500 SUMMARY OF CURRENT RESEARCHES RELATING TO 



which had passed through the spruce were almost wholly retained by 

 the red cedar. 



It follows that from these three species of wood we can obtain a 

 graded series of strainers, each capable of separating the clay from the 

 diatoms, and at the same time furnishing a ready means of grading as 

 regards size. 



The pine strainer works the most rapidly aud makes a very good 

 separation, and will meet ordinary requirements. The spruce strainer 

 can follow if we want a more thorough gleaning of the smaller forms ; 

 and then we have the red cedar section as a final resort to aid in securing 

 the very smallest diatoms. 



Method for Cleaning Diatomacese.* — There are a number of 

 methods to be found in various books on microscopy for cleaning 

 Diatomacere, none of which, says E. E. Darling, proves to be perfect 

 in all details. The method generally resorted to is to boil with nitric 

 acid. This does not, however, remove all of the organic matter, and 

 leaves a mounted specimen contaminated with black specks. Another 

 method is to boil the specimen with sulphuric acid and potassium 

 chlorate. This, too, has its disadvantage, as in boiling neutral potassium 

 sulphate is formed, this salt being sparingly soluble in water. The 

 following method, which is a modification of that of Edwards,f will be 

 found to work with great success. 



The sample is first dried, and then about 5 grm. taken and well 

 washed with distilled water. The washing is best done by placing the 

 sample in a filtering paper fitted to a glass funnel, and replacing the 

 water as it runs out. The washing is complete when about 250 c.cm. has 

 run through. A hole is then punched in the apex of the filter paper 

 and the sample washed into a 250 c.cm. beaker with concentrated hydro- 

 chloric acid, about 50 c.cm. being required. This is allowed to boil gently 

 for 30 minutes, 100 c.cm. of hot water is then added, and the whole 

 filtered. The sample is washed with hot water until it gives no white 

 coloration when a drop is added to a weak solution of silver nitrate. 

 The sample left on the filter-paper is then washed into the beaker with 

 50 c.cm. of concentrated nitric acid and gently boiled until red fumes 

 cease to be given off. This is then diluted with hot water, filtered, and 

 washed until free from acid. 



The above method removes all the mineral matter except silica, 

 Diatomaceee, and a large part of the organic matter. The product from 

 the last operation is removed to a beaker by means of a small spatula. 

 To this is added a mixture of concentrated sulphuric acid and water, 

 8 parts of acid and 2 parts of water. In mixing care should be taken 

 to add the acid to the water. This is boiled for about 30 minutes, or 

 until the organic matter is charred. As soon as the acid starts to boil 

 weigh out about 2 grm. of potassium chlorate and add to the acid in 

 small quantities until the solution becomes colourless. The acid solution 

 is then poured into 250 c.cm. of distilled water, filtered, and washed free 

 from acid. The product is then washed into a beaker with about 20 c.cm. 



* Amer. Journ. Sci., xxxviii. (1914) p. 282. 

 t See this Journ., 1859, p. 167. 



