126 CHAPTER IX. 



submitted to the next stage of the hardening process. (If 

 the mass is found to be not quite hard enough to come away 

 safely, it should be put for a day or two into weak alcohol, 

 30 to 70 per cent.) 



157. Hardening, Definitive. Several methods are available 

 for the definitive hardening process. One of these is the 

 chloroform method, due to VIALLANKS (Rech. sur I' Hist, et le 

 Dev. des Inwctes, 1883, p. 129). I recommend this method 

 for small objects, because I find it much more rapid than the 

 alcohol method, whilst giving at least as good a consistency 

 to the mass. For large objects the method is said by some 

 writers to be inferior to the alcohol method, because the 

 rapid hardening of the external layers is an obstacle to the 

 diffusion necessary to the hardening of the inner layers. 



The method consists in bringing the objects into chloro- 

 form. 



Under the influence of this reagent the collodion coagu- 

 lates rapidly into a mass having the consistency of wax. 



In some cases a few hours' immersion is sufficient to give 

 the requisite consistence. In no case have my specimens 

 required more than three days. But the length of time 

 required varies in a very inexplicable way, so that no rule 

 can be given. The collodion frequently becomes opaque on 

 being put into the chloroform, but regains ifcs transparency 

 after a time. 



Small objects may be hardened by chloroform 'Without pre* 

 liminary hardening by evaporation. All that is necessary is 

 to expose the mass to the air for a few seconds until a mem- 

 brane has formed on it, and then bring it into chloroform. 

 If the mass is in a test-tube this may be filled up with 

 chloroform, and left for two or three days if need be. By 

 this time the collodion mass will be considerably hardened, 

 and also somewhat shrunk, so that it can be shaken out of ; 

 the tube. It is then brought into fresh chloroform in a 

 larger vessel, where it remains for a few more days until it 

 is ready for cutting. But sufficient hardening is sometimes 

 obtained in a few hours. 



Good chloroform is a necessity, as the reaction cannot be 

 obtained with samples of chloroform that are not free from 

 water. 



