as a column 

 of vapour of constant length and equal to unity but of varying tem- 

 perature. It is calculated by the formula 



— « I , 



D 3-1214x20-26 

 in which P is the weight of the unit of volume of peroxide of ni- 

 trogen at t degrees. It will be seen from an inspection of this Table 



that the coloration at first rapidly increases with the temperature 



that it then attains a maximum, because the increase in specific co- 

 loration is balanced by a decrease in density— that, finally, the effect 

 of this decrease predominates, so that the coloration itself decreases 

 indefinitely. 







A. 



1 



B. 





Tempera- 











ture, 



Weight of 



Proportion in 



Theoretical 





t. 



a litre of 



weight of NO 2 , 



coloration, 



Experimental 





vapour, 

 P. 



a 



\a P 



numbers. 



D 31214x20-26 



267 



31214 



20-26 per cent. 



1 



1 



35-4 



2-8975 



25-8 „ 



1 182 



118 



39-8 



27745 



296 



1-299 



1 28 



49-6 



2-4793 



40-5 



1-588 





60-2 



21980 



53-3 



1-852 



1-9 



700 



1-9768 



661 



2066 





80-6 



1-7973 



76-9 



2- 185 



2-2 



900 



1-6744 



851 



2-253 





1001 



1-5892 



89-7 



2-254 



23 



111-3 



1-5144 



93-3 



2-234 



2-25 



121-5 



1-4519 



96-6 „ 



2-218 



2-24 



135 



1-3814 



99-1 



2165 



2-2 



1540 



1-3082 



101-7 „ 



2104 



212 



200 







1-9 



1-95 

 1-6 



225 

 250 

 275 







1-8 

 1-7 

 1-6 







300 







1-56 



1-52 





These consequences of our hypothesis have been experimentally 

 verified. By means of a special calorimeter we determined the values 

 of x with a sufficient degree of approximation ; the means of the 

 experiments are met with in the last column of Table B. We 

 have carried the experiment beyond the temperatures for which the 

 vapour-density has been determined by MM. Deville and Troost ; 

 we have assumed with these chemists that the density is then normal! 



Our apparatus consists of two prisms for total reflection, which 

 send the light of the zenith through two horizontal tubes closed by 

 glass plates and placed in the same right line. These tubes contain 

 vapours under the ordinary atmospheric pressure ; they are heated 



