ON ORGANIC COLOURING MATTERS. 485 



smaller open tube was afterwards attached to each side of the larger one, near to 

 its shut end, so as to communicate with its cavity. These lateral tubes projected 

 for a short distance at right angles to the long axis of the larger tube, and then 

 ran parallel to it, with their open mouths pointing in the opposite direction from 

 that of the single canal at the other end of the tube. To prevent confusion, I 

 shall call the lateral appendages which I have described, the horns of the tube. 



When the latter was arranged for an experiment, the narrowed termination 

 at one end was placed in communication with a short tube filled with chloride 

 of calcium, by means of a caoutchouc connector. The free extremity of this tube 

 was bent at right angles, and dipped into oil, so as to cut off communication with 

 the outer air. To each of the open horns, also, a chloride of calcium tube, three 

 feet in length, was attached. The one of these tubes was intended to convey, 

 and render anhydrous, a current of air, which should dry the paper. The other, 

 in like manner, was to carry and dry the gas, which should be brought in contact 

 with the paper, when the latter was deprived of moisture. At the beginning of 

 an experiment, the tube through which the gas subsequently passed, after being 

 connected with one of the horns, was sealed at the end furthest from the paper. 

 Its presence from the first was essential, because otherwise the dried paper must 

 have been put in communication with the moist outer air, when a fresh chloride 

 of calcium tube to carry the gas was substituted for that Avhich previously con- 

 veyed the air : for if the same tube in whole, or in part, had been employed, first 

 to dry the air, and then the gas, the freedom of the latter from moisture could 

 not have been counted upon. 



I found, after trying various devices, a pair of common bellows the most con- 

 venient instrument for furnishing a current of air. The air was first passed 

 through a bulbed tube, immersed in a freezing mixture, and then through the 

 chloride of calcium tube into the one containing the paper ; from which it escaped 

 through the smaller drying tube that dipped into oil, as already mentioned. The 

 paper was maintained by gas lights at a temperature of about 220" Fahr., and 

 the air was kept passing over it, for at least two, generally for three, hours. 



When the paper appeared perfectly free from moisture, the lateral horn, by 

 which the air reached it, was sealed at the blow-pipe, and the drying apparatus 

 detached. The shut end of the other long chloride of calcium tube was then 

 opened, and connected with an apparatus for furnishing the gas to be used in the 

 experiment. 



The woodcut on the following page wiU make the description more intelligible. 

 Only the more essential parts of the arrangement are represented in the dia- 

 gram ; the bellows and connecting flexible tube on the one hand, and the retort 

 in which the gas was generated on the other, as well as the washing bottles, &c., 

 being omitted. 



