HARDENING. 161 



Watch-glasses, square porcelain water-colour moulds, and 

 the like, also make convenient imbedding receptacles. Care 

 should be taken to have them perfectly dry. Any of them) ~ 

 receptacles or supports may be set with the mass under a glass 

 shade, allowing of just enough communication with the air to 

 set up a slow evaporation. Or porcelain moulds or small 

 dishes may be covered with a lightly-fitting cover. 



294. Hardening. This is logically the next step, but as a 

 matter of fact is frequently begun before. For the different 

 processes of the collodion method so run into one another that 

 it is difficult to assign natural lines of demarcation between 

 them. 



The objects being imbedded, and in the stage at which we 

 left them at the end of 292, the treatment should be as 

 follows. As soon as the added thick collodion (of which only 

 just enough to cover the object should have been taken) has 

 so far sunk down that the object begins to lie dry, fresh thick 

 solution is added, and the whole is left as before. Provision 

 should be made for slow evaporation, either in one of the ways 

 above indicated, or, which is perhaps better, by setting the 

 objects under a hermetically fitting bell-jar, which is lifted for 

 a few seconds only once or twice a day. I have sometimes 

 found it advantageous to set the objects under a bell-jar 

 together with a dish containing alcohol ; so that the evapora- 

 tion is gone through in an atmosphere of alcohol. This is 

 especially indicated for very large objects. 



When the mass has attained a consistency such that the 

 ball of a finger no longer leaves an impress on it, it should be 

 scooped out of the dish or mould, or have the paper removed 

 if it has been imbedded in paper, and be 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.) 



Several methods are available for the definitive hardening 

 process. One of these is the chloroform method, due to VIAL- 

 LANES (Rech. sur I'Hist. et le Dev. des Insectes, 1883, p. 129). I 

 recommend this method for small objects, because I find it 

 more certain and more rapid than the alcohol method and 

 preferable 011 account of a superior consistency it gives to the 

 mass. (ScHiEFFEKDECKER does not find this, v. Zeit.f. wiss. Mik., 



11 



