470 APPENDIX. 



are scraped free of the mounting medium with a knife and put directly into 

 the bichromate solution. 



FOL (Lehrb., p. 132) recommends either a solution containing 3 parts of 

 bichromate, 3 of sulphuric acid, and 40 of water ; or simply dilute nitric 

 acid. 



GABBINI (Manuale, p. 31) puts slides for a day into 10 per cent, sulphuric 

 acid, then washes, first with water and then with alcohol. 



BEHEENS (Zeit. f. wiss. Mik., 1885, p. 55) treats slides first with con- 

 centrated nitric acid, then with water, alcohol, and ether. 



JAMES (Journ. Roy. Mic. Soc., 1886, p. 548) treats used slides with a 

 mixture of equal parts of benzin, spirit of turpentine, and alcohol. 



KNAUEB (Centralbl f. Bakt., x, 1891, p. 8 ; Zeit. f. wiss. Mik., ix, 2, 

 1892, p. 187 ; Journ. Roy. Mic. Soc., 1891, p. 833) recommends boiling for 

 twenty or thirty minutes in 10 per cent, lysol solution, then rinsing with 

 cold tap water till clear. 



NIAS (Journ., pag. cit.) finds it is sufficient to boil with washing soda, and 

 rinse. 



865. G-um Mucilage for Labels, &c. The Journ. of the Chemical 

 Soc. says that the adhesive qualities of gum may be very much exalted by 

 the addition of aluminium sulphate (the so-called " patent " alum) to the 

 mucilage. " 2 grms. of crystallised aluminium sulphate, dissolved in 20 

 grms. of water, is added to 250 grms. strong gum arabic solution (2 grms. 

 in 5 grms. water). Ordinary solutions of gum arabic, however concen- 

 trated, fail in their adhesive power in many cases, such as the joining 

 together of wood, glass, or porcelain ; prepared, however, according to the 

 above receipt, the solution meets all requirements " (from Public Opinion, 

 Feb. 19th, 1886). 



FOL (Lehrb., p. 148) advises that slides be prepared for labelling by 

 spreading over one end a layer of aluminium-chloride gelatin dissolved in 

 acetic acid, and allowing it to dry before putting on the label. 



Why do not the glass makers furnish slides with roughened (ground) end- 

 surfaces for the reception of labels ? 



For four other receipts for gums and pastes for labels, see ELIEL, in 

 Engl. Mechan., 1887, p. 535 ; Amer. Mon. Mic. Journ., 1887, p. 93 ; Zeit. 

 f. wiss. Mik., v, 1, 1888, p. 69. 



VOSSELEB (Zeit. /. wiss. Mik., vii, 4, 1891, p. 459) recommends, for 

 attaching protective cardboard ridges to slides, a syrup-thick solution of 

 bleached shellac in alcohol. 



866. Green Light. The suggestion of the employment of green light 

 in microscopy is, I believe, due to ENQLEMANN (Pfliiger's Arch., 1880, p. 

 550). He strongly recommends the use of green light for delicate observa- 

 tions, as giving sharper definition, allowing finer detail to be seen, and tiring 

 the eyes less than white light. Green glass of sufficiently good quality is 

 found in commerce. The glass is best put between the mirror and the object, 

 e. g. on the diaphragm. Blue glass (cobalt or amrnon i *o-sulphate of copper) 

 is also useful, but less so than green. Red light is most hurtful. " The 

 explanation of these points, so important in practice, may be found in the 

 results obtained by Lamansky in his researches on the * Limits of Sensi- 



