EXAMINATION AND PRESERVATION MKIUA. 



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. 



Air 1-000 



Methyl alcohol . . . 1*323 



Distilled water . . . 1-336 



Sea water .... 1-343 



Solution of white of egg . 1*350 



Absolute alcohol . . T367 

 Acetate of potash, saturated 



aqueous sol. . . . 1*370 

 Glycerine with an equal 



quantity of water . . 1*397 

 Chloride of calcium, 90 per 



cent, in water . . . 1*411 



Glycerine, Price's . . 1'460 



Oil of bergamot . . . 1*464 



Paraffinum liquidum . . 1*471 



Olive oil .... 1-473 



Oil of turpentine . . T473 



Glycerine, " concentrated " T473 



Gilson's Baume an Canisal T478 



Gilson's Euparel . . T483 



Terpinol .... T484 



Castor oil . T490 



Xylol 1-497 



Cedar-wood oil, not thick- 

 ened .... 1-510 

 Crown glass . . . T518 

 Cedar- wood oil, thickened . 1'520 

 Gum damar . . . 1*520 

 Xylol balsam . . . T524 

 Oil of lemons . . . T527 

 Oil of cloves . . . 1*533 

 Canada balsam (solid) . T535 

 Creasote . . . . T538 

 Colophonium . . . T545 

 Carbolic acid . . . 1*549 

 Oil of anise seed. . . T557 

 Oil of cinnamon (or cassia) 1*567 

 Anilinoil .... 1*580 

 Sulphide of carbon . . 1*630 

 Tolu balsam . . .1-640 

 Monobromide of naplitha- 



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 liave some action 

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



