PREPARATION OF DIATOMS. 7 I 



never runs in ; after standing an hour or two I give a finishing ring 

 of same, or the usual black varnish on the outside. I think anyone 

 who will adopt the mode of mounting on the cover, and subsequent 

 heating, as above described, whatever may be the rest of the pro- 

 cedure, will never consent to give up this part, since it effects so 

 even a distribution and such destruction of residual organic matter, 

 and gives such increased brilliancy to the preparations ; sometimes, if 

 the acid has not been thoroughly washed out of acid-treated speci- 

 mens, snappy explosions will occur when the alcoholic mixture is 

 heated ; of course, the remedy is to pour off, and replace with pure 

 water and alcohol." 



Mr. Fred Kittoris method. -The learned English diatomist, Mr. 



Fredk. Kitton, has been good enough to send me a manuscript 



note of the method which he adopts in preparing diatoms. The 



reader will find in it much important information. " When cleaning 



diatoms," says Mr. Kitton, " I prefer to add at the end of the 



operation some small crystals of potassium chlorate, which I find 



easier to use than the aqueous solution of that salt, for if you add 



the latter rather too abruptly it produces such a brisk effervescence 



that the contents of the tube are liable to be projected. When the 



mass has been bleached and all acid got rid of by washings with 



pure water, I drain off the latter and pour 30 to 40 drops of 



concentrated liquid ammonia into the test tube which I stopper with 



a cork. The tubes which I use are 15 centimeters long and two 



centimeters in diameter. I leave the ammonia to react from half-an- 



hour to six hours. I then add 15 grammes of distilled water, and I 



give the tube a good shaking. When the diatoms have fallen to the 



bottom of the tube I draw off the supernatant water, which is often 



very thick, I add a fresh quantity of water and give it another shaking. 



I proceed in this way until every trace of ammonia has disappeared. 



Guanos, marine soundings, and certain fossil deposits require a different 



treatment. 



" When every trace of acid has disappeared, I boil the gathering for 

 three or four minutes in about 30 grammes of water, to which I add a 

 piece of soap the size of a pea. When the diatoms have fallen to 

 the bottom of the flask I remove the soapy water and boil the gathering 

 in pure water. If these methods have been thoroughly carried out the 

 residue will only consist of sand and diatoms. Should the gathering 

 contain any large or heavy forms which I wish to secure for selection 

 I allow the liquid to rest for 20 or 30 seconds, to allow them to 



