M 30-M 31.1 MOUNTING MEDIA G39 



M 30 Mountants Not Miscible with either Alcohol or Water 



The great majority of all mounts are prepared in these media of which Canada balsam 

 (mixtures containing which form the first class, M 31), is the best known. Gum damar 

 (M 32) is a substance which is so variable in composition that it is difficult to recom- 

 mend it. It has less tendency to become either yellow or acid with age than has balsam, 

 provided that one secures a good specimen. But there are numerous accounts in the 

 hterature of mounts which have become granular within a few years of having been 

 made. It would appear probable that these mounts were made from an impure sample 

 of the gum, and the worker who wishes to use damar media is recommended to be very 

 particular as to his source of supply. The next class (M 33) covers the few otlier natural 

 resins which have from time to time been proposed for mounting media as well as mix- 

 tures of these resins with Canada balsam and with gum damar. The last class (M 34 

 below) is Hkely to increase very rapidly with time. It includes numerous synthetic resins 

 which have been proposed as a substitute for the natural resins usually employed. No 

 methcrylate mixtures are included since there is abundant evidence in the literature 

 (Richards and Smith 1938: 19938, 87:374) that they are worthless. Unfortunately, 

 many authors have proposed media based on resins of which only a trade name is 

 quoted. These have not been included since they are almost impossible to duplicate. 

 Formulas using trade names have, however, been included if a reasonable chemical 

 identification of the resin is given in the original description. 



31 CANADA BALSAM MEDIA 



Canada balsam is the natural exudate of Abies balsamea. It consists of a resin {Canada 

 resin in the formulas given below) dissolved in a variety of hydrocarbons. The material 

 sold on the market as dried balsam has had the lower boiUng-point natural hydrocarbons 

 driven off with heat but the higher boiling-point fractions, which act as natural plasti- 

 cizers, remain. This dried balsam is commonly used as a 40% solution in xylene or ben- 

 zene. If true Canada resin is used, a plasticizer must be added. A method of purifying 

 Canada balsam is given by Bensley and Bensley 1938, 38. Neutral balsams are a delusion 

 and some M 34 formula should be used in their place. 



31.1 Formulas 



31.1 Apathy 1909 8338,22:18 



formula: Canada balsain 50, cedarwood oil 25, chloroform 25 



31.1 Becher and DemoU 1913 Becher and DemoU 1913, 107 



formula: Canada resin 40, abs. ale. 40, terpineol 20 



31.1 Curtis 1905 salicylic balsam — co^npl. script. 1863, 17 :603 



formula: dried Canada balsam 30, sat. sol. salicylic acid in xylene, 70 



31.1 Hays 1865 21400a, 1:16 



formula: Canada balsam 50, chloroform 50 



preparation: Mix ingredients and allow to stand 1 month. Decant. Evaporate to 

 required consistency. 



31.1 Sahli 1885 23632,2:5 



note: This paper is often quoted as recommending a solution of balsam in cedar oil. 

 Sahli recommends only that sufficient of the oil used for clearing be left to soften the 

 balsam. 



31.1 Semmens 1938 CS15a—auct. Microscope, 2 'AQQ 



formula: Dried Canada balsam 40, xylene 20, DS 12.16 McLean 1934b 20 

 note: The substitution [of DS 12.16 McLean 1934a (eosin) gives CS15b and McLean 

 1934a (erythrosin) gives CS15c. 



