86 



THE AMEKICAN MONTHLY 



[May, 



The Gum of Liqiiidamljar Styra- 

 ciflua or American Storax as a 

 Mounting Medium. 



BY PROP. A, B. AUBERT. 



This gum is an exudation of the sweet 

 gum tree of the Southern States, sci- 

 entifically known as Liquidarnbar 

 styracijlua. The more tropical the 

 climate the greater the quantity of 

 gum produced. 



The gum is usually light-colored, 

 being at times nearly white, while 

 other specimens may be considerably 

 darker, of a greyish yellow or light 

 brown color. In consistency it varies 

 somewhat, but is generally as thick as 

 pine pitch of good quality. It is sol- 

 uble in alcohol, ether, chloroform and 

 benzole. Its odor is pleasant. Cin- 

 namic acid and styracin are among its 

 constituents. 



Through the kindness of a friend I 

 have been able to use the gum as a 

 mounting medium, and have been 

 very much pleased with it. I have 

 had to work with rather small quan- 

 tities, but I find a chloroform solu- 

 tion all that can be desired for diatom 

 mounts. A benzole solution replaces 

 most satisfactorily the benzole-balsam 

 solution. 



The method of preparing these solu- 

 tions is simple enough, and anybody 

 who can obtain a specimen of the gum 

 will find it easy to prepare them for 

 use. When the specimen is small it 

 may be exposed in an open vessel in 

 the water-oven to a temperature of 

 ioo° C. for fi-om four to eight hours. 

 This thoroughly dehydrates the gum, 

 and when cool and hardened it may 

 be dissolved in benzole or chloro- 

 form ; this solution must be set aside 

 for a few days to allow flocculent 

 matter to form and settle, then fil- 

 tered, and, if necessary, a part of the 

 solvent evaporated. 



There is a better way of preparing 

 the solutions, but a larger quantity of 

 the gum must be obtained in order to 

 carry it out. The first step in this 

 process is the filtration or straining of 

 the gum. This is done by cutting the 

 bottom out of a small wide-mouthed 



bottle, tying muslin of rather loose 

 texture over the mouth, inverting the 

 bottle over a vessel, and partl}^ filling 

 it with gum ; now expose the whole 

 apparatus to the heat of a water-oven 

 for from six to ten hours. The gum 

 melts and filters through the muslin. 

 The filtered product is of a clear am- 

 ber color, readily dissolves in the sol- 

 vents, and gives much lighter solu- 

 tions than can be obtained by the 

 first-mentioned process. 



The gum is so adhesive that it can- 

 not be gathered without including 

 some debris of bark, wood, etc.; these, 

 when not separated by filtration, give 

 up some coloring matter to the sol- 

 vent, rendering the solution some- 

 what darker. The solution obtained 

 from filtered gum is not much darker 

 than Canada balsam. 



In using these solutions as mount- 

 ing media the method of procedure 

 is very similar to that for balsam 

 mounts. The chloroform solution I 

 have used exclusively for diatoms, 

 boiling a few seconds to expel all air. 

 When mounting in the benzole solu- 

 tion objects are dehydrated in abso- 

 lute alcohol, cleared in oil of cloves,* 

 which must be carefully drained oft' 

 and absorbed by blotting-paper be- 

 fore adding the drop of gum solution 

 and applying glass cover. It is best 

 to harden the mounts in a warm 

 place. When slides are allowed to 

 harden at ordinary temperatures the 

 gum may show "signs of cloudiness ; 

 this is readily made to disappear by 

 the application of a little heat, and I 

 have never observed the turbidity to 

 reappear after this treatment. 



'My experience with the gum has 

 proved that it can in about all cases 

 be used instead of Canada balsam, 

 indeed that it is superior to balsam, 

 showing the finer parts of objects 

 more clearly. I have entirely dis- 

 carded balsam for diatoms. Carti- 

 lage when properly stained shows 

 very well, better in my opinion than 



* I am not entirely satisfied with oil of cloves to clear 

 objects that are to be mounted in this medium. As 

 time permits I hope to experiment on other essential 

 oils. 



