264 THE AMERICAN MONTHLY [Sept., 



purpose it is essential that its refractive index should coincide 

 as nearly as possible with that of the lenses with which it comes 

 in contact, and it is usually neccessary to condense the oil to 

 fome extent. Schimmel's ordinary cedar-wood oil is stated to 

 have a refractive index N.D. 1.505(57 at 17° which becomes N.I). 

 1.51682 when the oil is condensed. — PharmaceutlcalJournal. 



Mailer's fluid. — Equal parts bichromate of potassium and 

 of suli)hate of sodium dissolved in water, say 2 grammes of 

 each salt to 1,000 cc. water, make the best preservative for speci- 

 mens. It should be changed daily at first and biweekly after. 



MICROSCOPICAL MANIPULATION. 



Cleaning Microscopic Slide and Cover Glasses. — In- 

 stead of warming the slides one by one over a flame, pushing off 

 the covers, then scraping away the balsam and cleaning with al- 

 cohol, put all your slides together in a saucepan with a lump of 

 washing soda and boil them. The heat of boiling is enough to 

 soften most cements and all ordinary resins used for mounting, 

 and then take out the slides one by one, push off the cover- 

 glasses, and put them back. The action of the soda is to con- 

 vert the balsam or other resin into a grumous mass, which is 

 easily wii)ed off with a little rinsing. Cover-glasses can also be 

 preserved for further use in the same way, if desired. There 

 being nothing on the surface of new covers and slides which 

 will resist the action ofhot water and soda, this method is prefer- 

 able to the use of strong sulphuric acid, alcohol or the other meth- 

 ods given in the text-books. The exact quantity of soda to be used 

 is immaterial; a piece about the size of an egg to half a pint of 

 water will do. 



Solution of Bleached Shellac. — Most of the journals ^vhich 

 give directions for dissolving bleached shellac say " soften the 

 shellac by soaking in ether until the gum is swollen, pour off the 

 ether, and add alcohol." The person who tries this will find 

 himself at the end with a large proportion of undissolved shellac. 

 If, however, he takes the precaution to allow the softened shel- 

 lac to stand awhile, after pouring off the ether, until all of the 

 later not taken up by the shellac has evaporated, and then to 

 use absolute alcohol as a solvent, there will be but little undis- 

 solved shellac. 



