VIO 



VARIOUS FORMULAS 



651 



may encourage mounters to revert to 

 fluid mounts. The next section (on ad- 

 hesives — V 20) is self-explanatory, though 

 few people today seem to think it neces- 

 sary^ to cause to adhere to a slide any ob- 

 ject except a paraffin ribl)on, or, even in 

 that case, to realize that materials other 

 than egg albumen may be used with ad- 

 vantage. The next section (on media for 

 injection — V 30) contains many formulas 



which cannot be ignored by any preparer 

 of microscope slides whether for teaching 

 or research purposes. The two last sections 

 (on cleaning methods and formulas — V 40, 

 and miscellaneous formulas — V 50) are of 

 little importance but provide a final rest- 

 ing-place for formulas which the writer 

 considers worth publishing but which can- 

 not be placed elsewhere. 



V 10 Cements, Lutes, and Varnishes 



These materials are used for two pur- 

 poses. The first is the attachment of 

 objects, either supporting structures such 

 as cells (see Chapters 1-3) or objects for 

 examination, to sHdes; or second, they 

 are used to seal edges of covershps in 

 order to retain under the cover some 

 mounting medium. The formulas are here 

 divided into those which are in fluid form 

 and those which must be melted before 

 application. It must be remembered, how- 

 ever, that the majority of the soHd 

 cements may be dissolved in a suitable 

 solvent and used as though they were 

 fluid. If this is done, it is well to heat the 

 dried cement to get rid of the last trace 

 of solvent. 



Care must be taken, in following old 

 directions as to the sealing of micro- 

 scopical preparations, that one uses actu- 

 alh^ the material intended by the writer 

 and not that which at the present time 

 passes under the same name. Thus the 

 modern marine glue bears no relation at 

 all to the solution of shellac in gutta 

 percha which was the marine glue used by 

 the early microtomists. The formula given 

 below (V 12.2 Harting 1880) is very close 

 to the original marine glue, but there is 

 no means of finding out whether or not it 

 is identical with the material ("G 4") 

 specified by the early writers and blindly 

 copied by many later ones. Another 

 source of constant confusion is gold size. 

 This was originally partially polymerized 

 and oxidized linseed oil diluted with 

 turpentine, and was specified for the use 

 of gilders because it remained tacky for a 

 long time, thus enabhng the leaf gold to 

 be applied to a complex ornament over a 

 long period. Modern varnishes having the 

 same property of remaining tacky are 



available on the market under the name of 

 gold size, but are entirely unsuitable for the 

 preparation of microscope slides. Another 

 misunderstood term is sealing wax. In the 

 earlier days sealing wax contained con- 

 siderable quantities of Venice turpentine 

 and of beeswax, as well as the shellac of 

 which it is now almost completely com- 

 posed. In the following pages will be 

 found formulas giving so far as is possible 

 the original ingredients. 



Shellac itself is a term capable of mis- 

 interpretation. Orange shellac is a natural 

 exudate, caused by insect damage, from 

 the bark of many resinous trees. It is a 

 mixture of alcohol-soluble resins and 

 naphtha-soluble waxes. White shellac is 

 produced by the action of chlorine on alka- 

 line-aqueous solutions (in part "soaps") 

 of orange shellac. The alcohol-soluble 

 fraction of this chlorinated shellac poly- 

 merizes very rapidly, at temperatures just 

 below its melting point, into a material 

 which is insoluble in alcohol or any other 

 common solvent. Hence a "cell" turned 

 from V 11.2 Gage 1901 (below) can 

 be used for an alcohol mount if the 

 dewaxed shellac called for in the formula 

 is prepared from white shellac and 

 the ring-baked. BeUido 1927 (11360, 

 47 :27) specifies heat treatment for shellac 

 cells used in the mounting of diatoms in 

 bromonaphthalene. 



The only confusion which is likely to 

 arise among solvents is in the use of the 

 term benzine, a petroleum fraction now- 

 adays sold as hgroin. It has none of the 

 properties of benzene nor should it be con- 

 fused with the low-boihng-point petroleum 

 ether which is sometimes specified in its 

 place. 



