Xyloc

XYLOC (Xylol) C₆H₄(CH₃)₂], dimethylbenzene, exists in three isomers: ortho [boiling point 144.4°, specific gravity 0.880 at 20°/4°], meta [boiling point 139°, specific gravity 0.864 (20°/4°)], and para [boiling point 138°, specific gravity 0.861 (20°/4°)]. Commercial xyloc is an unstable mixture of these isomers. In microscopy, K. is used as an intermediate medium when embedding in paraffin or mounting in Canadian balsam because it dissolves them very well. It does not dissolve collodion. With water, K. forms an emulsion. It mixes with alcohol in any proportions, but when the latter contains more than 4% water, it causes cloudiness. Because of this, K. can serve as a reagent to determine water content in alcohol (in the absence of precise alcoholometers). K. extracts certain dyes from stained preparations, for example, acid fuchsin and especially picric acid. With prolonged action, it destroys the products of reduction of silver nitrate and osmic acid. To reduce the sensitivity of xyloc to water content in alcohol, carbolic acid or acetone is added to the latter, which makes it possible to transfer collodion sections directly from 90-94% alcohol to K. When acetone is added, three mixtures are prepared, through which objects are passed directly from water to K., bypassing alcohol (water→acetone→3 parts acetone+1 part K.→1 part acetone+1 part K.→1 part acetone+3 parts K.→K.). This method allows preparations stained with azure-eosin (Giemsa) to be mounted in Canadian balsam without exposing them to the risk of being washed out by alcohol. K. easily penetrates tissues and, displacing alcohol from them, clears them, but with prolonged action, connective tissue becomes brittle. The speed of clearing small objects is about 30-60 minutes.