EXAMINATION AND PRESERVATION MEDIA. 



235 



the optical effects of various media. The figures give the 

 approximate indices of refraction. They should be accepted 

 with some caution, on account of the variability of samples. 

 The figures given for balsam refer evidently to the resin in the 

 solid state and not to the solutions used for mounting, which 

 are certainly much lower, according to the lower index of 

 the solvent. 



Ail- 

 Methyl alcohol . 

 Distilled water . 

 Sea water .... 

 Solution of white of egg 

 Absolute alcohol 

 Acetate of potash, saturated 



aqueous sol. 

 Glycerine with an equal 



quantity of water . 

 Chloride of calcium, 90 per 



cent, in water . 

 Glycerine, Price's 

 Oil of hergamot . 

 Paraffiiiuni liquidum . 

 Olive oil . 

 Oil of turpentine 

 Glycerine, " concentrated " 

 Gilson's Baume an Camsal 

 Gilson's Euparel 

 Terpinol . 

 Castor oil 



1-000 

 1-323 

 1-336 

 1-343 

 1-350 

 1-367 



1-370 

 1-397 



1-411 

 1-460 

 1-464 

 1-471 

 1-473 

 1-473 

 1-473 

 1-478 

 1-483 

 1-484 

 1-490 



Xylol . . . 1-497 

 Cedar- wood oil, not thick- 

 ened .... 1-510 

 Crown glass . . . 1*518 

 Cedar-wood oil, thickened . 1*520 

 Gum damar . . . 1'520 

 Xylol balsam . . . 1'524 

 Oil of lemons . . . 1*527 

 Oil of cloves . . . 1'533 

 Canada balsam (solid) . 1*535 

 Creasote .... 1*538 

 Coloplionium . . . 1*545 

 Carbolic acid . . . 1*549 

 Oil of anise seed. . . 1*557 

 Oil of cinnamon (or cassia) 1'567 

 Anilin oil . . . . 1-580 

 Sulphide of carbon . . 1*630 

 Tolu balsam . . . 1'640 

 Monobromicle of naplitlia- 



lin 1*660 



Solution of sulphur in sul- 

 phide of carbon . . 1'750 



It will be seen that cedar oil has nearly the index of 

 crown glass (this is true of the oil in the thick state to which 

 it is brought by exposure to the air not of the new, thin 

 oil, which is less highly refractive) ; it therefore clears to 

 about the same extent as Canada balsam. Clove oil has a 

 much higher index, and therefore clears more than balsam ; 

 cinnamon oil higher still. Turpentine and bergamot oil have 

 much lower indices, and therefore clear less. 



Watery Media. 



401. Isotonic and " Indifferent" Liquids. The old distinction 

 of "Indifferent' liquids, and those which have some action 

 on tissues, appears to be misleading more than helpful ; for 



