226 CLEARING AGENTS. 



not too expensive substance that should combine the properties 

 of clearing quickly alcohol preparations, not dissolving out 

 anilin colours, clearing celloidin without dissolving it, not 

 evaporating too quickly, and not having a too disagreeable 

 smell. 



The following is a list of twenty-four products examined 

 by them. It seems worth while to give it, although the 

 authors only found three amongst the number that fulfil the 

 conditions ; as to know that they have been found wanting in 

 some of these respects may perhaps save somebody a wild- 

 goose chase. 



Oils of Anise, Amber, Birch tar, Cajeput, Calmus, Cassia, 

 Cedar-wood, Citrons, Dill, Field thyme, Fir needles, Mint, 

 Cumin, Niobe, Origanum, Palmarosa, Peppermint, Penny- 

 royal, Rosemary, Sassafras, Spikenard, Thuja, Sandal-wood, 

 Caraway. 



Of these, the following three fulfil the conditions and can 

 be recommended : Cedar-wood, Origanum, Sandal-wood. 



It would be important to possess a list of the exact indices of refraction of 

 the substances used for clearing. I have, unfortunately, not been able to 

 obtain sufficient information of a trustworthy nature for the compilation of 

 such a list. Cedar oil has nearly the index of crown glass (this is true of tire 

 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 the same 

 extent as Canada balsam. Clove oil has a much higher index, and therefore 

 clears more than balsam. Turpentine, bergamot oil, and kreasote have much 

 lower indices, and therefore clear less. 



344. Cedar Oil (NEBLSEN and SCHIEFFEEDECKEB, 1. c., last sec- 

 tion) . For finest cedar-wood oil, price per kilo varies from 

 fifteen to twenty shillings, say about sevenpence halfpenny per 

 ounce for small quantities, or about the price of clove oil. Very 

 thin, colour light yellow, odour slight (of cedar-wood), evapo- 

 rates slowly, is not changed by light, is miscible with chloro- 

 form balsam, and with castor oil. Clears readily tissues in 

 95 per cent, alcohol, without shrinkage, does not extract 

 anilin colours. Celloidin sections are cleared in five to six 

 hours. 



Cheap, but requires an inconvenient length of time for the 

 clearing of celloidin sections. 



The observer should be careful as to the quality of the 

 cedar oil he obtains. I have examined the clearing properties 

 of a sample obtained from the celebrated firm of Rousseau, 



