20 Dr. Hofmann on the true Composition of Chlorindatmit. 



Copper duplicates of steel or copper engravings, it is well 

 known, are not nearly so durable as the original plates, yet 

 in some cases they may be advantageously employed, — not 

 however where very large numbers are likely to be required, 

 as, for example, in the printing of bank notes. I was once 

 consulted as to the practicability of coating the interior of the 

 air-pumps and the valve facings of large marine engines by the 

 electro-metallurgic process, and I include this as one of the 

 improper applications of the art. In conclusion, I again re- 

 peat, that the processes of electro-metallurgy are a valuable 

 acquisition to the arts, yet it is necessary to bear in mind its 

 defects, in order that we may not apply it to purposes for 

 which it is unfitted. 



V. On the true Composition of Chlorindatmit. 

 By August Wilhelm Hofmann, Ph.D.^ 



IN a preceding memoir on the Metamorphoses of Indigo, 

 I have described under the name of trichloraniline a body 

 which may be regarded as aniline, in which three equivalents 

 of hydrogen are replaced by an equal number of chlorine : 

 Aniline . . . rrCjgHyN 



Trichloraniline . =Ci2< pf >N. 



I had already, a year and a half ago, observed the forma- 

 tion of this body by the action of chlorine on aniline t, but at 

 that time the quantity obtained was so small that I was 

 obliged to content myself with a conjectural opinion of its con- 

 stitution. More lately I found that the same substance was 

 produced by the treatment of chloraniline with chlorine. Even 

 by the last-mentioned way the quantity obtained was but 

 small. With all my efforts I could not obtain more than 

 was just sufficient for one combustion, which unfortunately 

 gave somewhat too much carbon J. Although myself tho- 

 roughly convinced of the exactness of the given formula, — 

 the method of formation of this body, the complete ana- 

 logy with tribromaniline and chlorodibromaniline, indepen- 

 dently of the analysis adduced, being sufficient evidences, — I 

 thought it however desirable to place the composition of tri- 

 chloraniline beyond every doubt by the production of better 

 numbers. 



At first I thought of obtaining these numbers by a repeti- 



* Communicated by the Chemical Society: having been read February 



17,1845. y> b 



t Liebig's y4n7i. vol. xlvii. p. 68, and Phil. Mag. S. 3. vol. xxvi. p. 199. 

 X See the preceding Memoir. 



