HARDWICKE'S SCIENCE-GOSSIP. 



145 





ON CLEANING DIATOMACE£, 



By FRED. KITTON, F.R.M.S. 



N spite of the instruc- 

 tions for the above pur- 

 pose which have ap- 

 peared from time to 

 time in this and similar 

 works, I am constantly 

 asked to describe my 

 modus operandi. I do 

 not claim any originality 

 or special merit for the 

 following methods, and 

 I can only say I generally succeed in making good 

 preparations ; and it is probable that those who are 

 accustomed to prepare slides of Diatomacex will learn 

 nothing from these directions, or may have better 

 methods of their own. I am writing for those who 

 have just taken up the study of these organisms, and 

 are anxious to prepare their own slides. Below is a 

 list of apparatus and chemicals required, which, it 

 will be seen, is neither numerous nor costly. 



ArPARATUS. 



A spirit-lamp (or, where gas can be obtained, a 

 Bunsen burner). 



Test-tubes of various sizes and diameters. (It is 

 better to use a small tube if the material to be operated 

 upon is minute in quantity. ) 



Two pint precipitating glasses, with lips. 



Three porcelain saucers, holding one, two, and 

 three ounces. 



Florence flasks are extremely useful when operating 

 on large quantities of material (from one-half to two 

 ounces. 



Litmus-paper. 



CHEMICALS. 

 Hydrochloric acid. 

 Nitric acid. 

 Sulphuric acid. 

 Caustic potash, or soda. 

 No, 151. 



CHEMICALS — contimied. 



Bicarbonate of soda. 

 Liquor ammonire (strongest). 

 Chlorate of potash. 

 Methylated spirit of wine. 

 Pure spirit. 

 Distilled water. 



Diatomaceous material may be divided into three 

 classes, each of ^^•hich will require a different mode 

 of treatment. The first kind, and that which offers 

 the least difficulty to the preparer, are the "pure 

 gatherings,"— that is, those free from extraneous 

 matter. If the forms in it are to be mounted with 

 the valves and frustules not separated, it should be 

 gently heated, so as to kill the diatoms and cause 

 them to subside ; when this has taken place, pour 

 off the water and replace it with methylated spirit, in 

 which they can be kept till wanted : this will dissolve 

 out the endochrome, or colouring matter, and not 

 separate the valves. When the frustules are very stout 

 and not easily broken up, a solution of hydrochloric 

 acid may be used (about five parts of water to one 

 of acid) : this will, in the course of a week, destroy 

 the endochrome. If the diatoms are stipitate or para- 

 sitic on other algre, and it is desirable to mount them 

 in situ, the water in which they are growing must be 

 poured off and replaced by spirit, every trace of which 

 must be washed away before mounting. The slide 

 (or cover, if the specimen is mounted upon it) should 

 now be made sufficiently hot to slightly char the 

 stipes. When the valvular aspect only is required, 

 the gathering must be boiled' in nitric acid for about 

 ten minutes, and after the diatoms have subsided 

 (four or five hours are usually sufficient), the super- 

 natant acid should be poured off and the test-tube 

 about one-third filled with distilled water, repeating 

 the process until every trace of acid is eliminated. 

 (I must caution the operator against allowing the 

 fumes of the acid to come in contact with the stock 



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