APPENDIX 133 



forms will not settle, the others will be perfectly cleaned. When satisfied with the cleaning, 

 preserve the stock material in part alcohol and, in using, pour into a smaller bottle the 

 amount required, replace the dilute alcohol with distilled water, and mount as directed. 

 It often happens that gatherings are made consisting almost entirely of sand. Attempts 

 at cleaning in the usual way will cause the loss of nearly all of the diatoms. In this case, 

 after the material has been treated with acid until nothing remains but sand and a few 

 diatoms, the mechanical finger must be used. 



In the cleaning of marine deposits, various methods may be required. In the case of 

 partly siliceous species, washing in pure water repeatedly is all that can be done. The 

 larger and heavier diatoms may be separated from the sand by elutriation or by whirling 

 in a casserole, by rocking in a shallow dish the shape of a watch crystal, or by pouring 

 slowly over a strip of plate-glass at least two feet in length inclined at an angle of thirty 

 degrees. The sand will cling to the glass, while the greater portion of the diatoms will 

 run off. Where particles of shells or foraminifera are present, a preliminary boiling in 

 hydrochloric acid is advisable. In all marine gatherings, the salt should first be washed 

 out before proceeding with the cleaning. 



For hardened masses of clay and for fossil deposits, it is necessary to boil in carbonate 

 of soda and follow with the acid treatment. Citric acid and acetate of potash used alter- 

 nately in boiling may be tried. Soaking for a time in acetate of potash and allowing the 

 material to deliquesce for a week before further process, has proved successful in some 

 instances. The repetition of several methods and the gentle breaking of the harder masses 

 with the point of a needle will disintegrate almost any diatomaceous earth, but, as a last 

 resort for refractory deposits, boil in pure water, add a piece of caustic potash about the 

 size of a pea, continue the boiling not more than thirty seconds longer, and pour instantly 

 into dilute hydrochloric acid; otherwise the diatoms will be destroyed. Afterwards proceed 

 with the usual treatment. 



Slides and Covers. Take half an ounce of No. 1 covers, circles, and place them in a 

 wide-mouthed bottle. Add a portion of the following mixture (Dr. Carl Seller's formula) : 



Bichromate of potash 2 oz. 



Sulphuric acid 3 fl. oz. 



Water 25 fl. oz. 



Shake the bottle in order that the surfaces of the covers may be fully exposed to the 

 action of the acid, and set aside for several hours. Decant the solution, add water repeat- 

 edly until all traces of the mixture are removed, and keep the circles in the bottle in fifty- 

 per cent, alcohol. When needed, take out a circle with forceps and dry on a linen cloth. 



The slides may be treated in the same way, or they may be easily prepared by immer- 

 sion in a solution of washing soda, and then washed and dried. This process may be used 

 in cleaning the balsam or styrax from old slides. 



Preparation of Strewn Mounts. Place several covers on the mounting stand. With a 

 dipping tube, cover each circle with distilled water, and add a small drop of the prepared 

 diatoms, being careful to avoid any vibration of the stand. Heat the stand until small 

 bubbles begin to appear, remove the lamp, and allow the water to evaporate. If the above 

 method is carefully followed, the diatoms will be deposited in an even layer, provided the 

 material is not too dense. Take a slide, centre it, and place a small amount of styrax on 

 the centre. Invert the prepared cover, and gently place it upon the styrax. Heat the slide 



