24 DIATOMAfT i;. 



slides over the lamp; and such as are sold at house-furnishing 

 stores and by grocers, under the name of American clothes- 

 pegs, and which have been already mentioned, are by far the 

 best I have ever seen or heard of. A small pair of brass for- 

 ceps which close with a spring will be needed, and they are best 

 set iu a wooden handle, so as to protect the fingers from the 

 heat; and another pair, which spring open and may be closed 

 by means of the finger and thumb, will be wanted for taking 

 hold of and adjusting the thin covers. I do not advocate the 

 use of paper covers for slides, but labels of some kind will, of 

 course, be required, and I have found the plain circular white 

 ones to look the best. There are very pretty square labels sold 

 by dealers in these things that I have used and liked. For 

 making cells to hold specimens put up in fluid, a turn-table and 

 brushes and some cement will be necessary. The cement I use 

 and prefer above all others is good old gold size, used warm. 



The chemicals required are nitric acid, sulphuric acid, hydro- 

 chloric acid, bichromate of potash, caustic potash, alcohol, 

 and, above all, a plentiful supply of clean, filtered water. The 

 water should be such as leaves hardly any residuum when a 

 quart of it is evaporated to dryness; and it must be filtered just 

 before use, to remove any minute organisms, diatoms especially, 

 which it may contain. A certain amount of washing soda will 

 be wanted, if guanos are to be cleaned. 



We will now proceed to consider the manipulations necessary 

 to prepare the various kinds of gatherings, always remembering 

 that these methods will have to be modified to a certain extent 

 for each specimen. 



Recent Gatherings. If there be sand in the gathering, it will 

 be well to remove it before using acid, by shaking it in clean 

 water and pouring off before the diatoms, which are lighter 

 than the sand, settle. The water holding the diatoms in sus- 

 pension may be poured into a test-tube or beaker, the diatoms 

 allowed to settle, and as much of the water poured off as possi- 

 ble. The diatoms are now covered with nitric acid to about the 

 height of half an inch, and allowed to stand for a few minutes. 

 Usually, some chemical action takes place, and it will be well to 

 wait until it subsides. The test-tube or beaker is then held 

 over the lamp and carefully heated until the reaction of the 



