APPENDIX. 



1051. Chemicals, Stains, and Apparatus. Addresses of British 

 firms from which it is recommended that these be obtained are 

 given in 11. 



1052. Cleaning Slides and Covers. New ones should first be 

 soaked in one of the following liquids : strong sulphuric, hydro- 

 chloric or nitric acid, or aqua regia, or a mixture of an ounce each of 

 sulphuric acid and bichromate of potash with from 8 to 12 ounces of 

 water, then washed first with water and lastly with alcohol, and 

 dried with a clean cloth. 



For used ones, if a balsam mount, warm, push the cover into a 

 vessel with xylol or other solvent of the mount, and put the slide 

 into another vessel with the same, leave for a few days, and then 

 put into strong alcohol. If this is not sufficient, treat as for new 

 ones. Some persons boil in lysol, which I do not find efficacious. 



For the final treatment, see p. 121. 



1053. Gum for Labels. Labels stuck on glass often strip off. 

 This may be avoided (MARPMANN, Zeit. Angew. Mik., ii, 1896, 

 p. 151 ; Journ. Roy. Mic. Soc., 1897, p. 84) by means of the following 

 adhesive : 120 grms. of gum arabic are dissolved in a quarter of a 

 litre of water, and 30 grms. of gum tragacanth in a similar quantity. 

 After a few hours the tragacanth solution is shaken until it froths, 

 and mixed with the gum arabic solution. Strain through linen and 

 add 150 grms. of glycerin previously mixed with 2J grms. of oil of 

 thyme. 



PEIRCE (Journ. app. Mic., ii, 1899, p. 627 ; Journ. Roy. Mic. Soc., 

 1900, p. 404) finds that if the end of the slide be painted with a thin 

 solution of balsam, it may be written on with ink when dry, and the 

 record preserved by a second coat painted over it. 



For other receipts see early editions. 



362 



