1883.] 



MICROSCOPICAL JOURNAL. 



193 



\ 



While making these experiments 1 

 essayed various media for making 

 solutions out of which the substance 

 should crystallize. Distilled water 

 gave indiiTerent results ; as also, 

 water holding gum arable in solution. 

 Sulphuric aether was excellent, and 

 absolute alcohol still better ; but what 

 made success assured, was the employ- 

 ment of glacial acetic acid added to 

 absolute alcohol, in the proportion of 

 from five to twenty per cent. To this 

 mixture was added the ethyl-aether of 

 gallic acid, in the proportion of from 

 live to twenty per cent., dissolved in a 

 small test-tube, preferably without 

 heat, and distributed upon glass slips, 

 as follows : Let a thin slide be held 

 with the left forefinger and thumb, 

 and on its left end let there be poured 

 a quantity of the solution, quickly made 

 to run over the rest of the glass, and 

 to drain at once into the reservoir 

 tube. Then let it be laid flat, and 

 protected against dust, for evapora- 

 tion. The operator should prepare 

 many such slides — make some lie flat 

 and others inclined — and when per- 

 fectly dry, should pass the slides be- 

 tween the Nicols, using an inch 

 objective, and mark the best spots 

 •with ink on the back. 



After some hours the chosen crystal 

 film is mounted, by touching the cen- 

 tre with a small drop of the rosin and 

 copaiba, placing upon it a cover-glass, 

 pressing this rather firmly down, and 

 allowing capillary attraction with time 

 to complete the even spread. 



At leisure a diamond cuts out the 

 mounted parts, and tragacanth at- 

 taches them upon wooden slips with 

 a f inch aperture ; when, after label- 

 ing, the preparations will be complete. 

 And the bits may be further secured 

 by running a solution of shellac along 

 the edges. 



I much prefer this mode of pre- 

 paring such objects for the polariscope, 

 for the chances of the best fields are 

 greatly increased, as well by the ex- 

 tent of surface as by the varying quan- 

 tity of its solution, at the ends, sides 

 and middle. And be assured that 



the centre of the slide will be the 

 last place to look for the most suc- 

 cessful grouping. 



Finally, dust the surfaces of the 

 cover-glasses protecting these prepa- 

 rations gently with a camel's-hair peu- 

 cii ; but on no account wipe them until 

 some months shall have elapsed. 



The figures presented are chiefly 

 discs and rosettes, in all varieties of 

 grouping and size ; some thin, grey 

 or bluish, others larger or smaller, of 

 the most intense hues ; some coal- 

 esced and others discreet ; some del- 

 icately fringed, while very rarely in- 

 deed the most beautiful disc occurs, 

 of moderately large size — microscop- 

 ically speaking — with corrugated ra- 

 diations proceeding from a central 

 sharp-cut cross, surrounded with a 

 ring of color before it sends out its 

 brushes, and ending in a ruffled mar- 

 gin of several rows deep. The ele- 

 gance of the preparation and the cer- 

 tainty of its preservation, even in the 

 copaiba and rosin fluid depend, as I 

 have found, upon the circumstances 

 attending the crystallization ; one of 

 these attaches to the perfect drying 

 of the film and the dissipation of the 

 acetic acid; and the other refers to 

 the solvents employed. The best of 

 these, in my experience, for the ethyl- 

 ajther of gallic acid, are absolute alco- 

 hol acidulated with the glacial acetic 

 acid ; and the other, even better, per- 

 haps, an equal mixture of absolute 

 alcohol and sulphuric aether acidu- 

 lated from five to ten per cent, with 

 the same acid. And, if these condi- 

 tions be attended to, there need be no 

 doubt as to the result. 



I would add, in conclusion, that 

 ethyl-aether of gallic acid, salicylate 

 of cinchonidia, cholesterine, ' and 

 some other substances, being very 

 soluble in Canada Balsam, I have 

 treated them by placing a small quan- 

 tity of either upon a drop of recent 

 balsam, melting by heat, and placing 

 and pressing down firmly a warm 

 cover upon the saturated fluid. And 

 the drop may be stirred or not stirred. 

 In time most charming crystallizations 



