ALBUMENS AND OTHER ORGANIC SUBSTANCES. CREIGHTON. 67 



chloric acid was added to throw down a white precipitate. The 

 precipitate was filtered off and small portions of the filtrate were 

 tested with ammonium ferrous sulphate, and haematoxjiin. The 

 former gave a deep blue precipitate, but no reaction occurred 

 with the latter reagent. To the remainder of the filtrate more 

 hydrochloric acid was added, but no further precipitation took 

 place; on boiling, however, a white precipitate separated from 

 the solution. It was found that the light yellow filtrate from 

 this precipitate could l>e boiled without further precipitation 

 taking place. To the cooled filtrate a few drops of ammonium 

 ferrous sulphate were then added. The solution turned blue, and 

 on standing a deep blue precipitate separated out ; on boiling the 

 solution the precipitate became flocculent, resembling a precipi- 

 tate of aluminium hydroxide. The precipitate when heated on 

 a platinum foil charred at a low temperature. This precipitate 

 could not have consisted of simply Tumbull's blue ; for when 

 ammonium ferrous sulphate was added to a hydrochloric acid 

 solution of potassium ferricyanide having the same degree of 

 yellow colour as the above filtrate, and the mixture boiled, the 

 precii^itate which separated out was not flocculent, but finely 

 divided. Moreover, on allowing it to settle and pouring off the 

 supernatant liquid the blue precipitate was found to dissolve 

 in water. The results of this experiment suggest the formation 

 of a complex by the iron salt and albumen, which is stable 

 towards heat, and which is precipitated by ammonium ferrous 

 sulphate. 



Like ferric chloride, potassium ferricyanide increases the 

 coagulation temperature of albumen. A solution of potassium 

 ferricyanide and white of egg, of one half the concentration 

 previously employed, first became turbid at 64.5° ; while a pure 

 white of egg solution, of the same concentration, became cloudy 

 at 61.5°. When, besides the potassium ferricyanide and white 

 of egg, a very small quantity of ammonium ferrous sulphate 

 was present in the solution, coagulation did not take place 

 below 75°. 



