CHAPTER XXV. 



CORROSION, DEUALC IF! CATION, DBSILICIKICATION, AND 



BLEACHING. 



Corrosion. 



554. Caustic Potash, Caustic Soda, Nitric Acid. Boiling, or 

 long soaking in a strong solution of either of these, is an 

 efficient means of removing soft parts from skeletal structures 

 (appendages of Arthropods, spicula of sponges, etc.). 



555. Eau de Javelle (Hypochlorite of Potash) (NOLL'S Method, 

 Ziiol.Anzeig., 122, 1882, p. 528). The usual method of pre- 

 paring the skeleton of siliceous sponges and similar structures 

 by corroding away the soft parts by means of caustic potash 

 has many disadvantages, of which a principal one is that the 

 spicula are not preserved in their normal positions. NOLL 

 proceeds as follows : A piece of sponge is brought on to a 

 slide and treated with a few drops of eau de Javelle, in which 

 it remains until all soft parts are dissolved. (With thin 

 pieces this happens in twenty to thirty minutes.) The pre- 

 paration is then cautiously treated with acetic acid, which 

 removes all precipitates that may have formed, and treated 

 with successive alcohols and oil of cloves, and finally mounted 

 in balsam. 



The same process is stated to be applicable to calcareous 

 structures. I feel convinced, however, that if the structures 

 are delicate, they will suffer, or be entirely destroyed. 



556. Eau.de Labarraque (Hypochlorite of Soda) may be used 

 in the same way as eau de Javelle. Looss (Zool. Anz., 1885, 

 p. 333) finds that either of these solutions will completely 

 dissolve chitin in a short time with the aid of heat. For this 



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