1880.] 



MICKOSCOPICAL JOUKNAL. 



109 



sometimes happens that some traces 

 of the cellulose of the diatoms, or 

 of filamentous algae which usually 

 accompany them, even in the clean- 

 est gatherings, are not removed by 

 the boiling, but can afterwards be 

 seen, as clean, white filaments. 

 These bits of cellulose are capable 

 of oxidation, but often resist all but 

 the most powerful oxidizers. In 

 case they are numerous, the best 

 way to destroy them is to pour off 

 the nitric acid from the diatoms, 

 wash them with water, and then 

 use strong sulphuric acid and chlor- 

 ate of potash, in the manner to 

 be described elsewhere in this article. 

 Although nitric acid may not remove 

 the cellulose at once, it is not always 

 necessary to resort to the action 

 of the sulphuric acid process, and 

 usually it is not advisable to do so, 

 for the nitric acid will have con- 

 verted the cellulose into a substance 

 that is chemically analogous to gun- 

 cotton, nitro-cellulose, and this nitro- 

 cellulose will instantly dissappear if 

 the frustules are dried and heated 

 upon a cover-glass. 



Now that we have explained the 

 action of nitric acid, we will de- 

 scribe, in detail, the process which 

 we would recommend for cleaning 

 rather pure gatherings of living or 

 recent diatoms. The operations 

 can be readily conducted in test- 

 tubes about six inches long. 



1. Shake the material in water, 

 if it contains any impurities that 

 can be mechanically separated in 

 that way. If it is a marine or 

 brackish water gathering, wash in 

 fresh- water to remove the salts from 

 the sea-water. Pour off all the water, 

 and if the diatoms are then some- 

 what dried, it will be all the better. 



2. Boil in nitric acid, until oxida- 

 tion appears to be complete. A 

 few minutes boiling will suffice, and 

 the less time the acid is allov/ed to 

 act the better it will be for the more 



delicate or finely marked diatoms. 

 Some persons add a few crystals of 

 chlorate of potash to the boiling 

 acid just before the boiling is fin- 

 ished. This hastens the oxidation 

 somewhat, but very little should be 

 used, enough can be held on the 

 end of a knife-blade. 



3. Fill the tube with filtered 

 water, allow all the diatoms to set- 

 tle, pour off the water, and repeat 

 these operations until the acid is 

 entirely washed out. The residual 

 mass, at the bottom, should be of a 

 pure white color. If it is not, and 

 the operator thinks the nitric acid 

 has acted to its full power, the sul- 

 phuric acid process should be re- 

 sorted to. 



4. It is now necessary to sepa- 

 rate the debris and flocculent matter 

 from the perfect frustules. Among 

 the many methods described in 

 books, we have found the one here 

 described to be applicable to every 

 collection we have cleaned. First 

 add ammonia, th.e aqua ammonia of 

 the druggist, to cover the diatoms 

 to the depth of about one inch, 

 allow to stand about fifteen minutes, 

 then fill the tube with water, allow 

 to settle, and pour off the water 

 once. Then cover the diatoms with 

 water to the depth of about two 

 inches, shake thoroughly, set the 

 tube uprght and allow it to stand, 

 undisturbed, fifteen seconds, then 

 pour the supernatant fluid into a 

 clean test-tube, and repeat the pro- 

 cess in the first tube from three to 

 five times, according to the quan- 

 tity of material that settles through 

 the two inches of water in fifteen 

 seconds, each time pouring off into 

 the second tube, which should be 

 larger than the first one. In the 

 second tube let all the diatoms set- 

 tle, then transfer them to a tube 

 just like the first one, cover with 

 water to the depth of two inches as 

 before, and allow to settle one min- 



