APPENDIX. 



927. Chemicals, Stains, and Apparatus. — Addresses from which 

 it is recommended that these be obtained are given in § 11. 



928. Cleaning Slides and Covers. — New ones should first be 

 soaked in one of the following liquids : strong sulphuric, 

 hydrochloric or nitric acid, or aqna 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. 



929. 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. 8oc., 1897, p. 84) by means of the 

 following adhesive ; 120 grammes of gum arabic are dissolved 

 in a quarter of a litre of water, and 30 grammes of gum tra- 

 gacanth in a similar quantity. After a few hours the tra- 

 gacanth solution is shaken until it froths, and mixed with 

 the gum arabic solution. Strain through linen and add 150 

 grammes of glycerin previously mixed with 2^ grammes of 

 oil of thyme. 



Peiecb {Journ. app. Mic, ii, 1899, p. 627; Journ. Boy. Mic. 

 Soc, 1900, p. 404) finds that if the end of the slide be 

 painted with a tliin 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. 



