BLEA CHING AND OXIDISING A GENTS. 3 1 5 



The first two are principally used for bleaching vegetable 

 sections, and the strength of the solution may be found in 

 the Receipts at the end of the book. It is most important, 

 when using these reagents, to eliminate every trace of them 

 after the operation is finished, and this may be done by 

 soaking in a bath of neutral sulphite of soda, 15 grains to 

 the ounce of water ; a solution of one part of strong liquid 

 ammonia to twenty parts of water will also effect this. 



Chlorate of potash is generally used for cleaning diatoms, 

 in connection with some strong acid such as sulphuric, nitric, 

 or hydrochloric. Great care should be used in making these 

 mixtures, as it is easy with them to produce explosions, 

 and their use should (in connection with chlorate of potash) 

 be avoided as much as possible. Nitric acid by itself is a 

 powerful bleacher and oxidiser, but has the disadvantage of 

 emitting powerfully noxious and acid fumes ; when slightly 

 diluted to prevent this, its oxidising powers can be increased 

 by the addition of chromic acid or bichromate of potash. 

 This admixture is not in the least likely to explode. 



Another extremely powerful oxidiser is a mixture of 

 strong sulphuric acid and chromic acid in crystals ; it is 

 especially useful in cleansing diatoms, and must be heated 

 carefully over the spirit-lamp to obtain its maximum effect. 

 Peroxide of hydrogen is an extremely valuable bleaching 

 agent and oxidiser, and likely to come into general use 

 when its properties are better known to microscopists ; it is 

 neither acid nor alkaline, and does not give off any objec- 

 tionable odour. Another bleaching agent is turpentine, 

 almost exclusively used to reduce the intensity of colour in 

 the chitinous skeletons of insects. After having been treated 

 with potash or soda solution, and the abdominal contents 

 expressed, the insect is washed with water, dried in alcohol, 

 and allowed to soak in turpentine until the colour of the 

 chitin is sufficiently reduced in intensity. Turpentine has 



