DESCRIPTION OF THE EXPERIMENT. 



processes are best carried on in a small porcelain or earthenware trough, filled with a 

 saturated solution of common salt, which dissolves chlori'ne slowly ; and to avoid ex- 

 plosions, operate on limited quantities of the gases. Tubes that are eight inches long 

 and half an inch in diameter will answer very well. The two tubes now contain the 

 same gaseous mixture, and only differ in the circumstance that one is tithonized and 

 the other not. Place them, therefore, side by side before a window, through which the 

 entrance of daylight can be regulated by opening the shutter ; and now, if this part of 

 the process is conducted properly, it will be seen that the tithonized chlorine com- 

 mences to unite with the hydrogen, and the salt water rises in that tube. But the un 

 tithonized chlorine shows no disposition to unite with its hydrogen, and the liquid in 

 its tube remains motionless for a long time. Finally, as it becomes slowly tithonized 

 by the action of the daylight impinging on it, union at last takes place. From this, 

 therefore, we perceive that chlorine which has been exposed to the sun will unite 

 promptly and energetically with hydrogen ; but chlorine that has been made and kept 

 in the dark shows no such property. 



902. As I doubt not this remarkable experiment will be repeated by chemists, I will 

 add that the only point to which attention in particular is to be given, is in the final 

 exposure to the light. This must not be too feeble, or the action will be tedious ; but 

 the direct sunbeam must be sedulously excluded, or an explosion will result. A room 

 illuminated by one small window, looking to the north, answers very well. It need 

 scarcely be added, that care must be taken that both tubes are illuminated alike. 



II. The Change in the Chlorine is not Transient. 



903. Now it might be supposed that this apparent exaltation of the electro-negative 

 properties of the chlorine is only a transient thing which would speedily pass away, 

 the gas reverting to its original untithonized condition. 



904. To show that this is not so, tithonize some chlorine in a tube as before. Place 

 it for an hour or two in the dark along with the tube of untithonized chlorine, with 

 which it is to be compared ; then to both add hydrogen. Expose them, as in the for- 

 mer experiment, to the daylight, and the result will turn out as before, the tithonized 

 chlorine forming muriatic acid at once, and the untithonized refusing to do so. 



905. This, therefore, shows that the change which the sunbeams impress upon 

 chlorine is to a certain extent a permanent change, and, unlike a calorific effect, it does 

 not spontaneously and rapidly pass away. 



III. There are two Stages in the Phenomenon. 



906. Let us now proceed to make an inquiry into the nature of the change thus im- 

 pressed on the chlorine. This, I shall show, rests in the circumstance of the absorption 

 of rays which correspond in refrangibility to the indigo, and which appear to become 

 latent. 



907. In a tube, over salt water, mix together equal volumes of untithonized chlorine 

 and hydrogen gas. Expose it to the daylight, marking the time at which the exposure 

 commences. Watch the level of the liquid in the tube narrowly, and, though station- 



