3$2 PALEONTOLOGY 



thoroughly washed and scrubbed, and it is well to preserve 

 the washings and evaporate them to a more concentrated 

 solution of potash, to be used for another purpose 

 mentioned below. 



Many fossils, though stable enough in their long 

 home, are physically or chemically unstable as soon as 

 extracted, and need special treatment to save them from 

 disintegration or the risk of it. If they are simply fragile 

 they must be impregnated with some binding material. 

 The most usual one is gelatine, applied as a hot, strong 

 solution with a soft brush : it penetrates the shell and as 

 it hardens it binds the parts together and prevents decay. 

 It has the disadvantage of requiring very rapid treatment 

 lest it harden before penetrating. Another material 

 is a solution of collodion in amyl acetate : this has the 

 advantage that it hardens much more slowly by evapora- 

 tion. It can be brushed over the shell at intervals of a 

 day or more until no more is absorbed, or small specimens 

 can be dropped into the solution and left there indefinitely. 

 Care must be taken not to inhale the amyl acetate. 



The chief case of chemical disintegration is that of 

 fossils or casts in marcasite. This is an unstable sulphide 

 of iron which absorbs moisture and oxygen, and gives a 

 crystalline efflorescence of ferrous sulphate. As soon as 

 such an efflorescence is noticed, it must be brushed away 

 and the fossil soaked in hot, but not boiling, potash 

 solution to neutralize any free sulphuric acid. It is then 

 washed thoroughly in distilled water to remove the potash, 

 and thoroughly dried on a hot plate, after which it ^s 

 painted all over with shellac varnish (or if not too large 

 soaked in the varnish). In this way further access of 

 oxygen and moisture is prevented. 



When a fossil is represented only by a cavity in a rock, 

 it becomes necessary to take a cast of it. For this 

 purpose many substances may be used paraffin wax, 



