10 BOTANICAL MICROTECHNIQUE. 



solution and in various degrees of concentration. Besides, 

 solutions of potassium hydrate in alcohol or in various mix- 

 tures of alcohol and water are recommended for clearing. 

 For complete clearing several hours are often necessary, 

 sometimes even several days, though it can often be has- 

 tened by warming. After the removal of the solution and 

 superficial washing with water, the free potassium is best 

 neutralized with dilute hydrochloric or acetic acid. If the 

 preparations are then too opaque, they can be again treated 

 with caustic potash or made more transparent with ammonia. 



The well-washed preparations can usually be preserved 

 for a time in glycerine-gelatine ; but after a few years they 

 usually become dark and often cloudy also. 



For staining preparations treated with caustic potash 

 Errera (IV) recommends canarin, which is not decomposed 

 by that reagent. 



2. Phenol (C 6 H & OH). The best for clearing is a solution 

 of crystallized phenol, which contains only water enough to 

 keep it fluid at ordinary temperatures. This penetrates cut 

 parts of plants relatively fast, and usually makes them fully 

 transparent in a short time. The clearing may be markedly 

 hastened by heating the objects in the phenol solution to 

 boiling ; and at the same time the air is completely expelled 

 from the intercellular systems. 



Objects cleared with phenol can, according to my experi- 

 ence, be well preserved in Vosseler's turpentine (cf. 27). 



3. Chloral Hydrate (CC1 3 .CH(OH) 2 ) has heretofore been 

 used commonly for clearing in a concentrated aqueous solu- 

 tion. This can be used as well with fresh as with alcoholic 

 material. To hasten the extraction of chlorophyll one may 

 use successfully a concentrated alcoholic solution of chloral 

 hydrate. The reaction may also be hastened by warming. 



4. Eau de Javelle. A solution of potassium hypochlorite 

 (KC1O) is known in pharmacy as Eau de Javelle (Javelle 

 water). This can at any time be obtained ready for use 

 from an apothecary ; but it may also be prepared by adding 

 to a concentrated aqueous solution of chloride of lime a 

 solution of potassium oxalate, as long as a precipitate is 



