47 



kept melted. This is the temperature for embed- 

 ding. This simple device serves all the purposes 

 of an elaborate paraffin oven (Fig. 8). 



4. Alcohol. — Absolute alcohol in the tropics 

 has absorbed a good deal of water, and it is 

 necessary to dehydrate it. 



Heat crystals of CUSO4 till a white mass is 

 formed. Allow to cool, and place in a tall bottle 

 of alcohol. Allow to settle and decant off alcohol 

 as required. Add fresh anhydrous CuSO^ if a 

 marked blue tint develops, or tie up the anhydrous 

 copper sulphate in a muslin bag, and place in the 

 alcohol pot. 



Gelatine may be used to dehydrate alcohol ; 

 it must previously be washed free from salts by 

 soaking in water. 



5. Xylol. — Xylol is the most generally satis- 

 factory agent for displacing the alcohol and allow- 

 ing the paraffin to permeate the tissue. Chloro- 

 form, wood naphtha, turpentine, oil of cloves, and 

 other substances may be used. 



6. Paraffin. — For use in the tropics, paraffin 

 melting at sixty degrees will scarcely be found too 

 hard. At high altitudes a softer will be required, 

 and the right degree of softness must be deter- 

 mined and produced by mixtures of paraffin melt- 

 ing at 60° C. and paraffin of lower melting point, 

 say 50° C, such as is suitable for use in temperate 

 climates. 



To obtain paraffin suitable for use in a given 

 temperature place a block of paraffin in holder 

 and cut thin sections. 



(fl) If the sections curl very much the paraffin 

 is too hard. 



