Compound Cellulo-ses 129 



that it is not appreciably affected by the presence of oxidising 

 agents such as chromic acid. 



The alternative conclusion is that it is due to a coagulation 

 or precipitation of the ferric ferricyanide by the fibre-substance, 

 in the first instance, followed by a rearrangement of its con- 

 stituents by specific combination with the fibre constituents. 



Collateral evidence in support of this view is afforded by 

 the behaviour of the ferricyanide with another typical colloid, 

 viz. gelatin. Solutions of gelatin give with the ferric ferri- 

 cyanide a voluminous coagulum of a greenish colour, and the 

 reaction is approximately a quantitative one, but of course 

 depending to some extent upon the conditions of precipitation. 

 The following relations were determined : 



One series of experiments 



A white gelatin (containing 16*5 p.ct. hygroscopic mois- 

 ture and 2-86 p.ct. ash constituents) was weighed out in 

 quantities of 2 grms. (=1-613 dry and ash-free gelatin) and 

 dissolved. The solutions were variously diluted and treated 

 with half decinormal solution of the ferric ferricyanide added 

 from a burette. 



(1) To completely precipitate in the cold 23 c.c. were 

 required. 



(2) To completely precipitate at 50 C. 24*5 were required 



(3) To a third quantity 32 c.c. of the ferricyanide solution 

 were added. 



The precipitates were collected, dried, and weighed ; the 

 weights were: (i) 1*990; (2) 2-031; and (3) 2-077 respec- 

 tively. The mean weight 2*032 shows an increase of weight 

 of 21-6 p.ct. An estimation of Fe 2 O 3 in the product gave 

 6-0 p.ct., the proportion being rather lower than in the 

 case of the fibre-cyanide product, which, with the same gain 

 in weight, contains 7 p.ct. Fe 2 O 3 . The coagulum is in this 

 case, however, only slightly blue, darkening gradually on 



