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X. — Acetone as a Solvent for Mounting Media. 

 By John Kitchie, Jun. 



{Read February 20, 1918.) 



Acetone has during the last few years been used as a reagent for 

 the extraction of water from specimens about to be embedded in 

 paraffin wax, owing to the property it possesses in being able to 

 absorb water from formalin and alcohol, etc. 



Hitherto I have found no record of its use as a solvent for 

 Canada Balsam (or other gums, such as Copal, Dammar and 

 Sandarac), but as I have been successful in obtaining good mounts 

 in such a medium, a few notes as to the methods employed may be 

 of interest. 



Various FormuLv of Medium : — Place in a well-stoppered 

 bottle {a) some Canada balsam in the resinous condition (select the 

 lighter-coloured lumps), over this pour some acetone (commercial). 

 At first the acetone acting on the balsam causes a precipitate of a 

 white flaky character, but in a few hours the medium clears and is 

 ready for use. This formula gives a slightly acid reaction to litmus, 

 to avoid which (h) re-distilled acetone, free from acid, may be used ; 

 but I find that if the mounting process is carried out in an atmo- 

 sphere impregnated with moisture, much care has to be taken to 

 prevent the finished mount taking up and retaining moisture under 

 the cover-glass. Under ordinary atmospheric conditions, however, 

 it gives almost the same results as the (a) formula, (c) Another 

 method is to add 2 or 3 drops of Bouin's Fluid (picric acid 60 c.cm.. 

 40% formalin 18 c.cm., glacial acetic acid 2 c.cm.) to each ounce of 

 acetone before pouring on the resin. This last medium is the most 

 suitable for specimens which are not stained, {d) Other gums such 

 as those previously mentioned may be employed and give almost 

 similar results ; but of course each gives a different refractive 

 index. A recent slide mounted in the acetone- balsam shows a 

 rather lower refractive index than does a slide mounted in xylol or 

 benzole-balsam. 



Two methods may be employed. A. In dealing with large 

 specimens, take the object, either stained or unstained, from any of 

 the grades of alcohol from 70% upwards and place in a bath of 

 acetone, from this transfer the specimen to a glass slip, drop on it 

 any of the above media, and adjust a cover-glass. Specimens which 

 are rather too large to be mounted on slips can be put into small 



