DECOLORIZING DESILICIFICATION 297 



should be used, and the material should be left in this until 

 decalcincation is found to be complete. 



Decolorizing. Material which has become brown in alco- 

 hol may be decolorized in the following solution: To each 100 

 c.c. of alcohol is added from 0.2 to 0.5 c.c. of concentrated 

 sulphuric acid and as much potassium chlorate as can be trans- 

 ferred on the point of a knife. The material is to lie in this 

 solution for eight or ten days, and is then to be transferred to 

 alcohol or to equal parts of alcohol, glycerine and water for 

 preservation. See also under Brown Discoloration and under 

 Clearing. 



Dehydration. This is best accomplished by cutting the 

 material into as small pieces as is practicable, and then placing 

 it in 20 per cent, alcohol, and then into ascending grades of 

 alcohol of 10 per cent, increase at intervals of about two hours. 

 Microtome sections mounted on the slide may be transferred 

 to strong alcohol without injury. In passing from water or 

 aqueous stains to Canada balsam, the material should first 

 come into strong alcohol, and then into xylol to insure complete 

 dehydration, and to infiltrate the material with a solvent of 

 balsam namely, xylol. Aniline is also a good dehydrating 

 agent. The preparations may pass directly from water into the 

 aniline and from the aniline into the balsam. A stick of potas- 

 sium hydrate placed in the aniline will keep the latter dehy- 

 drated. Potassium hydrate is not soluble in aniline. Very 

 thin microtome sections which are found not to be injured by 

 drying may be allowed to dry, and then may be placed in xylene 

 and thereafter transferred to balsam. See page 260 for further 

 description of the process of dehydrating. 



Desilicification. This is accomplished by hydrofluoric acid. 

 A glass vessel is coated on the inside with melted paraffin to 

 prevent the action of the acid on the glass. Alcohol is then 

 poured into the vessel and the material is immersed in the 

 alcohol; then the hydrofluoric acid is added, drop by drop. 

 The process should be completed in a few minutes. Care must 



