80 



PARTICULAR PHENOMENA EXHIBITED BY CHLORINE AND HYDROGEN. 



through contraction of the sentient gases, was now determined. These numbers are 

 contained in the following table. In one column is given the number of each divis- 

 ion ; in the adjacent one, the period of contraction through it. 



Let us now take these observations and project them, as is done in Jig. 125, the 

 amount of contraction representing the quantities of gases that have united being laid 

 off on the axis of abscissas, the times on the ordinates. But these times represent the 

 number of rays which have fallen on the sentient mixture ; consequently, the ordinates 

 of that curve represent the quantities of tithonic rays, and the abscissas the corre- 

 sponding chemical effects. 



307. Inspection of the curve shows its peculiarities at once. We see that after the 

 first preliminary expansion has taken place, expressed by that portion between a and l>, 

 for a certain space of time, although rays are constantly falling on the mixture and be- 

 ing absorbed, no visible effect is produced, there being neither expansion nor contraction, 

 as is shown by b c. A certain space of time, amounting in this instance to 270 seconds, 

 being now accomplished, contraction, from union of the gases, begins. In that portion 

 of the curve c d which represents the progress of the phenomenon, the curvature is per- 

 petually diminishing, and at d approaches sensibly to a straight line. From d to e, which 

 includes the remainder of the observations, the line preserves its rectilinear character. 



308. The study of the properties of this curve, or of the tabular numbers, serves to 

 prove that when chlorine and hydrogen unite under the influence of the tithonic rays, 

 there are four distinct periods of action. 



1st. For a brief space the mixture expands. 



2d. For a much longer period it then remains wholly stationary, neither expanding 

 nor contracting, although the rays are constantly falling on it and it is absorbing them. 



3. Contraction arising from the production of muriatic acid begins, commencing at 

 first slowly, then more and more rapidly. 



4th. And after that contraction has fairly set in, it goes on with uniformity, equal 

 quantities of muriatic acid being produced in equal times by the action of equal quan- 

 tities of the rays. 



309. If, therefore, it is permitted us to generalize from this case of the action of rays 

 on one of the most sensitive substances known, a mixture of chlorine and hydrogen, we 



