DESTRUCTIVE DISTILLATION OF ANIMAL SUBSTANCES. 207 



DlPYRIDINE. 



The substance so obtained is a base to which, for reasons that will be imme- 

 diately apparent, I give the name of dipyridine. It forms white crystals fusing 

 at 108° Cent., and solidifies on cooling into a crystalline mass. It volatilises slowly 

 at 100°, and sublimes unchanged at a high temperature, giving long needle-shaped 

 crystals. It is rather sparingly soluble in cold but readily in boiling water, and 

 the fluid, on cooling, becomes filled with a mass of interlaced needles. It is readily 

 soluble in alcohol and ether, and the boiling solutions give acicular crystals on 

 cooling. It likewise dissolves in pyridine and in volatile oils. From the oily base 

 along with which it distils in the first process of preparation, it crystallises in 

 short, thick, four-sided prisms, which are transparent so long as they remain in 

 the fluid, but soon become opaque when they are removed from it. When well 

 purified they are inodorous, but in general they have a faint smell, due, apparently, 

 to a trace of the fluid base adhering to them. Dipyridine is a very stable com- 

 pound. It is not decomposed by hydrochloric, sulphuric, or nitric acids. Potash 

 and ammonia precipitate it from its solutions in acids as a mass of minute crystals. 

 Its aqueous solution gives no precipitates with solutions of sulphate of magnesia, 

 zinc, nickel, acetate of lead, or perchloride of iron. With sulphate of copper it 

 gives a pale bluish-white precipitate, with corrosive sublimate a white amorphous 

 powder insoluble in boiling water, and with nitrate of silver a white precipitate 

 insoluble in cold and sparingly in boiling water, from which the compound is 

 obtained in crystals on cooling. Its most characteristic reactions, however, are 

 those it gives with the ferro- and ferri-cyanides of potassium. If a few drops of the 

 ferrocyanide of potassium be added to a not too dilute solution of the dipyridine 

 hydrochlorate, a pale precipitate makes its appearance, which rapidly changes to 

 a dirty indigo colour, increasing at the same time in quantity. If the proper 

 concentration is hit, the precipitate consists entirely of very minute needle-shaped 

 crystals having a dark indigo colour. They dissolve in boiling water, forming a 

 very deep and rather dull purple solution, and are again deposited on cooling ; 

 but if the boiling be continued for some time, the compound appears to undergo 

 some change, for the fluid retains its red colour at ordinary temperatures, though 

 a great part of the substance is still deposited in crystals. A saturated cold 

 solution of dipyridine in water gives no precipitate with ferrocyanide of potassium, 

 but on the addition to the mixture of a drop or two of hydrochloric acid the dark 

 precipitate instantly makes its appearance, and is deposited in small crystals. The 

 precipitate is readily soluble in excess of hydrochloric acid. When ferri cyanide 

 of potassium is added to dipyridine hydrochlorate no immediate effect is observed, 

 but on standing, the interior of the test-tube becomes lined with minute prisms of 

 sulphur yellow colour and high lustre. If the solution be boiled, it acquires a 

 dark colour, and partial decomposition takes place. 



