112 



THE AMERICAN MONTHLY 



[June, 



Those given by Pritchard ; Dr. A. 

 Mead Edwards in his work on the 

 " Natural History of the Diatoma- 

 cese ;" Dr. Christopher Johnson, of 

 Baltimore, in the Lens, Oct, 1872, 

 and others, are good as far as they 

 go. Cleaning is effectually accom- 

 plished by their processes, but their 

 directions for the separation of the 

 diatoms from the sand and broken 

 diatoms are insufficient. 



The process of prepa^-ing diatoms 

 is simple, but requires great care, 

 time, and patience. When the gather- 

 ing is pure, as in filaments, or on al- 

 gae, the process is easy ; but when 

 the gathering is in the mud of rivers, 

 lakes, and ponds, or in the mud of 

 marshes and harbors, in which there 

 is more or less organic matter, and in 

 lacustrine (sub-peat), sedimentary, 

 sub-plutonic and fossil deposits, it is 

 generally toilsome, tedious, and often 

 difficult. 



The chemicals used are carbonate 

 of soda, liquor potassa, muriatic, nitric 

 and sulphuric acids, bichromate of 

 potash, chlorate of potash, and water 

 of ammonia. The apparatus consists 

 of glass beakers of various sizes, bot- 

 tles, small and large, mostly wide- 

 mouth, evaporating dishes, rubber 

 tubing for syphons of one-eighth inch 

 to one-quarter inch calibre, glass rods, 

 or thick narrow strips of glass for 

 stirring, glass slides, glass dipping 

 tubes, filter-paper, funnels, and a 

 chemist's retort-stand. 



I have found the best commercial 

 acids sufficiently good ; if either 

 need be chemically pure it should be 

 the sulphuric. All the water used in 

 the preparation of diatoms should be 

 distilled or filtered, that there be no 

 admixture of diatoms foreign to any 

 material. For the same reason, the 

 beakers, bottles and dipping tubes 

 should be thoroughly cleansed after 

 use, as diatoms will adhere to them 

 unless great care is taken. I filter 

 water through two thicknesses of 

 druggists' filter paper, a piece of thin 

 muslin being placed between them at 

 the point of the filter to prevent easy 



rupture at that spot. Another desira- 

 ble effect of filtering the water used, 

 is that it is thus rid of much organic 

 and other matter, and is made to 

 practically answer the purposes of 

 distilled water ; besides, the latter is 

 not easily obtained in large quanti- 

 ties, and is expensive. In this article, 

 when water is mentioned, filtered 

 water is to be understood. 



The process of preparing diatoms 

 varies somewhat according as the 

 material may be mud, lacustrine, 

 sedimentary, sub-plutonic, or fossil 

 deposits. I will first describe the 

 treatment of fresh, mud material, and 

 will here say that many of my mani- 

 pulations are derived from directions 

 given by the authors above men- 

 tioned, but some are peculiarly my 

 own. 



Having a quantity of mud material, 

 if in no haste I put it into a wide- 

 mouth bottle, and wash it repeatedly, 

 allowing sufficient time for the ma- 

 terial to settle after each washing, 

 until it finally settles, leaving the water 

 nearly or quite clear. The time re- 

 quired for the material to settle de- 

 pends upon the forms in it, the quan- 

 tity, and the size of the bottle. This is 

 ascertained by examining some of the 

 unsettled portion taken from just 

 above the deposit with a dipping 

 tube. A few drops of this evaporated 

 on a slide and examined under a mi- 

 croscope will tell whether it contains 

 anything more than organic matter. 

 In this way can be ascertained the 

 time required for the material to set- 

 tle before draining off the water. 

 The draining is done with the rubber 

 tube used as a syphon. Having 

 thoroughly washed the material, it is 

 boiled ^for a short time in a solution 

 of carbonate of soda (washing soda), 

 about an ounce to the pint of water, 

 in a glass beaker, then washed as be- 

 fore, till all the alkaline odor and 

 taste have disappeared. This boiling 

 in a solution of carbonate of soda de- 

 stroys considerable of the organic 

 matter, and in a measure cleans the 

 diatoms. I have sometimes used, very 



